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Micro gas turbine (MGT) is widely used in small-scale distributed power systems because of its low emissions and fuel flexibility. However, the under-utilization of its exhaust heat and the low electric efficiency are the main bottlenecks that restrict its application. Additionally, the flexible switching between the power generated by the MGT and the power grid is also a key factor for keeping the secure operation of a distributed power station. Therefore, this paper conducted some experimental investigations of a 30 kW MGT to provide reference solutions for the above issues. This MGT is located at Shanghai Jiao Tong University (SJTU), which is designed by the Gas Turbine Research Institute of SJTU, and is manufactured by a turbo-machinery factory in Chongqing, China. The demonstration prototype is mainly composed of a single stage centrifugal compressor, a radial turbine, a combustor, a high-speed permanent magnet generator, and a control system. The results show that the MGT can achieve steady operation at a low rotational speed from 10000 r/min to 34000 r/min in the case of using oil lubricated bearings, which can greatly reduce the economic cost compared with the use of air bearings. At the same time, the ignition success rate of combustion chamber (CC) reaches 98% at a low rotational speed, and a wide range of stable combustion area can be obtained, because of the novel design method of combustor by referencing the way applied in an axial flow aero-engine. The MGT generating set can achieve functions, such as starting up, ignition, stable operation, loaded operation, grid-connection and stopping. This system also can realize flexibly switching from the start motor mode to the generator mode, and from grid-connected mode to off-grid mode, because the innovative multi-state switching control system is adopted. The above research work can make our state master independent intellectual property rights of micro gas turbine, rather than continue to be subject to the technological monopoly of the developed states, which can provide theoretical and experimental support for the industrialization of MGT in China.

Radial turbines used in turbochargers and micro-turbines are subjected to high inlet temperature. This creates high thermal stress in the turbines, and possible creep of turbine inducer blades, and can reduce turbines’ reliability. With the ever-stringent engine emission regulations and the continuous drive for engine power density, turbine inlet temperature is significantly increased recently and the risk of thermo-mechanical failure of turbine rotor is heightened. To solve this problem, an innovative turbine cooling method is proposed by injecting a small amount of compressor or intercooler discharge air onto the upper backdisc region of turbine rotor to cool the disc and the inducer blades. A conjugate heat transfer simulation was carried out to investigate the effects of this cooling method with a turbocharger turbine. Flow conditions and geometric configurations were investigated for their influences on the cooling effectiveness of the method. The results show that using the compressor discharger air after intercooler with only 0.5–2.0% of turbine mass flow, the averaged cooling efficiency of the turbine backdisc is promoted by 23–43%; only four to six jets may be needed to cool the entire backdisc; and turbine efficiency is reduced by less than 1% point.

A vented Oscillating-Water-Column (OWC) simplifies the pneumatic energy conversion problem by rectifying air flow and enabling a unidirectional-air-turbine to be employed. It shifts power-extraction to the inhalation phase of the cycle and provides equivalent pneumatic power to a full-wave-cycle. Conventional Radial-air-turbines feature a low global-efficiency in OWC applications, however they offer simpler designs and lower thrust loads. The aim of this study is to modify the design of a centripetal-radial-turbine for optimum efficiency in steady-state using CFD methods for application with the pressure/flow profile experienced by the vented-OWC. Nine design variables were used to control the shape of the rotor and its adjustment to the inward-flow direction. The optimized rotor was found to achieve significant efficiency and output power by using asymmetric and non-zero-staggered blades. The downstream section was optimized for an efficient matching with the optimized-inflow-rotor and four parameters were used to control the shape of the downstream section. A diffuser with a 7-degree diffusion-angle was found to be the optimal connection between the turbine and the chamber. The inflow radial turbine obtained 81% peak efficiency in the steady-state, and its average efficiency over the expected flow coefficients is comparable to the axial-turbines used with OWCs.

