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Brush seals are leakage performance systems that are operating against turbine shafts and bucket tips. Flexible bristle structure can compensate the rotor interference during transients, which enables closer clearance control in turbine and turbo-engine applications. During turbomachinery transients, contacting bristles exert force on turbine shaft, which in turn result in wear, frictional heat generation, counter torque and power loss. Brush seal design with proper stiffness has crucial importance since high bristle tip force levels during rotor contact may result in rotor instability, bristle tip melting or thermo-mechanical fatigue due to large amount of local frictional heat input. Counter torque applied by the contacting brush seal with improperly excessive tip force may result in turbine stall and overall efficiency losses. High levels of bristle contact forces may induce elevated wear rates, which degrades the leakage performance of the brush seal during its life cycle. Brush seal contact force evaluation under operating conditions has critical importance and has to be conducted before turbine integration to avoid performance losses and possible turbine failure in some extreme cases. In this paper, ‘Bristle Contact Force Theory’ is developed and closed form bristle tip force (BTF) function is derived where rotor-bristle, inter-bristle and bristle-back plate interactions are included. BTF measurements under pressurized and unpressurized air environment are conducted for the selected test seals by using the custom ‘Rotary Test Rig’. BTF function of bristle contact force theory show high level of correlation with the test data. The effect of cant angle manufacturing tolerance on bristle tip force levels is also examined through bristle tip contact force theory, and compared with the test seal measurements. Methodology for number of bristle row calculation and comparison with the geometric inspection of test seals are also detailed within the content of this paper.

This study investigates the instabilities of the interstage flow between a rotor and a stator in turbomachinery and evaluates their impact on the fan noise. By viewing the interstage flow as the so...

Due to the high Reynolds numbers together with the complex turbulent motions in turbomachinery, selecting a proper turbulence-modeling method is of vital significance in interpreting the real flow ...

For traditional 12/8 bearingless switched reluctance motors (BSRMs), the coupling between torque and levitation increases the complexity of control. For the turbomachinery application, 2 degrees of freedom (DOF) BSRMs stabilized by extra 3-DOF active magnetic bearings are required. In this article, an improved BSRM with 4 rotor poles and 12 stator poles is proposed to realize 4-DOF radial levitation, and the torque dead zone is compensated because that two rotors and these poles are assemble with 15 mechanical degree shifted. The decoupling of torque and radial levitation is realized simultaneously. Moreover, the operation principle of axial reluctance force is analyzed for passive levitation in the axial direction. Various experiments were completed to verify the performance of the proposed BSRM, and the prototype achieved stable levitation of the rotor in 10 000 r/min.

Blade tip-timing is one of the most effective methods for blade vibration parameters identification of turbomachinery. Once-per revolution (OPR) sensor is usually used to determine the rotating speed and as a time reference. However, the OPR sensor leads to a large measurement error or even failure, or it is difficult to install. A new improved two-parameter method without the OPR sensor is proposed to identify the synchronous vibration parameters of variable rotating speed blades. Three eddy current sensors are required to identify the excitation order, vibration amplitude, resonance rotating speed frequency, resonance frequency, and the initial phase of the blades. Numerical simulation of blade synchronous vibration parameters identification is presented, and the identification error of the method is investigated. The simulation results show that the identification accuracy of this method is better than that of the traditional two-parameter method and the improved method in reference, especially in the identification of the vibration initial phase. Experiments are conducted based on the blade tip-timing vibration measurement system. The results indicate that the standard errors of vibration parameter identification results between the new method and the method in reference are smaller, except for the initial phase. It is consistent with the results of the simulation identification. The synchronous vibration parameter identification of variable rotating speed blades without the OPR sensor is achieved based on the new improved two-parameter method.

Shock loss is the primary source of total pressure loss of transonic axial compressors. Reducing the shock by redesigning the geometry of rotor is of great interest for turbomachinery designers. However, the complex flow field involving shock waves, shock-boundary interaction, intense secondary flows, etc., in the compressor makes the design of rotor difficult. The conventional method of design and optimization is computationally intensive and time-costly. This study introduces an inverse design method to design rotor blades corresponding to prescribed isentropic Mach number distributions with no modification of flow-governing equations. An artificial neural network is trained to predict the isentropic Mach number distributions of any deformed blades. Then, with the pattern search optimization, the blade corresponding to the prescribed isentropic Mach number distributions can be achieved. When the aerodynamic parameter database is calculated and the neural network is obtained, this method can design large numbers of blades of changed isentropic Mach number distributions immediately, without modifying the computational fluid dynamics (CFD) flow solver. The design process is fully automatic and efficient. In this study, NASA Rotor 37 is redesigned and optimized as test cases. Some analysis on the influence of blade shape on aerodynamic characteristics of the rotor is represented in this study.

Gas Foil Bearings (GFBs) have fulfilled most of the requirements of novel oil-free turbomachinery. It has been considered as an alternative to traditional bearings in turbopumps, turbocompressors and turbochargers. However, they are prone to instabilities due to its low damping characteristics. Therefore, a hybrid bearing combining the GFBs and Active Magnetic Bearings (AMBs) has been in rigorous study due to its obvious advantages. The main aim of this paper is to provide a coupled time domain numerical model of the rotor supported on hybrid GFBs. The developed non-dimensional model has been used to investigate the capability of hybrid GFBs to mitigate the effect of unbalance force and in turn instability. Further, the ability of the hybrid GFB to withstand unbalance at an arbitrary time has also been investigated. The magnetic force generated is calculated using reluctance network method while fluid film forces are obtained by solving the governing Reynolds equation. The magnetic force of the AMB is non-dimensionalized in line with the fluid film forces of the conventional GFB. The non-dimensionalized fluid film forces from the GFBs and the electromagnetic forces from the EMAs are integrated into the equations of motion of the rotor. The response is then recorded for different operating parameters of the rotor. The sub-synchronous frequency which is the dominating frequency in case of the conventional GFB is eliminated due to the implementation of hybrid GFB. It has been demonstrated that the hybrid GFB has higher capability to withstand unbalance compared to conventional GFB. It has been observed that higher control current is required for higher unbalance eccentricity. Moreover, the hybrid GFB is also capable of adapting to the unbalance occurring at an arbitrary time.

Surface roughness is a critical health parameter of a turbine blade due to its implications on blade surface heat transfer and structural integrity. This paper proposes a physics-based online framework for Gas Turbine Engines (GTE), in order to assess the blade surface roughness in a high-pressure turbine without engine shutdown. The framework consolidates Gas Path Analysis (GPA) based performance monitoring models and meanline turbomachinery analysis, using a novel GPA-meanline matching process. This extracts meaningful performance deviation trends from GPA, while addressing the uncertainties associated with the measurements and modelling. To relate efficiency loss to surface roughness severity, a meanline-based system-identification process has been developed to establish the meanline representation of the turbine stage, and to incorporate the empirical surface roughness loss correlations. The roughness loss correlations have been evaluated against recent transonic test data in the literature. A modification to the compressibility correction factor has been made according to the evaluation outcome, which improved loss predictions compared to the experimental measurements. The framework was tested on the three-year operational data of a cogeneration GTE, and the results verified the framework's potential for online surface roughness monitoring. The predicted surface roughness showed agreement in both trend and the magnitude-level with the measurements reported in the literature.

Porous gas bearings (PGBs) have a proactive application in aerospace and turbomachinery. This study investigates the gas lubrication performance of a PGB with the condition of velocity slip boundary (VSB) owing to the high Knudsen number in the gas film. The Darcy-Forchheimer laws and modified Navier-Stokes equations were adopted to describe the gas flow in the porous layer and gas film region, respectively. An improved bearing experimental platform was established to verify the accuracy of the derived theory and the reliability of the numerical analysis. The effects of various parameters on the pressure distribution, flow cycle, load capacity, mass flow rate, and velocity profile are demonstrated and discussed. The results show that the gas can flow in both directions, from the porous layer to the gas film region, or in reverse. The load capacity of the PGB increases with an increase in speed and inlet pressure and decreases with an increase in permeability. The mass flow rate increases as the inlet pressure and permeability increase. Furthermore, the simulation results using VSB are in agreement with the experimental results, with an average error of 3.4%, which indicates that the model using VSB achieves a high accuracy. The simulation results ignoring the VSB overrate the load capacity by 16.42% and undervalue the mass flow rate by 11.29%. This study may aid in understanding the gas lubrication mechanism in PGBs and the development of novel gas lubricants.

