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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.

Distributed aircraft propulsion has renewed the interest in power-dense, high-efficiency power packs. Ceramic turbomachinery could be a major enabler, although no successful design has been achieve...

The current generation of axial turbomachines are the culmination of decades of experience, and detailed understanding of the underlying flow physics has been a key factor for achieving high efficiency and reliability. Driven by advances in numerical methods and relentless growth in computing power, computational fluid dynamics has increasingly provided insights into the rich fluid dynamics involved and how it relates to loss generation. This article presents some of the complex flow phenomena occurring in bladed components of gas turbines and illustrates how simulations have contributed to their understanding and the challenges they pose for modeling. The interaction of key aerodynamic features with deterministic unsteadiness, caused by multiple blade rows, and stochastic unsteadiness, i.e., turbulence, is discussed. High-fidelity simulations of increasingly realistic configurations and models improved with help of machine learning promise to further grow turbomachinery performance and reliability and, thus, help fluid mechanics research have a greater industrial impact. Expected final online publication date for the Annual Review of Fluid Mechanics, Volume 54 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Dry gas seals represent a significant advancement in turbo machinery due to their ability to handle high pressures and speeds without the use of external sealing fluids, such as oil or water, thus reducing contamination and increasing reliability. Despite their widespread use, internal working mechanisms are not fully understood to date, in particular regarding fluid film thickness prediction, which is an essential component of the seal design. The axial deflection of the rotating and stationary rings in a dry gas seal affects the development of the fluid film formed between the ring faces of the seal, influencing the performance of the seal during its operation, as well as leakage of the seal when it is at rest. The hydrodynamic and hydrostatic pressure fields of the fluid film, together with temperature gradients in the rings, induce axial deflection of these components. This in turn modifies the pressure field developed in the film. This paper focuses on establishing a methodology to couple the deformation field and the dynamic behavior of the fluid film (pressure and temperature fields) through numerical computations. Analytical relationships are employed to obtain the thermo-elastic deflection of the seal rings in the axial direction and this distortion is used in the numerical methodology to accelerate the prediction of the seal behavior. The coupled seal ring-fluid film dynamic system with 11° and 15° spiral angle is stable because the axial deflection calculated from numerical analysis produces a converging radial taper in the direction of the flow (producing a net opening force). An important result of this work is that the predicted magnitude of the axial deflection (as a result of pressure and temperature effects) under thermal and pressure loads on the stationary and rotating rings is smaller but of the same order of magnitude as the fluid film thickness.

Rotating shaft–disk–blade (RSDB) system is one of the most important parts of turbomachinery, such as aero-engine, gas turbine and power plant. The coupling vibration of RSDB system with blade crack is vital for the blade health monitoring and crack detection of rotating blade. This study aims at addressing the dynamic modeling and steady-state coupling vibration mechanism of RSDB system with blade crack. First and foremost, on the basis of the stress state at crack section, an improved analytical breathing crack model (modified stress-based breathing crack model, MSBCM) for rotating blade is proposed. The validity of the proposed breathing crack model is verified by comparing the results obtained by MSBCM, finite element contact crack model and conventional analytical crack models. The comparative results suggest that MSBCM is of high fidelity and behaves best among the analytical crack models. Subsequently, a comprehensive dynamic model of the coupling vibration for RSDB system with blade crack is formulated on the basis of continuum beam theory and Lagrange equation. The shaft bending, shaft torsion, blade bending and blade radial deformation are comprehensively considered in this model. The validity of the proposed dynamic model is verified through comparison with finite element simulation and experimentation results. By introducing the proposed MSBCM, the dynamic coupling vibration model of the RSDB system with blade crack is formulated. At last, the steady-state coupling vibration mechanism of two typical structures for RSDB system is comprehensively investigated. It is suggested that the shaft torsional vibration is much more sensitive to blade crack than the shaft bending vibration be, which indicates that the vibration features of shaft torsional vibration may offer indicators for the presence of blade crack.