[EN] During normal operation, radial turbines may work in off-design conditions. Off-design conditions may be characterised by very low expansion ratios, very high expansion ratios, very low rotational speeds or very high rotational speeds. All of these cases are difficult to characterise experimentally due to high experimental uncertainties or a lack of capabilities in the system feeding pressurised air to the turbine. Also, there are two- and three-dimensional computational fluid dynamics simulations at these operating points but could not be accurate enough due to high turbulence effects, flow detachment and shock wave generation. With a lack of high-quality data, experimental or computational, to fit the reduced-order turbine models used in zero- and one-dimensional engine simulations, there are large uncertainties associated to their results in off-design conditions. This work develops an experimental facility able to characterise the internal flow of radial turbine stators in terms of pressure and velocity fields at off-design and regular working conditions. The facility consists of an upscaled model of a radial turbine volute and stator fed with air in pressure- and temperature-controlled conditions, so different sensors can be used inside it with the least amount of flow disturbance. The different restrictions considered in the design of the upscaled model are presented, and their effects in the final experimental apparatus capabilities are discussed. A preliminary comparison between computational fluid dynamics simulations and experimental data shows encouraging results., The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was partly sponsored by the programme 'Ayuda a Primeros Proyectos de Investigacion (PAID-06-18), Vicerrectorado de Investigacion, Innovacion y Transferencia de la Universitat Politecnica de Valencia (UPV), Spain'. The support given to Ms N.H.G. by Universitat Politecnica de Valencia through the 'FPI-Subprograma 2' (No. FPI-2018-S2-1368) grant within the 'Programa de Apoyo para la Investigacion y Desarrollo (PAID-0118)' is gratefully acknowledged.

For a radial turbine with vaneless volute, the inflow of turbine rotor usually has a circumferential flow distortion due to the influence of the volute tongue. The rotating blades of the rotor are exposed to harmonic aerodynamic loads caused by the distortion, which may induce rotor resonance and lead to high cycle failures (HCF). To understand the forced response mechanism clearly, a numerical analysis was carried out based on a fluid structure interaction (FSI) method. The pressure functions were extracted from the results of a computational fluid dynamics (CFD) analysis by Fourier decomposition. The first three harmonic pressures were identified as the primary engine order (EO) excitations and imposed on the structural model for computational structural dynamics (CSD) simulation. The quantification and assessment of the rotor response were attained by mode superposition method. The simulation results are shown to be consistent with the predictions of Singh’s advanced frequency evaluation (SAFE) diagram.

Organic Rankine cycle an alternative way of generating energy from waste heat, fuel and gases at low-temperature. Method (ORC) proved successful and high efficiency to reduce environmental pollution, fuel consumption and convert low to medium heat sources. The paper will be presenting a review investigation on the organic Rankine cycle(ORC), cycle Background, (ORC) configuration, and selecting of working fluids and experimental studied of expansion apparatuses, which are classified into two type volumetric type such as (expander of rotary vane, scroll, reciprocating piston expander and screw) velocity kind (for example axial and radial turbine). Heat exchanger and expander apparatuses are considered economically expensive parts in (ORC).

The time taken for CAD modelling a single component and then building the family of that component consumes a lot of time and is a rigorous task. This problem can be solved by applying parametrisation to the component and make it adapt to changes in the design inputs. The Thermodynamically valid model is based on set of numerical relations. This type of approach requires real experimental data to be legitimate. This method of applying experimental data and back-end usage of thermodynamics equations allows us to create a valid model for industrial usage. This is the objective behind designing of turbocharger turbine parametric modeller. The modeller not only gives direct control of the blade geometry but also provides valuable feedback of the design. This has allowed the user to construct a good initial design before refining it with more computationally expensive methods. The modeller is developed using the python API within the framework of the open source software FreeCAD. The approach to construct a variety of turbo machinery turbines is based partially on state-of-art parametrisation techniques and uses fundamental design variables such as Specific speed, Flow Coefficient and Fluid inlet conditions. The modeller is based on experimental results of turbocharger turbines as well as thermodynamics study of Radial turbines. The outcome of designing the modeller helped in minimizing the time of manual modelling with an automated process