By means of experimental measurement of the transient internal flow field and the periodic lumped-blade separation analysis method (PLSAM), the pressure field distribution on a stator blade surface and the corresponding flow-induced pulsation, as well as the fluctuation characteristics in a torque converter are acquired and further analysed. The results show that there are fluctuation characteristics in both the blade pressure distribution results and the blade torque under the influence of flow induced pulsation, while the relationship between these fluctuations and the rotatory angle of the wheels reveals the mechanism of the flow induced pulsation; namely, the main cause of the flow induced pulsation lies in the successive switching of the turbine/pump blade position relative to the stator, which can be modelled by a trigonometric function in both the space domain and time domain, while the frequency domain characteristics of this trigonometric function exist in both the internal flow characteristics and performance results, which allows a connection to be built between the macro-performance and the micro-internal flow character and can be used for the inverse design of the cascade system.

Fossil fuels are energy sources that supply a large part of the world's energy generation. However, they produce greenhouse gases such as carbon dioxide (CO2), nitrogen oxide (NOx) and particulates that increase global warming. For this reason, other forms of renewable energy such as hydropower have begun to be implemented through turbomachinery such as Pelton turbines, which significantly reduce these emissions since they are highly efficient turbines based on the use of natural resources (water). Pelton turbines are based mainly on three components for their operation, which are the Pelton injector, the bucket and the wheel. The injector is an important component in the energy transformation of Pelton turbines. Although to analyze its behavior, it is possible to use fluid dynamics (CFD) software to predict the trajectory of the flow through a solid or free surface. The objective of this work is to analyze by means of computational fluid dynamics (CFD) the incidence of the length and the needle tip angle of a Pelton turbine injector on the generated power. For this, an ANSYS 2020R2 computational fluid analysis software was used to study how the variation of the injector needle tip angle influences through the volume of fluid (VOF) method, starting from the generation of a commercial model with a tip angle of 60° and two (2) geometries of 55° and 75° respectively. Numerical results show a better performance for the 75° angle of 96 % and lower for the 55° and 60° with 94.1 % and 95.5 % respectively, whereby steeper angles achieve higher performances. In summary, the present study pretends to increase the power generation, in the face of phenomena occurred in the energy transfer. Although the performance of the injector in each angle configuration must be tested in practice

Mixed flow turbines are widely used in several industrial applications covering turbomachinery, automotive engineering and electricity production. For decades, it is well known that mixed flow turbines are a seat of several loss phenomena such as the volute to rotor interspace loss, subject of this paper. Commonly, the meanline approach is the first step solution for building a preliminary design of such turbines and estimating subsequent losses. The accuracy of the code used in the meanline modeling is crucial for building an optimized turbine design with a minimized loss generation. This paper presents an improved validated meanline code, written in the newest object-oriented version of the FORTRAN language, for turbomachinery performance prediction. Unlike commercially available codes, the code allows the calculation of the rotor passage loss coefficient given the turbine expansion ratio without the need for additional test data. The standard deviation value between the code and test data is less than 10%, for all studied cases which ensure the validity of the developed model. Then, the developed code is exploited to investigate the effect of the volute to rotor interspace geometry on the loss generation and performance of a mixed flow turbine. Indeed, a performance distribution over a wide range of rotational speed and an energy loss breakdown are depicted and discussed showing a significant impact of the volute to rotor interspace. The results revealed an improvement in the turbine efficiency up to 2.9% with a volute to rotor interspace radii ratio of 0.59 at 80% of the design speed.

Gas foil bearings are often used in high-speed turbomachinery such as turboexpanders and turbochargers due to their merits over simple gas-lubricated bearings. The merits of gas foil bearings include their ability to tailor dynamic parameters such as stiffness and damping. Gas foil bearings usually have low clearance and operate at a high rotational speed, which eventually leads to velocity slip at the solid–fluid interface. This article investigates the effect of slip flow on various parameters of gas foil thrust bearings. A numerical model is formulated to predict pressure, film thickness and temperature distribution of helium lubricated gas foil thrust bearing at high rotating speed. The Reynolds equation is modified by assuming first-order slip coupled with the structural (compliant) and energy equation. The temperature-dependent viscosity and density of the fluid are also considered in the Reynolds equation to predict the thermohydrodynamic behaviour of gas foil thrust bearings. The numerical model thus developed uses a finite-difference method and the Newton–Raphson method to solve the Reynolds equation,whereas the successive over-relaxation method is used to solve the energy equation. Various performance parameters are compared for slip and no-slip conditions for gas foil thrust bearings. The results show a considerable difference between the two phenomena. Also, the conventional Reynolds equation tends to overestimate the load-carrying capacity.

This work proposes a novel hybrid gas-magnetic bearing (HGMB) which has single bearing structure. The gas bearing and the active magnetic bearing (AMB) share the same airgap, and the closed magnetic poles are taken as the bushing of the gas bearing. Controllable electromagnetic forces are applied to adjust system dynamic characteristics. Numerical results demonstrate better rotating accuracy, suppressed sub-synchronous vibration, lower energy consumption compared with rigid gas bearings and AMB, and less air friction losses than conventional HGMBs, indicating the suitability of the proposed bearing for cryogenic turbomachinery.

Nub-and-sleeve of last-stage blade for steam turbine is a part-span damper. The nub is susceptible to fretting cracking since the nub is in contact with the sleeve under centrifugal force and vibration of blade causes a small-amplitude oscillatory movement at the nub-sleeve contact interface. Previous study of the authors achieved the experimental result that the minimum tangential contact force amplitude for cracking increases almost proportionally to the normal contact force when the nub-sleeve contact interface is in partial slip state. Present study aims at establishing the fretting cracking condition for nub that can be applicable to design of nub-and-sleeve. For this purpose, the experimental result was analyzed with fatigue damage parameters: Smith-Watson-Topper, Fatemi-Socie and Crossland. Finite element analyses were carried out to obtain stress and strain data for estimation of fatigue damage. It is demonstrated that the fretting cracking of nub can be predicted with a single fatigue damage parameter value in a range of the normal contact force if plasticity is considered. However, if plasticity is ignored, the minimum fatigue damage parameter value for cracking increases with the normal contact force.

The present paper discusses the study of longitudinal vibrations in turbomachines coupled with skewed slotted bar cage induction motors and which are of the typical configurations in refinery industries. Based on vibration data, the severe longitudinal vibrations in tilting pad thrust bearing assembly and its failure mechanism during start up transient and steady-state operations has been observed. The excitation sources for these longitudinal vibrations originates from asymmetric air gaps in cage induction motors. Hereby, the study of longitudinal vibrations in turbomachines with thrust bearing is found to be necessary. A simplified Single degree freedom (SDOF) analytical model is proposed to estimate the peak response based on tuned variable stiffness method. Uniform air gap with rotor skew causes fixed thrust and is proportion to square of the load current. Static eccentricity across the rotor motor air gap causes variations in gap length and intern creates the torque fluctuations. This value is proportional to variance in square of the load current. In the proposed model evaluates the cascade effect of preloaded thrust due to rotor motor skewness and followed by compressor thrust due to differential pressure across the impeller in the form of the variable stiffness. This model has advantage in analysing the coupled motor and turbomachinery system response in longitudinal direction in a simple manner. The longitudinal vibrations estimate at thrust bearing and compared with experimental vibration data obtained from the field machinery. There is a good convergence between results of the analytical model and experimental field vibration data.