Turbine blade failures are among the leading causes of steam turbine failure. Failure types typically include cracking, rubbing, blade fouling, and foreign object damage. There is currently a range of non-destructive testing methods used to detect damage at the blade-disk attachment zone, all of which involve disassembling of the blade from the disk for periodic inspection. Evidence indicate that a method to detect damage at the blade-disk attachment zone using a non-contact, non-destructive in-situ off-line modal-based structural health monitoring technique could be useful under some circumstances. Such a technique would have the advantage of eliminating the necessity to disassemble blades during inspection. This would result in significant cost savings. Also, defects associated with the disassembly and reassembly of blades would be avoided. Thus, the aim of this study was to develop a modal-based turbomachinery blade disk attachment inspection technique. Modal parameters were acquired from a robust experimental modal analysis of freely supported low-pressure steam turbine blade-disk segment assemblies. Artificial single-location cracks were intentionally introduced into the turbine blades by cutting a 1 mm thickness notch at three probable damage locations, namely, at the upper pinhole on the leading-edge pressure side, above the root at the base of the aerofoil on the leading-edge and on the trailing-edge. In this work, a finite element analysis of the bladed disk segment assemblies was carried out with and without damage. To validate the reliability of the numerical models, the numerical results were correlated with the measured values, the results of which showed a strong correlation. Finally, a parametric study was conducted in which various healthy and damaged blade-disk cases were systematically investigated. This was done to examine the sensitivity of the blade natural frequency to damage. The artificial damage above the root was found to cause the largest changes in natural frequency. These changes were even more pronounced for assemblies with two blades. Receiver operating characteristic curves were used to assess the discriminatory ability of the results. Each damage case was found to be unique and therefore identifiable from its corresponding healthy case.

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

As a promising metalwork processing technology, electromagnetic induction heating (EMIH) method has been applied in dealing with bolted flange joints in turbomachinery. In this study, a 3-D finite element model of electromagnetic induction heating system for the bolted flange joint is established, and the specific governing equations are derived based on Maxwell’s principle. The alternately-coupled magneto-thermal analysis is carried out considering temperature-dependent material properties to obtain the temperature distribution, followed with the uncoupled thermal-mechanical analysis to acquire the axial stress and deformation in EMIH process. The magnetic induction intensity mainly concentrates at the inner wall region, attenuates seriously along the radial direction, and reduces to almost zero at the outer wall. Due to the skin effect, the heat transfers radially and axially outward, indicating a diamondlike-shaped development from the center to the surrounding region. The axial stress with and without initial pretension are also discussed respectively. Then the corresponding experiments are introduced and carried out to validate the reliability of numerical simulation results. By comparing the results of the center point of inner surface and outer surface, the numerical simulation is proved reliable with a 5∼10% reasonable deviation. Further, the induction heating process has been improved through the optimization method based on pattern search algorithm. By adopting the stepped input current density optimized in the study, the optimal thermal stress tends to be constant and the final heating time reduces by 20.5% in the safe range of stress.

The question of the difference mesh refinement degree influence on the results of calculation of the three-dimensional viscous gas flows in the flow parts of turbomachines using the RANS flow models and second order numerical methods is considered. Calculations of flows for a number of turbine and compressor grids on successively refining grids have been performed. We used H-type grids with approximate orthogonalization of cells in the boundary layer. The calculations were carried out using a CFD solver F with the use of an implicit ENO scheme of the second order, a local time step, and a simplified multigrid algorithm. When calculating the flow on fine grids, the following were used: convergence acceleration tools implemented in the solver; truncation of the computational domain with subsequent distribution of the results based on the symmetry property; the computational domain splitting into parts and computations parallelizing. Comparison of the obtained results is carried out, both in terms of qualitative resolution of the complex structure of three-dimensional flows, and in terms of quantitative assessment of losses. Grid convergence was estimated in two ways. In the first, the characteristic two-dimensional distributions of parameters obtained on different grids were visually compared. The purpose of such comparisons was to evaluate the sufficient degree of solution of both the general structure of the flow in grids and its features, namely, shock waves, contact discontinuities, separation zones, wakes, etc. The second estimation method is based on the grid convergence index (GCI). The GCI calculated from the three-dimensional density field was considered in this paper. It is concluded that for scientific research requiring high accuracy of calculations and detailing of the structure of a three-dimensional flow, very fine difference meshes with the number of cells from 106 to 108 in one blade-to-blade channel are needed, while for engineering calculations, under certain conditions, it is sufficient to use meshes with the number of cells less than 1 million in one blade-to-blade channel.

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 operational features determining innovative approaches to the design of space nuclear energy installations are analyzed. It is shown that there is no alternative to space nuclear energy for solving potential problems and the main directions of its use are determined. The main results obtained at NIKIET on the development of a nuclear rocket motor and space nuclear energy installations with turbomachine energy conversion are presented. A comparative analysis with the results obtained in the US space program is given.

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.