[ES] Se desarrollan en este trabajo el proceso de testeo y modelado de un turbogrupo de automoción para su uso en un ciclo Brayton inverso de refrigeración, su implementación en el ciclo junto a una campaña experimental con su posterior análisis y el desarrollo de un modelo validado con los resultados obtenidos. El ciclo se compone de intercambiadores de calor aire-agua provenientes de la industria automotriz, así como compresores eléctricos del tipo supercharger para proporcionar potencia al fluido de trabajo. Se trata de un ciclo que se ha probado capaz de alcanzar temperaturas de hasta 115K utilizando aire como fluido de trabajo únicamente con aporte eléctrico, lo que supone una ventaja frente a legislaciones sobre fluidos típicos usados en refrigeración. Se evalúan los aspectos que aportan valor a la propuesta y el análisis de resultados gracias a la elevada sensorización de la instalación, así como al desarrollo del gemelo digital proporcionan información sobre aspectos clave para mejorar la eficiencia del sistema., [EN] In this work, three primary purposes are developed: the testing and modeling process of an automotive turbocharger for its use in an inverse Brayton refrigeration cycle. Secondly, the implementation of the turbocharger in the cycle doing an experimental campaign with its subsequent analysis. Finally, a model is developed and validated with the obtained results. The cycle is made up of air-water heat exchangers from the automotive industry, as well as supercharger-type electric compressors to provide power to the working fluid. This cycle has reached temperatures up to 115K using air as the working fluid only with an electrical input, which is an advantage over legislation on typical fluids used in refrigeration. The aspects that add value to the proposal are evaluated. The analysis of results, thanks to the high sensorization of the installation and the development of the digital twin, provides information on critical aspects to improve the efficiency of the system.

Turbine as a key power unit is vital to the novel supercritical carbon dioxide cycle (sCO2-BC). At the same time, the turbine design and optimization process for the sCO2-BC is complicated, and its relevant investigations are still absent in the literature due to the behavior of supercritical fluid in the vicinity of the critical point. In this regard, the current study entails a multifaceted approach for designing and optimizing a radial turbine system for an 8 MW sCO2 power cycle. Initially, a base design of the turbine is calculated utilizing an in-house radial turbine design and analysis code (RTDC), where sharp variations in the properties of CO2 are implemented by coupling the code with NIST’s Refprop. Later, 600 variants of the base geometry of the turbine are constructed by changing the selected turbine design geometric parameters, i.e., shroud ratio (rs4r3), hub ratio (rs4r3), speed ratio (νs) and inlet flow angle (α3) and are investigated numerically through 3D-RANS simulations. The generated CFD data is then used to train a deep neural network (DNN). Finally, the trained DNN model is employed as a fitting function in the multi-objective genetic algorithm (MOGA) to explore the optimized design parameters for the turbine’s rotor geometry. Moreover, the off-design performance of the optimized turbine geometry is computed and reported in the current study. Results suggest that the employed multifaceted approach reduces computational time and resources significantly and is required to completely understand the effects of various turbine design parameters on its performance and sizing. It is found that sCO2-turbine performance parameters are most sensitive to the design parameter speed ratio (νs), followed by inlet flow angle (α3), and are least receptive to shroud ratio (rs4r3). The proposed turbine design methodology based on the machine learning algorithm is effective and substantially reduces the computational cost of the design and optimization phase and can be beneficial to achieve realistic and efficient design to the turbine for sCO2-BC.

The pulsating flow conditions which a turbocharger turbine is exposed cause important deviations of the turbine aerodynamic performance when compared to steady flow conditions. Indeed, the secondary flows developing in the turbine are determined by the inflow aerodynamic conditions, which largely vary during the pulse cycle. In this paper, a high-resolved Large Eddy Simulation is performed to investigate and characterize the flow field evolution in a turbocharger radial turbine over the pulse cycle. At first, the model is validated against experimental results obtained in gas-stand flow conditions. Then, the instantaneous flow field at the rotor mid-span section is compared to the one given by the equivalent cycle-averaged steady flow conditions. The results highlight five distinct flow features. At low mass flow rates, when the relative inflow angle assumes large negative values, the flow separates at the blade pressure side, causing a secondary flow consisting in two counter-rotating vortices characterized by a diameter comparable to the blade passage. As the mass flow rate increases, the first vortex persists at the blade tip while the second one moves closer to the blade trailing edge. This corresponds to the second characteristic flow field. With increasing relative inflow angle, for the third characteristic flow feature, only the recirculation at the blade leading edge is displayed and its size gradually reduces. For the fourth characteristic flow feature, at moderate negative values of the relative inflow angle, the flow field is well aligned with the blade profile and free of secondary flows. Then, as the relative inflow angle gradually grows towards large positive values, the flow separates on the blade suction side causing the mixing of the flow with the stream flowing on the pressure side of the previous blade.