Підвищення потужності енергоблоків атомних станцій є світовою тенденцію та широко реалізується в країнах Європи та Сполучених шатах Америки. Зазвичай роботи з підвищення потужності блоків атомних станцій проводяться під час планових реконструкцій. Особливостями такої реконструкції є часткова заміна обладнання, що у порівнянні з повною дає значну економію ресурсів. Використання такого підходу дозволяє частково замінити елементи проточної частини, що в свою чергу виконується з метою для забезпечення необхідних параметрів течії в проточній частині турбомашини, а також дозволяє повторно використовувати не модифіковані елементи конструкції. Ця стаття містить узагальнення досвіду АТ «Турбоатом» з проведення вдосконалення циліндру високого тиску, а також розглядаються конструктивні особливості проекту модернізації турбоустановки К-1000-60/1500-2 блоку 4 Балаковської АЕС виробництва ПАТ «Турбоатом». В рамках проекту модернізації АТ «Турбоатом» виконав комплекс теплових і міцністних розрахунків ЦВТ турбіни К-1000-60/1500-2 з урахуванням підвищення теплової потужності реактора до 3210 МВт з використанням існуючих деталей і вузлів. Прийняті конструкторські і схемні рішення в проекті модернізації турбоустановці К-1000-60/1500-2 бл. 4 Балаковської АЕС і високий ступінь уніфікації її елементів, відпрацьованих і освоєних у виготовленні і експлуатації на станціях, сприяють підвищенню якості її технічного обслуговування і ремонтів, дозволяють вважати, що ця турбоустановки матиме високі техніко-економічні показники, а також забезпечують її високу конкурентоспроможність на зовнішньому ринку. Удосконалена проточна частина ЦВТ оснащена розвиненою системою видалення вологи. Відведення вологи з міжвінцевих зазорів здійснюється системою дренажних отворів в надбандажних козирках діафрагм. Волога з межступеневих зазорів відводиться в камери видалення вологи за робочими лопатками. Ефективність видалення вологи за робочими лопатками забезпечується конічним меридіональним обводом робочих лопаток і вологосборними канавками на бандажах робочих лопаток. Розрахункова величина збільшення електричної потужності турбоустановки К-1000-60/1500-2 бл. 4 Балаковської АЕС при підвищенні теплової потужності реактора до 3210 МВт становить 52,56 МВт., ncreasing the capacity of nuclear power plants is a global trend and is widely implemented in Europe and the United States. Usually, work to increase the capacity of nuclear power units is carried out during planned reconstructions. Features of such reconstruction are partial replacement of the equipment that in comparison with full gives considerable economy of resources. The use of this approach allows partially replacing the elements of the flow part, which in turn is performed in order to provide the necessary flow parameters in the flow part of the turbomachine, and also allows reusing unmodified structural elements. This article summarizes the experience of JSC "Turboatom" in improving the high pressure cylinder, as well as the design features of the project to modernize the turbine K-1000-60 / 1500-2 unit 4 Balakovo NPP produced by JSC "Turboatom". As part of the modernization project, JSC "Turboatom" performed a set of thermal and strength calculations of the HPC of the turbine K-1000-60 / 1500-2, taking into account the increase in thermal capacity of the reactor to 3210 MW using existing parts and assemblies. The design and circuit decisions in the project of modernization of the turbine K-1000-60 / 1500-2 4-th block Balakovo NPP and a high degree of unification of its elements, worked out and mastered in the manufacture and operation of stations, improve the quality of its maintenance and repairs, allow us to believe that this turbine will have high technical and economic performance, as well as ensure its high competitiveness on the outside market. The advanced flowing part of HPC is equipped with the developed system of removal of moisture. Moisture removal from the intercrown gaps is carried out by a system of drainage holes in the diaphragm visors. Moisture from the interstage gaps is discharged into the moisture removal chamber behind the blades. The efficiency of moisture removal behind the blades is provided by a conical meridional circumference of the blades and moisture-collecting grooves on the bandages of the blades. The estimated value of the increase in electric power of the turbine K-1000-60 / 1500-2 4-th block Balakovo NPP with increasing the thermal capacity of the reactor to 3210 MW is 52.56 MW., Повышение мощности энергоблоков атомных станций является мировой тенденции и широко реализуется в странах Европы и Соединенных одеждах Америки. Обычно работы по повышению мощности блоков атомных станций проводятся во время плановых реконструкций. Особенностями такой реконструкции является частичная замена оборудования, что, по сравнению с полной, дает значительную экономию ресурсов. Использование такого подхода позволяет частично заменить элементы проточной части, что в свою очередь выполняется с целью для обеспечения необходимых параметров течения в проточной части турбомашины, а также позволяет повторно использовать модифицированные элементы конструкции. Эта статья содержит обобщение опыта АО «Турбоатом» по проведению совершенствования цилиндра высокого давления, а также рассматриваются конструктивные особенности проекта модернизации турбоустановки К-1000-60 / 1500-2 блока 4 Балаковской АЭС производства ОАО «Турбоатом». В рамках проекта модернизации АО «Турбоатом» выполнил комплекс тепловых и прочностных расчетов ЦВД турбины К-1000-60/1500-2 с учетом повышения тепловой мощности реактора до 3210 МВт с использованием существующих деталей и узлов. Принятые конструкторские и схемные решения в проекте модернизации турбоустановке К-1000-60 / 1500-2 бл. 4 Балаковской АЭС и высокая степень унификации ее элементов, отработанных и освоенных в производстве и эксплуатации на станциях, способствуют повышению качества ее технического обслуживания и ремонтов, позволяют считать, что эта турбоустановка обладает высокими технико-экономические показателями, а также обеспечивает ее высокую конкурентоспособность на внешнем рынке. Усовершенствованная проточная часть ЦВД оснащена развитой системой удаления влаги. Отвод воды из межвенцовых зазоров осуществляется системой дренажных отверстий в надбандажних козырьках диафрагм. Влага из межступеньчатых зазоров отводится в камеры удаления влаги с рабочими лопатками. Эффективность удаления влаги с рабочими лопатками обеспечивается конической меридиональным окружностью рабочих лопаток и влагосборными канавками на бандажах рабочих лопаток. Расчетная величина увеличения электрической мощности турбоустановки К-1000-60 / 1500-2 бл 4 Балаковской АЭС при повышении тепловой мощности реактора до 3210 МВт составляет 52,56 МВт.

This paper is focusing on diagnosis for longitudinal and radial vibrations of turbomachinery coupled with induction motors. In this context, extensive field vibration measurements are conducted and analysed to identify the source of predominant vibrations on rotor bearing system in a chosen centrifugal compressor in the radial and longitudinal directions. As a first step, the measured overall vibration levels at multiple locations on bearing surface are compared with the existing ISO standard limits. These measurements showed severe longitudinal vibration values and failure of thrust collar assembly which were not considered in turbomachinery (API) design standards. The second step in diagnosis for vibration spectrum measurements are conducted both in longitudinal and radial directions during transient and steady state operations to find the vibration source and thrust collar assembly failure mechanism. This study on vibration diagnosis and analysis on turbomachinery is useful in correcting the severe longitudinal vibrations and damage control measures and corrections associated with static eccentric airgaps through motor air gap diagram.

A simple-to-implement technique for measuring radial clearances with controlled precision due to decreasing random components of errors is considered. The quantitative estimates of precision, performance, and efficiency of the proposed technique are provided. This technique is stochastic, is based on characteristics of random errors and on periodicity of blade wheel rotation, and allows obtaining the measurement results with uniform precision in the entire range of rotation speeds of the turbomachine rotor. The considered technique makes it possible to avoid procedures for approximating numerical readouts.

A novel method for estimating the rotor blade life cycle of an industrial gas turbine (GT) by the use of artificial Neural Network is proposed in this paper At the first step the blade life cycle is obtained by the use of Larson–Miller method which uses output results of GT performance modeling and blade thermal-mechanical data. Then results of rotor blade life cycle analysis by the above method are compared with results of stress factor curve (which is provided by manufacturers). Comparison of results revealed an average difference value of 9.7 % between blade life cycle estimation by two above mentioned methods. In the next step, by input data such as mass flow rate, temperature and pressure of hot flue gas, the output data such as blade cooling air and turbine shaft rotational speed are obtained from GT modeling. Then blade life cycle are also obtained by Larson–Miller​ method for 811 sample points of GT operating conditions for various ambient temperatures and load ratios. These data are used for neural network training. Results show that life cycle estimated values by neural network method in comparison with life cycle estimated values by Larson–Miller method, had about 4.8% error value in maximum (with 10-4 as mean square error, MSE). Finally, by the use of neural network method, the effects of gas turbine operating and health conditions (at various ambient temperatures, GT load ratios and compressor fouling levels) on blade life cycle are investigated. If we expect to get the nominal power output of clean blade at ISO ambient condition, in ambient temperature range of 15 to 45 oC, the GG turbine first rotor blade life cycle reduces from 4.85 to 0.07 and in the range of 0 to 7% compressor fouling, turbine blade life cycle reduces from 4.85 to 0.68 years.