Hybrid solid oxide fuel cells (SOFC) cycles of varying complexity are widely studied for their potential efficiency, carbon recovery and co-production of chemicals. This study introduces an alternative de-coupled fuel cell-gas turbine hybrid arrangement that retains the high efficiency thermal integration of a topping cycle without the high temperature heat exchanger of a bottoming cycle. The system utilizes a solid-state oxygen transport membrane to divert 30%–50% of the oxygen from the turbine working fluid to the intermediate temperature SOFC. Thermodynamic modeling delineates design trade-offs and identifies a flexible operating regime with peak fuel-to-electric efficiency of 75%. Co-production of electricity and high purity hydrogen result in net energy conversion efficiencies greater than 80%. The potential to retrofit existing turbine systems, particularly micro-turbines and stand-by ‘peaker’ plants, with minimal impact to compressor stability or transient response is a promising pathway to hybrid fuel cell/turbine development that does not require turbomachinery modification.

Dry friction is widely incorporated in turbomachinery, in the form of under-platform dampers, to limit vibrations at resonance and reduce risks of high-cycle fatigue failures. Most of the test rigs that were used to investigate the behavior of under-platform dampers aim at evaluating the damper performance in terms of reduction of forced-response amplitude in blades. This approach could be insufficient to understand local nonlinearities in the contact and the influence of dampers on blade dynamics. A recently developed test rig provides the authors with an unprecedented set of information. It is capable to measure contact forces and relative displacements between dampers and blade in addition to the overall blade dynamic response. This controlled environment, together with an effective model of the blade/dampers system, is used to provide an insight into the subject of model validation. The presented experimental and numerical study of the damper is used to highlight the relevance of an accurate representation of the constraints induced by friction contacts and to discuss the adequacy of state-of-the-art contact models.

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.

This paper presents the use of a conventional computational-fluid-dynamics-based throughflow method to model the effects of a bypass fan in a propulsion system (for example, nacelle) under the rest...

Turbomachinery blisks have very low damping and, for this reason, they require devices such as ring dampers to mitigate excessive vibrations. Ring dampers rely on the relative motion between a ring...

The vibration caused blade High Cycle Fatigue (HCF) is seriously affects the safety operation of turbomachinery especially for aero-engine. Thus, it is crucial important to identify the blade vibration parameters and then evaluate the dynamic stress amplitude. Blade Tip Timing (BTT) method is one of the promising method to solve these problems. While, it need a high resolution Once Per Revolution (OPR) signal which is difficult to get for the aero-engine. Here, a Coupled Vibration Analysis (CVA) method for identifying blade vibration parameters by a none OPR BTT is proposed. The method assumes that every real blade has its own vibration performance at a given speed. Whereby, it can take any blade as the reference blade, and the other blades using the reference blade as the OPR for vibration displacement calculating and further parameter identifying. The proposed method is validated by numerical model. Also, experimental studies are carried out on a straight blade and a twisted three dimensional blade test rig as well as a large industrial axial compressor respectively. The results show that the proposed method can accurately identify the blade synchronous vibration parameters and quantitatively evaluate the mistuning in bladed disks, which lays a foundation for the reliability improvement of aero-engine.

An aeroelastic modeling capability of a flexible aircraft with gas turbine engines is developed using a computational fluid dynamics tool as an integration platform. The new modeling capability all...

Steady computational fluid dynamics solvers based on the Reynolds-averaged Navier–Stokes equations are the primary workhorses for turbomachinery aerodynamic analysis due to their good engineering a...

A model has been developed to characterize the cavitation phenomenon in dredging centrifugal pumps. The operating parameters of a cutter type dredger: swing speed, dredging depth, and inclination, impeller rpm, as well as slurry characterizations such as density and velocity, are introduced, to determine how they influence the operation of the dredge pump. The geometric characterization of the hydraulic transport system of the dredger was performed. With the dredge operationaĺs parameters, along with the geometric characterization, the pump is modeled in CFD turbomachinery software. To validate the operational points, the CFD model considers the RNG k-ε model and the cavitating-multiphase flow. Through the central composite experiment design, the operating conditions range of the dredger is determined, in which the pump can operate and cavitate. This allows validating the model for different operational points. Finally, multiple regression shows the influence of each of the variables in the response obtained. Furthermore, the regression allows an understanding that operating conditions of the dredger must be adjusted to mitigate the phenomenon of cavitation in the dredging process. Keywords: Cavitation, Centrifugal pump, CFD, Dredging, Slurry

An aerodynamic inverse design method, which is used in compressors, is introduced in this paper. This inverse design method is based on the exact solution of the local Riemann problem on moving blade surfaces. Furthermore, an improved relaxation factor is added to control the induced velocity for reasonable deformation sizes in different cases. The viscous flow analysis and the inverse design are integrated in the computational fluid dynamics software ANSYS Fluent using the dynamic mesh user-defined function, which reduces the time spent on remeshing the computational domain. A compressor cascade is taken to illustrate the effect of this inverse design method. Using the compressor model, the case of a different loading pattern design under a high subsonic flow regime and the case of a loading smooth design under a transonic flow regime have proved the capability of this inverse design method to realize the prescribed pressure loading distribution.