Para o cultivo de banana utilizam-se alguns agentes químicos para combater determinadas pragas, uma destas é a Sigatoka, causada pelo fungo Mycosphaerella Musicola. Ela ataca as folhas das bananeiras, diminuindo drasticamente a produtividade da fruta. Para eliminação desta praga, realiza-se pulverizações de agentes químicos, a quantidade destas variam de acordo com diversos fatores. Para realizar a pulverização utiliza-se o atomizador de ar, tipo canhão bananeiro, objeto de estudo deste trabalho. Este atomizador possui uma turbina radial, que impulsiona ar para um direcionador giratório de 4 a 6m de altura, para fazer o lançamento dos agentes químicos necessários no bananal. Existem diferentes combinações disponíveis de turbinas e ventiladores para este equipamento e o objetivo deste trabalho é avaliar através de análises computacionais combinatórias, as diferentes combinações indicando o melhor conjunto, para aprimorar a trajetória e temperatura de saída do fluído melhorando a eficiência da pulverização, aumentando a produtividade com menor número de pulverizações e consequentemente reduzindo o impacto ao meio ambiente. O trabalho foi desenvolvido através de uma pesquisa exploratória em campo, também conhecida como “pesquisa de base”. Nos resultados pode-se observar que dentre as condições analisadas de trajetória, temperatura e pressão, que o melhor conjunto de turbina e ventilador, que oferece os melhores resultados é a turbina com saída de ar central e ventilador de pás retas, com diferença de temperatura de 1,7°C menor, para as temperaturas coletadas em campo e 0,36°C menor, para as temperaturas das análises computacionais.

Against the background of a growing deployment of renewable electricity production, like wind and solar, the demand for energy storage will only increase. One of the most promising ways to cover the medium to long-term storage is to use the excess electricity to produce hydrogen via electrolysis. In a modern energy grid, filled with intermittent power sources and ever-increasing problems to construct large power plants in densely populated areas, a network of Decentralised Energy Systems (DES) seems more logical. Therefore, the importance of research into the design of a small to medium-sized hydrogen fuelled micro Gas Turbine (mGT) unit for efficient, local heat and electricity production becomes apparent. To be able to compete with Reciprocating Internal Combustion Engines (RICEs), the mGT needs to reach 40% electrical efficiency. To do so, there are two main challenges; the design of an ultra-low NOX hydrogen combustor and a high Turbine Inlet Temperature (TIT) radial turbine. In this paper, we report on the progress of our work towards that goal. First, an improvement of the initial single-nozzle swirler (swozzle) combustor geometry was abandoned in favour of a full CFD (steady RANS) design and optimisation of a micromix type combustion chamber, due to its advantages towards NOx-emission reduction. Second, a full CFD design and optimisation of the compressor and turbine is performed. The improved micromix combustor geometry resulted in a NOx level reduction of more than 1 order of magnitude compared to our previous swozzle design (from 1400 ppm to 250 ppm). Moreover, several design parameters, such as the position and diameter of the hydrogen injection nozzle and the Air Guiding Panel (AGP) height, have been optimized to improve the flow patterns. Next to the combustion chamber, CFD simulations of the compressor and turbine matched the 1D performance calculations and reached the desired performance goals. A CFD analysis of the impact of the tip gap and exhaust diffuser cone angle led to a choice of these parameters that improved the compressor and turbine performance with a limited loss in efficiency.

A novel control technique for radial turbines is under investigation for providing turbine performance controllability, especially in turbocharger applications. This technique is based on replacing the traditional spiral casing with a Multi-channel Casing (MC). The MC divides the turbine rotor inlet circumferentially into a certain number of channels. Opening and closing these channels controls the inlet area and, consequently, the turbine performance. The MC can be distinguished from other available control techniques in that it contains no movable parts or complicated control mechanisms. Within the casing, this difference makes it practical for a broader range of applications. In this investigation, a turbocharger featuring a turbine with MC has been tested on a hot gas test stand. The experimental test results show a reduction in the turbine operating efficiency when switching from full to partial admission. This reduction increases when reducing the admission percentage. To ensure the best performance of the turbine featuring MC while operating at different admission configurations, it becomes crucial to investigate its internal flow field at both full and partial admission to understand the reasons for this performance reduction. A full 3D Computational Fluid Dynamics (CFD) model of the turbine was created for this investigation. It focuses on identifying the loss mechanisms associated with partial admission. Steady and unsteady simulations were performed and validated with available test data. The simulation results show that operating the turbine at partial admission results in highly disturbed flow. It also detects the places where aerodynamic losses occur and which are responsible for this performance reduction. This operation also shows flow unsteadiness even when operating at steady conditions. This unsteadiness depends mainly on the admission configuration and percentage.