The helical grooved seal, which is a non-contact sealing device using the viscosity of the fluid, prevents leakage by reducing fluid pressure according to the shapes of the rotor and stator. It has been widely adopted to turbomachinery because no wear deliveries high efficiency, unlike to the existing contact sealing device. In this study, parametric study was performed by CFD analysis, considering helical grooved seal shape: ratio of groove width and land width (Wratio), helical angle (β) and groove depth (d). Based on the leakage characteristics analyzed through CFD results, improved seal shape of the helical grooved seal to reduce leakage was suggested.

The nuclear reactor coupled with supercritical carbon dioxide (S-CO2) Brayton cycle has good prospects in generation IV reactors. Turbomachineries (turbine and compressor) are important work equipment in circulatory system, whose performances are critical to the efficiency of the energy conversion system. However, the sharp variations of S-CO2 thermophysical properties make turbomachinery performances more complex than that of traditional working fluids. Meanwhile, almost no systematic analysis has considered the effects of turbomachinery efficiency under different conditions. In this paper, an in-house code was developed to realize the geometric design and performance prediction of S-CO2 turbomachinery, and was coupled with systematic code for Brayton cycle characteristics analysis. The models and methodology adopted in calculation code were validated by experimental data. The effects of recompressed fraction, pressure and temperature on S-CO2 recompression Brayton cycle were studied based on detailed design of turbomachinery. The results demonstrate that the recompressed fraction affects the turbomachinery characteristic by changing the mass flow and effects the system performance eventually. By contrast, the turbomachinery efficiency is insensitive to variation in pressure and temperature due to almost constant mass flow. In addition, the S-CO2 thermophysical properties and the position of minimum temperature difference are significant influential factors of cyclic performance.

Nub-and-sleeve of last-stage blade for steam turbine is a part-span damper. The nub is vulnerable to fretting cracking since it is in contact with the sleeve under centrifugal force, and a small-amplitude oscillatory movement occurs at the nub-sleeve contact interface due to the blade vibration during operation of turbine. The present study developed a rig test that mimics fretting behavior at the nub-sleeve contact interface and reproduces fretting cracking of the nub. The rig tests reveal that fretting cracking occurs if the contact interface is in partial slip state and the tangential contact force amplitude is sufficiently large. The minimum tangential contact force amplitude for cracking increases with the normal contact force. Moreover, under the partial slip condition, the tangential contact force amplitude increases with the imposed displacement amplitude and its maximum value increases with the normal contact force.

With increasing need for energy efficient vapor-compression cycles (VCCs), researchers have investigated different aspects of such systems to increase performance. The goal of this research is to experimentally investigate the design and control of a turbomachine expander to recover work and control the VCC. An R-410A split-system heat pump experimental setup has been utilized to compare the performance and control capabilities of a variable nozzle and a fixed nozzle with phase separation combined with evaporator bypass flow metering. A theoretical analysis on the benefit of the expander in heat pumps motivated heat pump operation in cooling mode. The variable nozzle experiments yielded a significant decrease in expander isentropic efficiency, and the evaporator bypass control led to an increase in system coefficient of performance (COP) of 2.3% with an expander overall isentropic efficiency of 18.8%. Compressor suction superheat control was achieved with the evaporator bypass over a range of ambient conditions.

Advances in the development of analysis and design methods for fluid-flow machines have enabled both their multi-criteria optimisation and miniaturisation. To decrease the size of such a machine whilst, at the same time, maintaining its output power level, the rotor’s rotational speed needs to be increased. It is the reason for serious difficulties with respect to the rotor dynamics and the selection of a bearing system. This article discusses the simulation analysis and experimental research carried out on a prototypical microturbine, designed for use in a domestic ORC (organic Rankine cycle) cogeneration system. During the design process, the basic assumption was to develop a turbomachine, whose dimensions would have been as small as possible and whose output electric power would have been about 1 kilowatt. A supersonic impulse turbine, with a nominal rotational speed of 100,000 rpm, was used in order to obtain high flow efficiency. The maximum speed of the rotor was determined at a level of 120,000 rpm. The article presents the results of analyses made at the design stage and preliminary results of the experimental research. The numerical simulations covered the bearing system optimisation and the rotor dynamics analysis. Next, based on the outcomes of these analyses, a decision was made to use non-conventional gas bearings which are fed by the low-boiling medium’s vapour that comes from the ORC system. Within the framework of the experimental research, the dynamic behaviour of the turbogenerator was examined in terms of the rotational speed and produced energy. The performed measurements are proof of very good dynamic properties of the tested machine and after the research was over it was concluded that there were absolutely no signs of wear of the turbogenerator’s subassemblies.

Purpose The purpose of the paper is to quantify the impact of the non-uniform flow generated by the upstream stator on the generation and convection of the tip leakage flow (TLF) structures in the passages of the rotor blades in a low-speed axial fan. Design/methodology/approach A full three dimensional (3D)-viscous unsteady Reynolds-averaged Navier-stokes (RANS) (URANS) simulation of the flow within a periodic domain of the axial stage has been performed at three different flow rate coefficients (φ = 0.38, 0.32, 0.27) using ReNormalization Group k-ε turbulence modelling. A typical tip clearance of 2.3 per cent of the blade span has been modelled on a reduced domain comprising a three-vaned stator and a two-bladed rotor with circumferential periodicity. A non-conformal grid with hybrid meshing, locally refined O-meshes on both blades and vanes walls with (100 × 25 × 80) elements, a 15-node meshed tip gap and circumferential interfaces for sliding mesh computations were also implemented. The unsteady motion of the rotor has been covered with 60 time steps per blade event. The simulations were validated with experimental measurements of the static pressure in the shroud of the blade tip region. Findings It has been observed that both TLF and intensities of the tip leakage vortex (TLV) are significantly influenced by upstream stator wakes, especially at nominal and partial load conditions. In particular, the leakage flow, which represents 12.4 per cent and 11.3 per cent of the working flow rate, respectively, has shown a clear periodic fluctuation clocked with the vane passing period in the relative domain. The periodic fluctuation of the TLF is in the range of 2.8-3.4 per cent of the mean value. In addition, the trajectory of the tip vortex is also notably perturbed, with root-mean squared fluctuations reaching up to 18 per cent and 6 per cent in the regions of maximum interaction at 50 per cent and 25 per cent of the blade chord for nominal and partial load conditions, respectively. On the contrary, the massive flow separation observed in the tip region of the blades for near-stall conditions prevents the formation of TLV structures and neglects any further interaction with the upstream vanes. Research limitations/implications Despite the increasing use of large eddy simulation modelling in turbomachinery environments, which requires extremely high computational costs, URANS modelling is still revealed as a useful technique to describe highly complex viscous mechanisms in 3D swirl flows, such as unsteady tip flow structures, with reasonable accuracy. Originality/value The paper presents a validated numerical model that simulates the unsteady response of the TLF to upstream perturbations in an axial fan stage. It also provides levels of instabilities in the TLV derived from the deterministic non-uniformities associated to the vane wakes.

Purpose The paper aims to present an outline of the technology of the active anti-surge algorithm based on high-frequency pressure measurement. The presented system is fast, inexpensive and reliable and does not limit the machine-operating range. Many contemporary anti-surge systems are based on theoretical surge margin. This solution limits machine operating range by about 10-15 per cent in the region of the highest pressure ratios. It is also often sensitive to change in external conditions such as temperature or density, as the system reacts to limits calculated theoretically. Design/methodology/approach This paper presents results of pressure measurements obtained on the low-speed centrifugal blower DP1.12. The pressure signals were presented in the form of phase diagrams, and conclusions were drawn from their phase portraits to develop the surge indication parameter. Findings The presented safety system uses the signal to develop the so-called (rate of derivative fluctuation) RDF parameter. In nominal working conditions, this parameter keeps the value close to 1. When RDF reaches values over 3, the anti-surge procedure should be implemented. Experimental studies have shown that this algorithm assures enough time to incur actions suppressing unstable phenomena. Originality/value The system reacts to real machine working conditions and is hence reliable. The RDF algorithm could also be used to identify local flow instabilities, as well as off-design operation.