Electrical discharge machining (EDM) is regarded as the most competitive solution for the machining of high-aspect ratio cavities with strict requirements in surface quality and accuracy. The diversity of applications ranges from the plastic injection mold industry to the manufacturing of turbine components. The cooling holes in vanes and blades and the seal slots in nozzle guide vanes (NGV) are demanding geometries in the aerospace sector usually processed by EDM. The nature of the material removal in EDM, developed without any contact with the part, is considered a major advantage when difficult to manufacture superalloys are involved. However, in high-aspect ratio cavities, due to debris accumulation in the narrow gap, the machining stability is limited with the machining depth. This productivity limitation has been a matter of industrial and scientific research. Considering that the key requirements in aerospace industry are quality and machining performance, this study proposes different machining strategies with the objective of enhancing the productivity of high-aspect ratio slots in Nickel base C1023 super-alloy. Results demonstrate that planetary motion of electrode during the machining process is a promising industrial solution for enhancing machining productivity of the slots machining in the lateral faces of NGV turbine components.

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.

Proceedings of ASME Turbo Expo 2021: Turbomachinery Technical Conference and Exposition : June 7-11, 2021, virtual, online. - Volume 7: Industrial and cogeneration, manufacturing materials and metallurgy ASME Turbo Expo 2021, online, 7 Jun 2021 - 11 Jun 2021; New York, N.Y. : The American Society of Mechanical Engineers GT2021-59562, V007T17A012, 1-9 (2021). doi:10.1115/GT2021-59562, Published by The American Society of Mechanical Engineers, New York, N.Y.

A gas turbine is a turbomachine composed of a compressor part, a part with heat supply to the compressed gas and a turbine part in which the hot gas expands. The present chapter discusses gas turbines for mechanical power ­generation. These are machines with an outgoing shaft, meant to drive a load. The largest market sector of such machines is electrical power generation, but machines for driving compressors and pumps in industrial plants and for driving large vehicles and ships also are examples. We discuss the working principles of the components of power gas turbines in the present chapter. As electric power generation is the largest sector of application, we choose components of such machines for illustrations. The main purpose of the chapter is the discussion of the overall performance of power gas turbines. Performance analysis is a matter of thermodynamic modelling and is not strongly linked to a particular application.

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.

The Covid-19 pandemic has changed the university education, with most teaching moved off campus and students learning online or remote at home, but a cornerstone of undergraduate engineering education has been a big challenge, namely the laboratory classes. As the engineering and education communities continue to adapt to the realities of a global pandemic, it is important to recognize the importance of the laboratory-based courses. In order to address to this situation, an ambitious approach is taken to recreate the laboratory experience entirely online with the help of the digital twins of the fluid mechanics, thermodynamics, and turbomachinery laboratory experiments. Laboratory based undergraduate courses such as EFPLAB1, EFPLAB2 (Energy; Fluid and Process Laboratory 1 & 2) and EFPENG (Energy; Fluid and Process Engineering) are important parts of the “mechanical engineering” and “energy systems engineering” curricula of the Lucerne University of Applied Sciences (HSLU) in Switzerland. Each course mentioned above include six different laboratory experiments about fluid mechanics, thermodynamics, turbomachinery, energy efficiency, and energy systems, including mass- and energy flow balances in energy systems. During the Covid-19 pandemic, it was necessary to adapt to the new environment of remote learning courses and modify the laboratory experiments so that they can be carried out online. The approach was developing digital twins of each laboratory experiment with web applications and providing an environment together with supporting videos and interactive problems so that the laboratory experiments can be carried out remotely. A digital twin is a digital representation of a physical system, e.g., the test rig. It may contain a collection of various digital models with related physical equations and solutions, information related to the operation of the test rig, including 2D or 3D models, process models, sensor data records, and documentation. Ideally, all quantities and attributes that could be measured or observed from the real experiment should be accessible from its digital twin. The digital twin not only reproduces the experimental setup in the laboratory but also helps to improve the knowledge related to the theory and concepts of the laboratory experiments. One major advantage of the digital twin is that the number and range of the parameters, which can be manipulated or varied, is larger in comparison to the actual testing in the laboratory. This paper explains the development of the digital twins (web applications) of the laboratory experiments and provides information about the selected experiments such as potential vortex, linear momentum equation, diffuser flow, radial compressor, fuel cell, and pump test rig with the measurement of pump characteristics. A remote or distance learning has many hurdles, one of the largest being how to teach hands-on laboratory courses outside of an actual laboratory. The experience at the Lucerne University of Applied Sciences showed that teaching online labs using the digital twins of the laboratory experiments can work and the students can take part in remote laboratories that meet the learning outcomes and objectives as well as engage in scientific inquiry from a distance.