Radial inflow turbine and nozzle among the other components of the cryogenic turboexpander has a significant effect on the efficiency of the system. This study proposes an effective one-dimensional design approach of a radial turbine by introducing different loss correlations. The methodology also describes the effect of non-dimensional design variables on the performance of the turbine. These variables (blade speed ratio, pressure ratio, hub and shroud to turbine inlet radius ratio) undergo artificial intelligence-based model to predict their optimal range for better efficiency and power output of the turbine. Based on these optimal ranges, two turbine and nozzle models are generated. The results of the optimized configuration show that the turbine total-to-static efficiency and power output are higher by 4% and 18.9% respectively as compared to the existing literature. Thereafter, the three-dimensional computational fluid dynamics (CFD) analysis is carried out to visualize the fluid flow and thermal characteristics at different inlet temperatures in the flow passage using ANSYS CFX®. The study also focuses to identify the flow separation zone, tip leakage flow, vortex formation, secondary losses and its reasons at different spans of the turbine. An experimental platform is also established to validate the CFD results of a case study. The experimental results show that the mass flow rate and rotational speed has major effect on temperature drop and isentropic efficiency of the turboexpander. The study highlights the importance of the design methodology, the estimation capability of artificial intelligence models, the experimental techniques and benchmarking model for numerical analysis at different cryogenic temperature.

Solid oxide fuel cell (SOFC) vehicles are considered to have broad prospects for development, and the high operating temperature of SOFC results in great potential for waste-heat recovery. Many concepts for utilizing waste heat of SOFC have been suggested and studied, and most of them directly couple an SOFC to a gas turbine, which require the SOFC to operate at an elevated pressure and make the system less flexible and thus harder to operate. In recent years, with the development of turbine and heat exchanger technology, the supercritical carbon dioxide (S-CO2) power cycle has raised widespread attractions for the waste recovery. This study explores the potential of S-CO2 Brayton cycle to realize waste-heat recovery for an SOFC vehicle. The SOFC can operate at atmospheric pressure, and the hybrid system is easier to operate than the directly coupled systems. In this paper, a simple recuperated S-CO2 Brayton cycle is proposed and the key component, radial inflow turbine is designed and focused. The flow state of the designed turbine is analyzed in detail based on computational fluid dynamics (CFD) numerical simulation. Five cases with different impeller tip clearances are numerically simulated to study its influence on the turbine performance. In addition, off-design performance analysis of the radial inflow turbine is conducted considering the temperature fluctuation of SOFC in practical applications.

The thermal condition of a turbocharger considerably differs between different applications, which makes it difficult to model the heat transfer. In this study, a general procedure to characterize the heat transfer model for a radial turbine was established using 3D Conjugate Heat Transfer (CHT) simulation. The external convective and radiation heat losses were modelled by an equivalent convection heat transfer coefficient and an equivalent metal emissivity, following an analysis of the heat transfer mechanisms. The established model was validated by measurements under adiabatic and diabatic conditions. The characterization procedure was further simplified to extend its applications. The number of required operating points for simulation and measurements were significantly reduced, which enabled it to be used under different operating conditions, e.g., engine test and in-vehicle operations, where a constant turbo speed line could hardly be regulated. Then a comparison was conducted with a reference model based on the geometric simplification. The proposed model was observed to give a slightly better result regarding turbine housing temperatures under low and high turbine inlet temperatures. In the end, an analysis of turbine heat flow was conducted, which indicated that on average 80.4% of the turbine internal heat transfer occurred at the volute and 17.3% at the diffuser. Besides, the external heat losses can be up to 2.511 times of the turbine mechanical power.

In present study, the effect of back cavity in a radial inflow turbine is investigated numerically. The size effect of labyrinth seal clearance is revealed. The performances of radial turbine with back cavity at different total expansion ratio are also investigated. Results illustrate that the clearance variation of original labyrinth seal in back cavity has limited effect on the leakage flow and the isentropic efficiency. The existence of back cavity reduces the isentropic efficiency at every total expansion ratio, and a maximum isentropic efficiency reduction of 1.5% is obtained when total expansion ratio is 2.89. To control the rotor‐back cavity coupling flow loss, a “rotor‐back cavity seal” is also proposed, and the isentropic efficiency of radial turbine is significantly improved at different total expansion ratio.