Rotor active magnetic bearings system is the most efficient supporting technique of high-speed rotating machinery. This work aims to explore the dynamical behaviors of the 6-pole rotor active magnetic bearings system for the first time. Two different control strategies are introduced to mitigate the considered system lateral vibrations and the corresponding whirling motions. The first control technique (Radial control) is suggested such that the attractive magnetic force in each pole is proportional to both the radial displacement and radial velocity of the rotating disk toward that pole. The second control strategy (Cartesian control) is proposed such that the controlled magnetic force in each pole is designed to be proportional to both the cartesian displacement and cartesian velocity of the rotating disk in two perpendicular directions. Based on the proposed control strategies, two nonlinear dynamical models are derived and then analyzed by applying perturbation methods. Different response-curves and bifurcation diagrams are plotted utilizing the disk spinning-speed and the disk eccentricity as bifurcation control parameters. The main obtained analytical and numerical results illustrated that the considered system can perform a circular forward whirling motion only under the first control technique, while four whirling modes (that are forward whirling, backward whirling, both forward and backward whirling, and oscillation along a straight line) are noticed in the second control method depending on the disk spinning speed. Moreover, it is found that the radial control method is robust against the system instability than the cartesian control one, especially at large disk eccentricity. However, the cartesian control method could exhibit a vibration suppression efficiency higher than the radial control one at small disk eccentricity.

Computer Numerical Control (CNC) milling is still today the elective process for the production of single-piece impellers, as it can reliably produce complex geometries, removing the need for additional manufacturing processes. Nevertheless, Additive Manufacturing is winning more and more ground due to its ability to make components of any geometry that cannot be produced using subtractive techniques. As a result, the use of this technology can eventually be seen as the key to develop high-performance rotor components. In this scenario, the design of 3D impellers does not make an exception. Accordingly, the present paper proposes a general framework for engineered re-design and manufacture of 3D impellers installed on centrifugal compressors by exploiting Topology Optimization and Additive Manufacturing's potential. The procedure investigates also the rotoric component's best configuration for both static and dynamic behavior. Finally, the topology-optimized component is produced with AM through the use of suitable materials that can ensure efficient mechanical efficiency to prove the manufacturability of the entire procedure. To validate the proposed framework, the complete re-design of a 3D impeller of a major Italian-based Oil & Gas company is carried out, demonstrating that the re-thinking of the component in terms of Topology Optimization is a straightforward approach to increase the overall performance of the produced rotoric part.

The manufacturing of turbomachinery components for the aerospace sector is an important topic in machining research. Aeroengine manufacturing companies forecast increasing levels of design complexity and demand in the following years. Key elements are the Integral Bladed Rotor (IBR) parts, such as impellers and blade-disks. Despite advances in five-axis machining, manufacturing a reliable and efficient IBR component is still a challenge. In this work, the mechanics of the milling process with barrel-shape cutter is studied. These recently developed tools offer a potential advantage for a productive, chatter-free, high-performance machining of IBR parts. In this work, the cutting forces model is developed for this type of tools, then the model is verified in inclined milling operations.

A numerical investigation is conducted for the flow between two concentric cylinders with a wide gap, relevant to bearing chamber applications. This wide gap configuration has received comparatively less attention than narrow gap journal bearing type geometries. The flow in the gap between an inner rotating cylinder and an outer stationary cylinder has been modelled as an incompressible flow using an implicit finite volume RANS scheme with the realisablek-εmodel. The model flow is above the critical Taylor number at which axisymmetric counterrotating Taylor vortices are formed. The tangential velocity profiles at all axial locations are different from typical journal bearing applications, where the velocity profiles are quasilinear. The predicted results led to two significant findings of impact in rotating machinery operations. Firstly, the axial variation of the tangential velocity gradient induces an axially varying shear stress, resulting in local bands of enhanced work input to the working fluid. This is likely to cause unwanted heat transfer on the surface in high torque turbomachinery applications. Secondly, the radial inflow at the axial end-wall boundaries is likely to promote the transport of debris to the junction between the end-collar and the rotating cylinder, causing the build-up of fouling in the seal.

Supercritical carbon dioxide power cycle (sCO2) has recently attracted a great deal of interest owing to its compact size and potential for achieving high efficiency over a wide temperature range. However, several challenges still need to be overcome before the sCO2 cycle can be commercialized. One such challenge is leakage at the rotor components. The present paper discusses an innovative heat-pump application that can be used for leakage reinjection. The unique consideration of this leakage supplement system for the supercritical CO2 cycle stems from the high energy density of sCO2 and the high rotational speeds seen in turbomachinery. This paper proposes a heat-pump system that collects CO2 leakage at the turbine and liquefies this gas at the evaporator. The liquefied CO2 is then pressurized to the high pressure required for the main power generating cycle, and subsequently heat from the heat-pump working fluid is transferred to the CO2 in the heat-pump condenser. This heat-pump system offers superior compression performance over conventional methods of reinjection. Thermodynamic analysis reveals that the performance of the heat-pump system is sensitive to the saturation temperature of CO2 in the evaporator and superheating at the heat-pump's compressor inlet. Then, the genetic algorithm optimization module in MATLAB is used to optimize the system for net power consumption. Various heat-pump working fluids are investigated; R290 (Propane) delivers the best performance at 38.9% reduction in net power compared to a base case.

Constant volume combustion (CVC) is a promising way to substantially increase gas turbine efficiency. Shockless explosion combustion and pulsed detonation combustion are potential candidates for CVC integration in gas turbines. Both these schemes operate with sequentially ignited tubes that introduce highly transient flow characteristics in neighboring machine components. One of the most critical parts of turbomachinery is the compressor. In this work, the impact of the firing pattern on the flow field in a compressor stator located upstream is studied. In particular, five combustion patterns are investigated in terms of local blockage and compressor performance. As wake measurements indicate, patterns with low fluctuations of local blockage exhibit less flow deflection, reduced losses, and higher pressure increases compared to those with large fluctuations. Furthermore, the effect of active flow control (AFC) utilizing end-wall blowing is investigated. Experiments show that the impact of AFC varies depending on the pattern, favoring patterns with low fluctuations of local blockage. The results indicate that closed-loop AFC is favorable when a disturbance rejection is of interest but does not significantly improve performance compared to steady blowing.

Turbomachinery has a vital role in industrial engineering and is used for transfer of energy. Bladed disks such as compressor, impeller pumps, turbine generator and jet engines are the critical components of turbomachinery. In this research we have focused on bladed disks of the turbine. It deals mistuning effect on the disks that creates lack of symmetry in the turbine blade. Due to lack of symmetry in extreme operation, turbine blades may cause an increased force response due to fatigue and may result in unexpected failure. This effect on the turbine disk may happen due to certain material properties and manufacturing restraints. In order to understand the actual meaning of mistuning effect on the turbine disk, the study of model parameters of turbo machinery blade is very important. These parameters are very sensitive to these mistuning patterns that are inherent in the structure. Moreover, cracks formation besides mistuning is another factor that effects the turbine disk. This causes stiffness loss at crack location; stiffness loss alters the dynamics of the structure. This paper gives an insight to determine the effects of presence of crack and mistuning levels in mistuned turbine blade by using smeared material properties and modal assurance criterion (MAC) techniques. Mistuning at mistuned zone causes a split in vibration modes that are represented by gradual increase of ‘E’ (Modulus of Elasticity) value of certain elements in finite element analysis (FEA). A comprehensive way of finding complex mistuned patterns in repeating structures has been practiced in this work. Furthermore, the characteristics of mistuned blisk model having cracks of various patterns regarding its depth and location are compared with the tuned blisk model to determine the severity of damage occurred. For investigation purposes, the crack model mode shapes are obtained by penetrating the cracks at four different locations one after the other successively. The change in mode shapes and MAC results indicates the severity of damage with the crack depth ratio at certain location. A numerical value of damage is obtained by subtracting MAC matrices of crack damaged model from MAC metrics of reference model.