Rotating blade is one of the most important components for turbomachinery. Blade crack is one of the most common and dangerous failure modes for rotating blade. Therefore, the fault mechanism and feature extraction of blade crack are vital for the safety assurance of turbomachinery. This study is aimed at the nonlinear dynamic model of rotating blade with transverse crack and the prior feature extraction of blade crack faults based on the vibration responses. First and foremost, a high-fidelity breathing crack model (HFBCM) for rotating blade is proposed on the basis of criterion for stress states at crack section. Since HFBCM is physically deduced from the perspective of energy dissipation and the coupling between centrifugal stress and bending stress is considered, the physical interpretability and the accuracy of the crack model are enhanced comparing with conventional models. The validity of the proposed HFBCM is verified through the comparison study among HFBCM, conventional crack models, and finite element-based contact crack model (FECCM). It is suggested that HFBCM behaves best among the analytical models and matches well with FECCM. With the proposed HFBCM, the nonlinear vibration responses are investigated, and four types of blade crack detection indicators for rotating blade and their quantification method are presented. The numerical study manifests that all these indicators can well characterize the occurrence and severity of crack faults for rotating blade. It is indicated that these indicators can serve as the crack-monitoring indexes.

The coupling between different components of a turbomachinery is becoming more widely studied especially by use of computational fluid dynamics. Such simulations are of particular interest especially at the interface between a combustion chamber and a turbine, for which the prediction of the migration of hotspots generated in the chamber is of paramount importance for performance and life-duration issues. Despite this need for fully integrated simulations, typical turbomachinery simulations however often only consider isolated components with either time-averaged constant value, radial profile or least frequently two-dimensional maps imposed at their inlet boundaries preventing any accurate two-way coupling. The objective of this study is to investigate available solutions to perform isolated simulations while taking into account the effect of multicomponent coupling. Investigations presented in the paper focus on the full aero-thermal combustor-turbine interaction research (FACTOR) configuration. The first step of the proposed method is to record conservative variables solved by the large-eddy simulation (LES) code at the interface plane between the chamber and the turbine of a reference simulation. Then, using the spectral proper orthogonal decomposition (SPOD) method, the recorded data is analyzed and can be partially reconstructed using different numbers of frequencies. Using the partial reconstructions, it is then possible to replicate a realistic inlet boundary condition for isolated turbine simulations with both velocity and temperature fluctuations, while reducing the storage cost compared to the initial database. The integrated simulation is then compared to the isolated simulations as well as against simulations making use of averaged quantities with or without synthetic turbulence injection at their inlet. The isolated simulations for which the inlet condition is reconstructed with a large number of frequencies show very good agreement with the fully integrated simulation compared to the typical isolated simulation using average quantities at the inlet. As expected, decreasing the number of frequencies in the reconstructed signal deteriorates the accuracy of the resulting signal compared to the full recorded database. However, isolated simulations with a low number of frequencies still perform better than standard boundary conditions, especially from an aero-thermal point of view.

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 technology management methods and the “technology foresight” allow organizations and stakeholders in a particular market/sector to create an advantage out of technological breakthroughs, sustain and expand technological competitiveness, and identify and evaluate new technological options. Several concepts are used depending mainly on the actual status of an evaluated technology. To identify the status of the supercritical carbon dioxide (sCO2) power generation technologies, an extensive “technology exploration” task was performed by creating a technology profile through collecting a database. This allowed for creating technological forecasts “scenario approach” for the sCO2 power cycles. In this article, the sCO2 power technology is explored, evaluated in relation to current commercial competitive power generation technologies, and forecasted to give an insight into future trends of the novel sCO2 power cycle in the future market. The outcome is the analysis of qualitative and quantitative data of the sCO2 technology for short- to long-term forecasts, which could help identify the economic and market value of the sCO2 power cycle. Three possible market scenarios were identified and combined with a survey distributed among experts to assess different market penetration levels of the sCO2 technology.