In this study, the effects of the scroll passage shape and the nozzle vane on the flow behavior at the inlet of turbine impeller of turbocharger with VGS were investigated experimentally at the middle and the high flow rate conditions by using 5-hole Pitot tube. The oil flow visualizations were also conducted on the solid walls inside the nozzle to examine the flow behavior in detail and to verify the data obtained by 5-hole Pitot tube. The experimental results clarified that the effects of the overhang shape of scroll and the existence of the nozzle vane especially on the circumferential uniformity of the flow field at the outlet of the nozzle region depended on the flow rate.

The optimization of OWC devices has deserved much attention in the last few years. However, despite of this intense research activity, the most suitable turbine for OWC applications is still under debate. Recently, the twin-turbine configuration, where two unidirectional turbines are employed simultaneously, has emerged as a promising design. Although axial turbines are typically employed for those systems, the present paper demonstrates that the use of radial turbines can be also an interesting option. In this work a radial geometry, specifically designed to be used in a twin-turbine configuration, has been manufactured at a reasonable cost for a lab-scale facility taking advantage of 3D printing technology. Encouraging preliminary results were obtained in an aerodynamic database of the turbine. In particular, the total-to-static efficiency under stationary conditions (i.e. at constant flow coefficients) reached remarkable high values. Hence, the performance curve of the turbine under such stationary conditions has been used to make an assessment of its non-stationary performance in order to compare this optimized radial turbine with respect to impulse axial types available in the literature. The results revealed that radial turbines are clearly competitive against to axial ones when introduced in a twin-turbine configuration for OWC power plants.

The article deals with the numerical simulation of unsteady flows through the turbine part of the turbocharger. The main focus of the article is the extension of the in-house CFD finite volume solver for the case of unsteady flows in radial turbines and the coupling to an external zero-dimensional model of the inlet and outlet parts. In the second part, brief description of a simplified one-dimensional model of the turbine is given. The final part presents a comparison of the results of numerical simulations using both the 3D CFD method and the 1D simplified model with the experimental data. The comparison shows that the properly calibrated 1D model gives accurate predictions of mass flow rate and turbine performance at much less computational time than the full 3D CFD method. On the other hand, the more expensive 3D CFD method does not need any specific calibration and allows detailed inspections of the flow fields.

The organic Rankine cycle makes it possible to accomplish energy recovery from a low-temperature heat source, which is typically not recovered for economic reasons. As the expander for the organic Rankine cycle, the radial turbine is easy to manufacture and has advantages in terms of size and efficiency. The radial turbine design modeler (RTDM), which was developed from in-house code, is a preliminary design program for radial inflow turbines and is different from the commercially available program RITAL. In this study, an experiment on radial inflow turbines is performed using both RTDM and RITAL. As a result, the output and efficiency of the RTDM and RITAL turbines are 36.04 kW, 80.03% and 35.03 kW, 76.01%, respectively. Experimental results demonstrate that the performance of the RTDM turbine is almost similar to the RITAL turbine. We also perform analysis on performance prediction utilizing a deep neural network with two hidden layers based on the experimental data. As a result, the minimum root mean squared errors of the RTDM turbine and RITAL turbine are estimated to be approximately 1.81 and 1.65, respectively. The deep neural network is able to predict the trends of the experiment for the organic Rankine cycle.

To maximize the exergy utilization efficiency of a Kalina cycle system with an ammonia-water radial turbine at off-design conditions, this study proposes a novel control approach named optimal control approach. An off-design model for ammonia-water radial-inflow turbine using variable nozzles is constructed. The optimal control approach is realized by changing the outlet angle of the radial-inflow turbine nozzle and the turbine inlet pressure. Design parameters of heat source (waste hot water) are 130 °C and 10 kg/s. To find out the performance advantage for the novel control approach, it is compared with two traditional control approaches. The results show that the proposed novel control approach presents the highest exergy utilization efficiency and net power at off-design conditions. The net power ratio of the optimal control approach to the traditional sliding pressure control approach reaches 111.22% as the heat source mass flow rate declines to 5 kg/s. Compared with the traditional approach for constant pressure control (changing turbine nozzle outlet angle), the optimal control approach has a potential to produce 3.11% more net power. The exergy utilization efficiency is generally declined with the elevated heat source mass flow rate at the approach for optimal control, while the system thermal efficiency is slowly increased.