The aerodynamic and aeroelastic study of flow through turbomachine blade passage is the most essential requirement for the development of fuel-efficient gas turbine engines. The use of various cascade tunnels is very common to predict the flow behaviour within the blade passage and at the exit of cascade blades. The present work focuses on the innovative method for the development of annular sector cascade wind tunnel of exit Mach number 0.62 for such applications, using the computational study. The flow behaviour within the tunnel was numerically analysed using commercial software, ANSYS CFX®. To meet the special requirements/constraints like available laboratory space and height of the test section, the numerical study was explored for various design iterations. The use of a wide-angle diffuser with inclination was one of the challenges which were addressed using a porous screen. The modelling for the screens and honeycomb section are the most challenging aspects, which were resolved using porous media option with porosity and permeability as an input. The numerical method discusses to define the outlet flow domain as a half-spherical shape with opening boundary condition to simulate the actual exhaust flow condition. The cost-effective honeycomb section, with square-shaped cells, which are easy to manufacture and clean, worked effectively to straighten the flow by reducing velocity fluctuations in the lateral and longitudinal direction. The settling chamber screens reduced the streamwise velocity fluctuations, and accelerating flow in the contraction duct reduced the spatial variation. Near about less than 7% RMS change in the contraction duct exit velocity was achieved as it is the need to test the turbine blades. It is strongly believed that the various design aspects will help future designers for selecting various geometrical parameters for the design and development of such cascade tunnels.

Computational fluid dynamics (CFD) is the most current technology in the fluid flow study. Experimental methods for predicting the turbomachinery performance involve greater time consumption and financial resources compared to the CFD approach. The purpose of this article is to present the analysis of CFD simulation results in a centrifugal fan. The impeller was calculated using the one-dimensional theory and the volute the principle of constant angular momentum. The ANSYS-CFX software was used for the simulation. The turbulence model adopted was the SST. The simulation provided the characteristic curves, the pressure and velocity distribution, and the static and total pressure values at impeller and volute exit. An analysis of the behavior of the pressure plots, and the loss and recovery of pressure in the volute was performed. The results indicated the characteristic curves, the pressure and velocity distribution were consistent with the turbomachinery theory. The pressure values showed the static pressure at volute exit was smaller than impeller exit for some flow rate. It caused the pressure recovery coefficient negative. This work indicated to be possible design a centrifugal fan applying the one-dimensional theory and optimize it with the CFD tool. La dinámica de fluidos computacional (CFD) es la tecnología más actual en el estudio del flujo de fluidos. Los métodos experimentales para predecir el rendimiento de las turbomáquinas implican un mayor consumo de tiempo y recursos financieros en comparación con el enfoque CFD. El propósito de este artículo es presentar el análisis de resultados de simulación CFD de un ventilador centrífugo. El rotor se calculó utilizando la teoría unidimensional y la voluta el principio de momento angular constante. Para la simulación se utilizó el software ANSYS-CFX. El modelo de turbulencia adoptado fue el SST. La simulación proporcionó las curvas características, la distribución de presión y velocidad, y los valores de presión estática y total en la salida del impulsor y la voluta. Se realizó un análisis del comportamiento de las gráficas de presión, y la pérdida y recuperación de presión en la voluta. Los resultados indicaron que la curva característica y la distribución de la presión fueron coherentes con la teoría de las turbomáquinas. Los valores de presión mostraron que la presión estática en la salida de la voluta fue menor que en la salida del rotor para algunos flujos. Esto provocó coeficientes de recuperación de presión negativos. Este trabajo indica que es posible diseñar un ventilador centrífugo aplicando la teoría unidimensional y optimizarlo con la herramienta CFD. A dinâmica de fluidos computacional (CFD) é a tecnologia mais atual no estudo de escoamento de fluidos. Métodos experimentais para prever o desempenho de turbomáquinas envolvem maior consumo de tempo e recursos financeiros em comparação com a abordagem CFD. A proposta deste artigo é apresentar a análise dos resultados de simulação CFD de um ventilador centrífugo. O rotor foi calculado utilizando a teoria unidimensional e a voluta o princípio do momento angular constante. Para a simulação foi utilizado o software ANSYS-CFX. O modelo de turbulência adotado foi o SST. A simulação forneceu as curvas características, a distribuição de pressão e velocidade, e valores de pressão estática e total na saída do rotor e da voluta. Uma análise do comportamento das parcelas de pressão, e da perda e recuperação de pressão na voluta foi realizada. Os resultados indicaram que a curva característica e a distribuição de pressão foram coerentes com a teoria das turbomáquinas. Os valores de pressão mostraram que a pressão estática na saída da voluta foi menor que a da saída do rotor para algumas vazões. Isto causou coeficientes de recuperação de pressão negativos. Este trabalho indica que é possível projetar um ventilador centrífugo aplicando a teoria unidimensional e otimizá-lo com a ferramenta CFD.

As a major component of any high rotating turbomachinery to withstand an axial load of the system while providing stability to the rotor, gas foil thrust bearing (axial bearing) should be designed and investigated accurately. The article presents sensitivity analysis and provides an optimum range of design parameters of a gas foil thrust bearing for which it has a maximum load-carrying capacity and low power loss using artificial intelligence techniques. The preliminary numerical model is tested by coupling the fluid flow and structural equations to predict the bearing performance. The standard non-dimensional Reynold’s equation is used to predict the pressure distribution of the fluid film. The obtained results from the numerical model are then validated with the experimental results available in the open literature. The article investigates the effect of various parameters like film thickness ratio, minimum film thickness, interface friction coefficients between top foil/bump foil and bump foil/bearing base and bump foil parameters on the load-carrying capacity, frictional torque, side leakage, and power loss. The results conclude four parameters (minimum film thickness, ratio of angular extent at wedging, angular extent of thrust pad, and rotational speed) have a significant effect on load carrying capacity and power loss as compared to others with optimized range. The results highlight the importance of numerical methodology, sensitivity analysis, and prediction capability of the artificial intelligence network.

Gas bearings are widely used in micro- and small turbomachinery. Because of the pursuit of high efficiency, turbomachinery adopts small clearance of rotor and stator. The gas bearing rotor system easily suffers from rub impact due to the inherently low damping and load capacity of gas film. Axial rub impact may lead to catastrophic failure of gas bearing rotor system. Previous work put emphasis on radial rub, and only a few papers researched on the axial rub impact by simulation method. In this paper, dynamic responses of full annular axial rub are investigated numerically and experimentally. A single span flexible rotor test rig is established to support this research. Dynamic characteristics of full annular axial rub of this gas bearing rotor system are obtained with finite element language-APDL. Dynamic characteristics within full speed range are experimentally researched based on the test rig. The dynamic behaviors are analyzed by means of waterfall diagrams, frequency spectrums, orbit trails, and vibration amplitude waveforms. During speed up, half speed whirl and gas film oscillation occur in radial direction. During speed down, the full annular axial rub between rotor thrust disk and gas bearing occurs. When lightly axial rub impact happens, the vibration patterns in the radial direction change barely, and 0 Hz component appears in the axial direction. When serious full annular axial rub impact happens, 0 Hz component occurs in both radial and axial directions and rotor orbit shows transverse motion in radial direction. These forms of dynamic characteristics can be effectively used to diagnose the full annular axial rub impact.

The use of radial bearings with segments on a self-generated hydrostatic suspension has been substantiated in order to satisfy the requirements for precision positioning of axes and efficiency of stabilization of shaft oscillations of power-consuming rotary machines. The methods of turbomachine dynamical analysis based on the modelling of the quasistationary processes in lubricating films that balance the harmonic loads on the rotor by redistributing the lubricant flow parameters in the bearing with integrated liquid dampers have been further developed. The complex approach for improving functional properties of turbomachine bearings on the basis of multicriteria optimization of hydraulic tracts parameters and lubrication system operating modes is presented.