The field of turbomachinery is undergoing major advances in aeroelasticity and this chapter provides an overview of these new developments in the key enabling methodology of unsteady aerodynamic modeling. Also see the earlier discussions in chapters “Aeroelasticity in Turbomachines” and “Modeling of Fluid-Structure Interaction.”

Boundary layer ingestion (BLI) concepts have become a prominent topic in research and development due to their increase in fuel efficiency for aircraft. Virginia Tech has developed the StreamVane™, a secondary flow distortion generator, which can be used to efficiently test BLI and its aeromechanical effects on turbomachinery. To ensure the safety of this system, the complex vanes within StreamVanes must be further analyzed structurally and aerodynamically. In this paper, the induced strain of two common vane shapes at three different operating conditions is computationally determined. Along with these predictions, the aerodynamic damping of the vanes is calculated to predict flutter conditions at the same three operating points. To achieve this, steady computational fluid dynamics (CFD) calculations are done to acquire the aerodynamic pressure loading on the vanes. Finite element analysis (FEA) is performed to obtain the strain and modal response of the StreamVane structure. The mode shapes and steady CFD are used to initialize an unsteady CFD analysis, which acquires the aerodynamic damping results of the vanes. The testcase used for this evaluation was specifically designed to overstep the structural limits of a StreamVane, and the results provide an efficient computational method to observe flutter conditions of stationary systems.

The simulation models used in the design process of modern turbo-machines are becoming increasingly complex. Nevertheless, the steady-state RANS approach is still the mostly used method for CFD computations. However, detailed flow information is more and more required for further improving the performance and extend the operating range. Turbulence modeling has becoming therefore a key issue in this context. The increased computer power already available would enable the use of more sophisticated turbulence models than standard two equation ones, such as SST k-omega and k-epsilon. These, despite their shortcomings, are still predominant in the field, since more advanced models often lead to numerical instabilities in the simulations. The most important shortcomings can be related to either boundary layer effects or mixing process in the channels. In order to improve the predictions considering boundary layer effects, like impingement or large pressure gradients in flow direction, various derivations of four equations models were investigated. Using an additional transport equation for the wall normal Reynolds-stress component and an elliptic equation for near-wall effects, they improve the results for this kind of flows. Considering the accurate prediction of mixing processes, like (1) the interaction of tip-clearance vortices with the main flow or (2) off-design conditions, the focus was oriented to the anisotropy present in the turbulent structures. Standard models are often not sufficient to predict accurately vortices, which can have a huge impact on the performance, since based on the assumption of isotropic turbulence. Accordingly, they tend to dissipate and diffuse the vortices too quickly. Improved models, which take the anisotropic nature of the Reynolds-stresses into account, can help in this context. The models can thereby introduce the additional anisotropy via an explicit algebraic expression, or model directly the transport equations for the Reynolds-stresses. In order to improve the predictions using advanced turbulence models a particularly robust framework based on a pressure-based fully coupled approach was used. The goal of this work is the development and testing of improved models for the application in turbo-machinery. The focus lies thereby on near-wall behavior and mixing / vortex dissipation. The assessment of the models is exemplarily used on the centrifugal compressor open-case Radiver with vaned diffuser.