Like any other turbomachinery, it is essential that the hydraulic behavior and performance of mixed-flow pumps are evaluated way in advance prior to manufacturing. Pump performance relies heavily on the proper design of the intake structure. Intake structures should be accurately designed in order to minimize and avoid unnecessary swirl and vortex formations. Ensuring the optimum performance condition as well as predicting how a particular intake structure affects the efficiency of the pump often requires either physical model studies or theoretical evaluations. Unfortunately, physical models are costly, time-consuming, and site-specific. Conversely, design and performance predictions using a theoretical approach merely gives performance values or parameters, which are usually unable to determine the root cause of poor pump performance. This study evaluates the viability of using Computational Fluid Dynamics (CFD) as an alternative tool for pump designers and engineers in evaluating pump performance. A procedure for conducting CFD simulations to verify pump characteristics such as head, efficiency, and flow as an aid for preliminary pump design is presented. Afterwards, a multiphase simulation using the VOF approach is applied to compare the fluid dynamics between four different pump intake structures. A full-sized CFD model of the pump sump complete with the pump’s active components was used for the intake structure analysis in order to avoid scaling issues encountered during the reduced-scale physical model test. The results provided a clear illustration of the hydraulic phenomena and characteristic curves of the pump. A performance drop in terms of reduction in TDH was predicted across the various intake structure designs. The CFD simulation of intake structure provided a clear insight on the varying degree of swirl, flow circulation, and effect on pump efficiency between all four cases.

sCO2 power cycles offer improved cycle efficiencies compared with traditional steam Rankine cycles. However, the turbomachinery required to support such a cycle does not exist at a commercial scale and requires development. This paper describes a new 10 MWe scale sCO2 turbine was developed and demonstrated in an sCO2 closed-loop recompression Brayton cycle. Since this turbine was developed for Concentrating Solar Power (CSP) applications, a target inlet temperature of over 700°C was chosen using funding from the US DOE SunShot initiative and industry partners. However, it can be applied to traditional heat sources such as natural gas, coal, and nuclear power. Traditional Rankine steam cycle thermal efficiencies are typically in the 35–40% range, but can be as high as 45% for advanced ultra-supercritical steam cycles. The sCO2 cycle can approach 50% thermal efficiency using externally fired heat sources. Furthermore, this cycle is also well suited for bottoming cycle waste heat recovery applications, which typically operate at lower temperatures. The high-power density and lower thermal mass of the sCO2 cycle results in compact, high-efficiency power blocks that can respond quickly to transient environmental changes and transient operation, a particular advantage for solar, waste heat, and ship-board applications. The power density of the turbine is significantly greater than traditional steam turbines and is comparable to liquid rocket engine turbo pumps. This paper describes the design and construction of the turbine and provides additional testing of the 10 MWe turbine in a 1 MWe test facility including a description of rotordynamics, thermal management, rotor aero and mechanical design, shaft-end and casing seals, bearings, and couplings. Test data for the turbine is included, as it achieves its operational goal of 715°C, 250 bara, and 27,000 rpm.

Stall flutter of long blades influences the operation safety of the large steam turbines in off-design conditions. As angles of attack are typically high, a partial or complete separation of the flow from the blade surface occurs. The prediction of stall flutter of turbine blades is a crucial task in the design and development of modern turbomachinery units and reliable design tools are necessary. In this work, aerodynamic stability of a linear turbine blade cascade is tested experimentally at high angle of attack +15°, Ma = 0.2 and the reduced frequency of 0.38. Controlled flutter testing has been performed in a travelling wave mode approach for the torsion with the motion amplitude of 0.5°. In addition, ANSYS CFX with SST k-ω turbulent model is used for URANS simulations of a full-scale computational domain. A separation bubble formed on suction surface near the leading edge has been found in CFD results for each blade. Excellent agreement between the experimental and numerical results in stability maps has been achieved for this case under investigation. This is encouraging and both experimental and numerical techniques will be tested further.

While turbocharging is a key technology for improving the performance and efficiency of internal combustion engines, the operating behavior of the turbocharger is highly dependent on the rotor temperature distribution as it directly modifies viscosity and clearances of the fluid film bearings. Since a direct experimental identification of the rotor temperature of an automotive turbocharger is not feasible at an acceptable expense, a combination of numerical analysis and experimental identification is applied to investigate its temperature characteristic and level. On the one hand, a numerical conjugate heat transfer (CHT) model of the automotive turbocharger investigated is developed using a commercial CFD-tool and a bidirectional, thermal coupling of the CFD-model with thermohydrodynamic lubrication simulation codes is implemented. On the other hand, experimental investigations of the numerically modeled turbocharger are conducted on a hot gas turbocharger test rig for selected operating points. Here, rotor speeds range from 64.000 to 168.000 rpm. The turbine inlet temperature is set to 600 °C and the lubricant is supplied at a pressure of 300 kPa with 90 °C to ensure practically relevant boundary conditions. Comparisons of measured and numerically predicted local temperatures of the turbocharger components indicate a good agreement between the analyses. The calorimetrically determined frictional power loss of the bearings as well as the floating ring speed are used as additional validation parameters. Evaluation of heat flow of diabatic simulations indicates a high sensitivity of local temperatures to rotor speed and load. A cooling effect of the fluid film bearings is present. Consequently, results confirm the necessity of the diabatic approach to the heat flow analysis of turbocharger rotors.

Pressure Gain Combustion (PGC) is considered a possible solution to increase gas turbine cycle efficiency, due to the lower entropy generation in the combustion process. However, the highly unsteady flow produced by PGC makes it more difficult to extract work from its exhaust gas. Any outlet restriction downstream of PGC, such as turbine blades, affects its flow field and may cause additional thermodynamic losses. The unsteadiness in the form of pressure, temperature and velocity vector fluctuations has a negative impact on the operation of conventional turbines. Therefore, evaluating early turbine design parameters for such applications is of great interest. Additionally, experimental measurements and data acquisition present researchers with challenges that have to do mostly with the high temperature exhaust of PGC and the high frequency of its operation. Numerical simulations can provide important insights into PGC exhaust flow and its interaction with turbine blades. In this paper, a Rotating Detonation Combustor (RDC) and a row of nozzle guide vanes have been modeled based on the data from literature and an available experimental setup at TU Berlin. Five guide vane configurations with different geometrical parameters have been modeled. URANS simulations were done for all guide vane arrangements to investigate the effect of solidity and blade type representing different outlet restrictions on the RDC exhaust flow. Total pressure loss and velocity fluctuation were computed upstream and downstream of the vanes. The results analzed the connection between total pressure loss and the vanes solidity and thickness to chord ratio. It is observed that more than 57% of the upstream velocity angle fluctuation amplitude was damped by the vanes. Furthermore, the area reduction was found to be the significant driving factor for damping the velocity angle fluctuations, whether in the form of solidity or thickness on chord ratio increment. A further study of the flow field details revealed that the vane passages act as convergent divergent nozzles in the unsteady flow field and no compression wave exists upstream. This RDC exhaust flow investigation is an important primary step from a turbomachinery standpoint, which provided details of blade behavior in such an unsteady flow field.

In the present work the evolution of the boundary layer over a low-pressure turbine blade is studied by means of direct numerical simulations. The set-up of the simulations follows the experiments by [1], aiming to investigate the unsteady flow field induced by the rotor-stator interaction. The free-stream flow is characterized by high level of free-stream turbulence and periodically impinging wakes. As in the experiments, the wakes are shed by moving bars modeling the rotor blades and placed upstream of the turbine blades. To include the presence of the wake without employing an ad-hoc model, we simulate both the moving bars and the stationary blades in their respective frames of reference and the coupling of the two domains is done through appropriate boundary conditions. The presence of the wake mainly affects the development of the boundary layer on the suction side of the blade. In particular, the flow separation in the rear part of the blade is suppressed. Moreover, the presence of the wake introduces alternating regions in the streamwise direction of high- and low-velocity fluctuations inside the boundary layer. These fluctuations are responsible for significant variations of the shear stress. The analysis of the velocity fields allows the characterization of the streaky structures forced in the boundary layer by turbulence carried by upstream wakes. The breakdown events are observed once positive streamwise velocity fluctuations reach the end of the blade. Both the fluctuations induced by the migration of the wake in the blade passage and the presence of the streaks contribute to high values of the disturbance velocity inside the boundary layer with respect to a steady inflow case. The amplification of the boundary layer disturbances associated with different spanwise wavenumbers has been computed. It was found that the migration of the wake in the blade passage stands for the most part of the perturbations with zero spanwise wavenumber. The non-zero wavenumbers are found to be amplified in the rear part of the blade at the boundary between the low and high speed regions associated with the wakes.

The following paper presents a new type of gas lubricated thrust bearing that utilizes additive manufacturing or also known as direct metal laser melting (DMLM) to fabricate the bearing. The motivation for the new bearing concept is derived from the need for highly efficient supercritical carbon dioxide (sCO2) turbomachinery in the mega-watt power range. The paper provides a review of existing gas thrust bearing technology, outlines the need for the new DMLM concept, and discusses proof of concept testing results. The new concept combines hydrostatic pressurization with individual tilting pads that are flexibly mounted using hermetic squeeze film dampers (HSFD) in the bearing-pad support. This paper describes the thrust bearing concept and discusses the final design approach. Proof-of-concept testing in air for a 6.8” (173mm) outer diameter thrust gas bearing was performed; with thrust loading, up to 1,500 lbs (6.67kN) and a thrust runner speed of 10krpm (91 m/s tip speed). The experiments were performed with a bent shaft resulting in thrust runner axial vibration magnitudes of 2.9mils (74microns) p-p and dynamic thrust loads of 270 lbs (1.2kN) p-p. In addition, force deflection characteristics and stiffness coefficients of the bearing system are presented for an inlet hydrostatic pressure of 380psi (2.62MPa). Results at 10krpm show that the pad support architecture was able to sustain high levels of dynamic misalignment equaling 6 times the nominal film clearance while demonstrating a unit load carrying capacity of 55psi (0.34Mpa). Gas-film force deflection tests portrayed nonlinear behavior like a hardening spring, while the bearing pad support stiffness was measured to be linear and independent of gas film thickness.

The present experimental study expands an ongoing effort to characterize the interactions of axial casing grooves (ACGs) with the flow in the tip region of an axial turbomachine. In recent work, we have tested a series of grooves with the same inlet geometry that overlaps with the rotor blade leading edge, but with different exit directions. Two geometries have stood out: The U grooves, which have an outflow in the negative circumferential direction (opposing the blade motion) are the most effective in suppressing stall, achieving as much as 60% reduction in stall flowrate, but cause a 2% decrease in efficiency around the best efficiency point (BEP). In contrast, the S grooves, which have an outflow in the positive circumferential direction, achieve a milder improvement in stall suppression (36%) but do not degrade the performance near BEP. This paper focuses on explaining these trends by measuring the flow in the tip region and within the U and S grooves. The stereo-PIV (SPIV) measurements are performed in the JHU refractive index matched facility, which allows unobstructed observations in the entire machine. Data has been acquired in two meridional planes that intersect with the grooves at different locations, and two radial planes (z, θ), the first coinciding with the blade tip, and the second, with the tip gap. For each plane, data has been acquired at fourteen rotor orientations relative to the grooves to examine the rotor-grooves interactions. At low flow rates, the inflow into both grooves peaks periodically when the blade pressure side (PS) faces the entrance (downstream side) to the grooves. This inflow rolls up into a large vortex that remains and lingers within the groove long after the blade clears the groove. The outflow depends on the shape of the groove. For the S groove, the outflow exits at the upstream end of the groove in the positive circumferential direction, as designed. In contrast, for the U grooves, the fast radially and circumferentially negative outflow peaks at the base of the U. The resulting jet causes substantial periodic variations in the flow angle near the leading edge of the rotor blade. Close to the BEP, the chordwise location of primary blade loading moves downstream, as expected. The inflow into the grooves occurs for a small fraction of the blade passing period, and most of the tip leakage vortex remains in the main flow passage. For the S grooves, the rotor-groove interactions seem to be minimal, with little (but not zero) inflow or outflow at both ends, and minimal changes to the flow angle in the passage. In contrast, for the U groove, the inflow into and outflow from the groove reverse direction (compared to the low flowrate trends), entering at the base of the U, and exiting mostly at its downstream end, especially when the blade is not near. The resulting entrainment of secondary flows from the groove into the passage are likely contributors to the reduced efficiency at BEP for the U grooves.

Conventional gas turbines are a very mature technology and performance improvements are becoming increasingly difficult and costly to achieve. Pressure Gain Combustion has emerged as a promising technology in this respect, due to the higher thermal efficiency of the respective ideal gas turbine cycles. Up to date, the majority of studies in the field has concentrated on the connection of the turbine to various types of pressure gain combustion systems. The current work focusses on the connection of an array of pulsed detonation tubes at the outlet of an axial compressor. An ideal 0-D plenum is assumed between the compressor outlet and the pulsed detonation tubes’ inlet. The tubes are simulated as time-dependent mass sinks in this plenum. A solution of the time-dependent mass conservation equations delivers the pressure variation in this ideal plenum for various combinations of its size, the tube number, the tube frequency, their firing pattern and their closing time. This pressure variation is subsequently used as a boundary condition in a numeric model of a compressor that can resolve very fast changes of its operational condition. The model is based on the solution of the time-dependent 1-D Euler equations with source terms for the blade forces and the work exchange with the fluid along the compressor stages. These source terms are computed from the operational map of the compressor. The influence of the aforementioned five parameters (number of tubes, frequency, closing time, firing pattern and plenum size) on the compressor operational stability and the flow in its stages is studied in detail. The aim is to benchmark the design of a plenum that results in the lowest possible compressor outlet pressure fluctuation without becoming too large. At the same time, the pressure fluctuations and their propagation along the compressor stages are analyzed.

Flutter stability is a dominant design constraint of modern gas and steam turbines. Thus, flutter-tolerant designs are currently explored, where the resulting vibrations remain within acceptable bounds. In particular, friction damping has the potential to yield Limit Cycle Oscillations (LCOs) in the presence of a flutter instability. To predict such LCOs, it is the current practice to model the aerodynamic forces in terms of aerodynamic influence coefficients, derived for some normal modes of the linearized structural model and fixed oscillation frequency. However, this approach neglects that both the nonlinear contact interactions and the aerodynamic stiffness cause a change in the deflection shape and the frequency of the LCO. This, in turn, may have a substantial effect on the aerodynamic damping. The goal of this paper is to assess the technical importance of these neglected interactions. To this end, a state-of-the-art aero-elastic model of a low pressure turbine blade row is considered, undergoing nonlinear frictional contact interactions in the tip shroud interfaces. The LCOs are computed with a fully-coupled harmonic balance method, which iteratively computes the Fourier coefficients of structural deformation and conservative flow variables, as well as the a priori unknown frequency. The coupled algorithm was tested for various combinations of harmonics in both domains and found to provide excellent computational robustness and efficiency. Moreover, a refinement of the conventional energy method is developed and assessed, which accounts for both the nonlinear contact boundary conditions and the linearized aerodynamic influence. It is found that the conventional energy method may not predict a limit cycle oscillation at all while the novel approach presented here can. Furthermore the refined energy method provides deep understanding of the nonlinear aero-elastic interactions.

Intentional mistuning is a common procedure to decrease the uncontrolled vibration amplification effects of the (unavoidable) random mistuning, and to reduce the sensitivity to it. The idea is to introduce an intentional mistuning pattern that is small, but much larger than the existing random mistuning. The frequency of adjacent blades is moved apart by the intentional mistuning, reducing the blade-to-blade coupling and, thus, the effect of the random mistuning. In order to clearly show the action mechanisms of intentional mistuning, we focus in this work in a quite simple configuration: forced response of a blade dominated modal family in a mistuned rotor with linear material damping. The problem is analysed using the asymptotic mistuning model methodology. A more reduced order model is derived that allows us to understand the relevant parameters behind the effect of intentional mistuning, and gives a simple expression for the estimation of its beneficial effect. The results from the reduced model are checked against detailed FEM simulations of two mistuned rotors.