Μεγάλη προσπάθεια γίνεται τα τελευταία χρόνια για την ανάπτυξη αποδοτικών μηχανών μετατροπής ενέργειας. Τα κίνητρα για αυτή την προσπάθεια είναι κυρίως η ολοένα αυξανόμενη ζήτηση για ηλεκτρική ενέργεια, η εξάντληση των κοιτασμάτων ορυκτών καυσίμων καθώς και η μόλυνση του περιβάλλοντος από εκπομπές αέριων ρύπων. Μια τεχνολογία που φαίνεται ότι θα συμβάλει σημαντικά στην διαμόρφωση του ενεργειακού τομέα στο μέλλον, είναι οι μικροστρόβιλοι. Οι μικροστρόβιλοι λόγω των πλεονεκτημάτων που παρουσιάζουν μπορούν να χρησιμοποιηθούν σε εφαρμογές κατανεμημένης παραγωγής ηλεκτρικής ενέργειας, smart grids, υβριδικά συστήματα και συστήματα συμπαραγωγής.Αντικείμενο της παρούσας διατριβής είναι η μελέτη εφαρμογών μικροστροβίλων, τόσο υπολογιστικά όσο και πειραματικά. Οι υπολογιστικές δραστηριότητες περιλαμβάνουν κυρίως την μελέτη υβριδικών συστημάτων τύπου SOFC-GT (Solid Oxide Fuel Cell – Gas Turbine). Στα συστήματα αυτά γίνεται συνδυασμός ενός μικροστροβίλου και μιας γεννήτριας τύπου SOFC, η οποία λειτουργεί σε συνθήκες υπερπίεσης (υπετροφοδοτείται). Το καύσιμο αντιδρά ηλεκτροχημικά στις κυψέλες καυσίμου SOFC (που υποκαθιστούν το θάλαμο καύσης του μικροστροβίλου) και παράγει ηλεκτρική ενέργεια μαζί με θερμότητα. Η θερμότητα χρησιμοποιείται από το μικροστρόβιλο για την παραγωγή επιπλέον ηλεκτρικής ενέργειας. Τα συστήματα αυτά έχουν υψηλούς βαθμούς απόδοσης και θεωρούνται ως μια εναλλακτική επιλογή των συμβατικών συστημάτων ηλεκτροπαραγωγής.Για την μοντελοποίηση των υβριδικών συστημάτων χρησιμοποιήθηκε ένα λογισμικό γενικής χρήσης (AspenPlus). Ξεκινώντας με μια προτεινόμενη μέθοδο από την διαθέσιμη βιβλιογραφία, έγιναν προσθήκες νέων στοιχείων με σκοπό την δημιουργία ενός βελτιωμένου μοντέλου. Επιπλέον, αναπτύχθηκαν μοντέλα για την προσομοίωση των στροβιλομηχανών στο λογισμικό γενικής χρήσης, ιδιαίτερα σε μερικό φορτίο, για πρώτη φορά σε αυτό το περιβάλλον. Στην παρούσα διατριβή εξετάζονται σχεδιασμοί υβριδικών συστημάτων βασιζόμενοι σε εμπορικά διαθέσιμους μικροστροβίλους και σε μια επιτυχημένη γεννήτρια τύπου SOFC η οποία δοκιμάστηκε σε αρκετά πιλοτικά προγράμματα διεθνώς. Αναπτύχθηκαν μοντέλα και βαθμονομήθηκαν με βάση πειραματικά δεδομένα από την βιβλιογραφία. Μελετήθηκε η συμπεριφορά σε συνθήκες πλήρους και μερικού φορτίου καθώς και η επίδραση σημαντικών λειτουργικών παραμέτρων στις επιδόσεις των υβριδικών συστημάτων. Τα αποτελέσματα έδειξαν ότι τα συστήματα αυτά μπορεί να οδηγήσουν σε υψηλούς βαθμούς απόδοσης, εφόσον γίνει κατάλληλη βελτιστοποίηση στο σχεδιασμό του συστήματος καθώς και στο μέγεθος του μικροστροβίλου. Η προηγούμενη εμπειρία που αποκτήθηκε οδήγησε σε μια μεθοδολογία για την βελτιστοποίηση των στροβιλομηχανών σε υβριδικά συστήματα SOFC-GT. Η μεθοδολογία περιλαμβάνει δυο βήματα. Στο πρώτο γίνεται μια παραμετρική ανάλυση για να αποτιμηθεί το λειτουργικό πεδίο του συστήματος και στο δεύτερο, λαμβάνοντας υπόψη τις πληροφορίες του πρώτου βήματος, υπολογίζονται οι βέλτιστες γεωμετρίες για τον συμπιεστή και τον στρόβιλο χρησιμοποιώντας in-house κώδικες που αναπτύχθηκαν για αυτό τον σκοπό. Τα αποτελέσματα έδειξαν σημαντική βελτίωση των επιδόσεων του συστήματος σε όλο το εύρος λειτουργίας του. Η υποδομή που δημιουργήθηκε επιτρέπει τη μελέτη επιπλέον σχεδιαστικών επιλογών, με χωριστή επιλογή συμπιεστή και στροβίλου, διαφορετικού τύπου συμπιεστή κτλ, όπως και διαφορετικών επιλογών στο σύστημα ελέγχου. Οι πειραματικές δραστηριότητες που έγιναν στα πλαίσια αυτής της διατριβής, αφορούν ένα μικροστρόβιλο τύπου turbojet. Παρουσιάζεται η εμπειρία που αποκτήθηκε από την ανάπτυξη ενός μοντέλου για την προσομοίωση της συμπεριφοράς του σε μόνιμες συνθήκες λειτουργίας. Τα αποτελέσματα έδειξαν ότι κάποιες μετρήσεις που λαμβάνονται από την λειτουργία της μηχανής δεν είναι αντιπροσωπευτικές της μέσης τιμής που επικρατεί σε κάθε διατομή. Ωστόσο η απόκλιση είναι συστηματική και επαναλήψιμη με αποτέλεσμα να μπορούν να υιοθετηθούν διαδικασίες διόρθωσης των μετρήσεων. Εκτός από την μελέτη σε μόνιμες συνθήκες λειτουργίας, μελετήθηκε και η μεταβατική λειτουργίας της μηχανής μέσω ενός μοντέλου που αναπτύχθηκε για αυτό το σκοπό. Τα αποτελέσματα των προσομοιώσεων είναι σε αρκετά καλή συμφωνία με τα πειραματικά δεδομένα. Η εμπειρία που αποκτήθηκε από το μεταβατικό μοντέλο λειτουργίας αναμένεται να αξιοποιηθεί για την ανάπτυξη μεταβατικού μοντέλου λειτουργίας για τα συστήματα SOFC-GT, προκειμένου να μελετηθεί καλύτερα το σύστημα ελέγχου για προστασία της συστοιχίας SOFC από αιχμές πίεσης, surge, αποσυσμπίεση κτλ.

Compressible flows are encountered in many applications in Aerospace and Mechanical engineering. Some examples are flows in nozzles, compressors, turbines and diffusers. In aerospace engineering, in addition to these examples, compressible flows are seen in external aerodynamics, aircraft and rocket engines. In almost all of these applications, air (or some other gas or mixture of gases) is the working fluid. However, steam can be the working substance in turbomachinery applications. Thus, the range of applications in which compressible flow occurs is quite large and hence a clear understanding of the dynamics of compressible flow is essential.

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.

Probabilistic methods are gaining in importance in aerospace engineering due to their ability to describe the behavior of the system in the presence of input value variance. A frequently employed probabilistic method is the Monte Carlo Simulation (MCS). There, a sample of random representative realizations is evaluated deterministically and their results are afterwards analyzed with statistical methods. Possible statistical results are mean, standard deviation, quantile values and correlation coefficients. Since the sample is generated randomly, the result of a MCS will differ for each repetition. Therefore, it can be regarded as a random variable. Confidence Intervals (CIs) are commonly used to quantify this variance. To gain the true CI, many repetitions of the MCS have to be conducted, which is not desirable due to limitations in time and computational power. Hence, analytical formulations or bootstrapping is used to estimate the CI. In order to reduce the variance of the result of a MCS, sampling techniques with variance reduction properties like Latin Hypercube Sampling (LHS) are commonly used. But the known methods to determine the CI do not consider this variance reduction and tend to overestimate it instead. Furthermore, it is difficult to predict the change of the CI size with increasing size of the sample. In the present work, new methods to calculate the CI are introduced. They allow a more precise CI estimation when LHS is used for a MCS. For this purpose, the system is approximated by means of a meta model. The distribution of the result value is now approximated by repeating the MCS many times. The time consuming deterministic calculations of a MCS are thus replaced with an evaluation on the meta model. These so called virtual MCS can therefore be performed in a short amount of time. The estimated distribution of the result value can be used to estimate the CI. It is, however, not sufficient to use only the meta model. The error ε, defined as the difference between the true value y and the approximated value y, must be considered as well. The generated meta model can also be used to predict the size of the CI at different sample sizes. The suggested methods were applied to two test cases. The first test case examines a structural mechanics application of a bending beam, which features low computational cost. This allows to show that the predicted sizes of the CI are sufficiently precise. The second test case covers the aerodynamic application. Therefore, an aerodynamic Computational Fluid Dynamics (CFD) analysis accounting for geometrical variations of NASA’s Rotor 37 is conducted. For this, the blade is parametrized with the in-house tool Blade2Parameter. For different sample sizes, blades are generated using this parametrization. Their geometrical variance is based on experience values. CFD calculations for these blades are performed with the commercial software NUMECA. Afterwards, the CIs for result values of interest like mechanical efficiency are evaluated with the presented methods. The suggested methods predict a narrower and thus less conservative CI.