The oscillating-water-column (OWC) is a ubiquitous style of wave-energy-converter for harnessing significant power from ocean waves. A new configuration of OWC described here as a vented-OWC provides opportunity to simplify air-turbine design by limiting the power extraction to inhalation mode. The asymmetric airflow profile of the vented-OWC requires a unidirectional-turbine configuration to be adopted. The focus of this study is to analyse a unidirectional radial air-inflow-turbine design using Computational-Fluid-Dynamics (CFD) suitable for application with a vented-OWC. It is found that downstream of the rotor can cause significant energy losses due to its narrow flow passage. Two configurations of an inward-flow radial turbine were also compared, the first by keeping the casing height constant throughout the turbine domain and the second by increasing the casing height in a way to keep a constant sectional area from inlet to the outlet of the turbine domain. The latter configuration obtained a ten percent gain in peak efficiency compared to the first. The difference is identified as fewer energy losses at the downstream section and comparably higher torque for the same flow-coefficient. Introduction of downstream-guide-vanes was found to retard the chocking phenomenon, which offers a wider operational range for the radial-inflow design.

The paper presents a comprehensive numerical and experimental analysis of the Tesla turbine. The turbine rotor had 5 discs with 160 mm in diameter and inter-disc gap equal to 0.75 mm. The nozzle apparatus consisted of 4 diverging nozzles with 2.85 mm in height of minimal cross-section. The investigations were carried out on air in subsonic flow regime for three pressure ratios: 1.4, 1.6 and 1.88. Maximal generated power was equal to 126 W and all power characteristics were in good agreement with numerical calculations. For each pressure ratio, maximal efficiency was approximately the same in the experiment, although numerical methods proved that efficiency slightly dropped with the increase of pressure ratio. Measurements included pressure distribution in the plenum chamber and tip clearance and temperature drop between the turbine’s inlet and the outlet. For each pressure ratio, the lowest value of the total temperature marked the highest efficiency of the turbine, although the lowest static temperature was shifted towards higher rotational speeds. The turbine efficiency could surpass 20% assuming the elimination of the impact of the lateral gaps between the discs and the casing. The presented data can be used as a benchmark for the validation of analytical and numerical models.

The radial turbine impeller of an exhaust turbocharger is analyzed in view of both free vibration and forced response. Stator vane rings located upstream between engine and turbine wheel are applied to guide the exhaust gases in optimized flow directions. Hence, turbine wheels are subjected to aerodynamic excitations causing forced vibrations of blades and the whole turbine. Due to random blade mistuning resulting from unavoidable inaccuracies in manufacture or material inhomogeneities, localized modes of vibration may arise, which involve the risk of severely magnified blade displacements and inadmissibly high stress levels compared to the tuned counterpart. In consequence, damages may occur along with a dramatic decrease of efficiency or even a total failure during engine operation as worst-case scenarios. Contrary, the use of intentional mistuning has proved to be an efficient measure to mitigate the forced response. Independently, the presence of aerodynamic damping is significant with respect to limit the forced response since structural damping ratios of blade integrated disks (blisks) typically take extremely low values. Thus, a detailed knowledge of respective damping ratios would be desirable while developing a robust blisk design. For this, far-reaching experimental investigations are carried out to determine damping curves of a comparative wheel within a wide pressure range by simulating operation conditions in a pressure tank. They are the basis to develop empirical formulas for damping estimation which could be be taken into account during future design processes. In order to get an idea of the real structural behaviour, further measurements are conducted to determine the present mistuning of the turbine wheel, which facilitates to update structural models and finally allows to compute the forced response in an accurate manner. Reduced order models are built up for designing suitable intentional mistuning patterns by using the subset of nominal system mode (SNM) approach introduced by Yang and Griffin [1], which conveniently allows for accounting both differing mistuning patterns and the impact of aeroelastic interaction. For this, the aerodynamic damping curves are determined by means of computational flow simulations. The SNM approach finally provides appropriate mistuning patterns by conducting optimization studies based on genetic algorithms. The robustness of the found solutions is proved by additionally superimposing both random mistuning and experimentally determined mistuning of the original wheel. Finite element analyses are carried out in order to identify appropriate measures to implement intentional mistuning patterns, which are featuring only two different blade designs. In detail, the impact of specific geometric modifications on blade natural frequencies is investigated. After implementation of the intentional mistuning pattern, which will be described in Part 2 of this paper later on, the success of taken measures will be reviewed based on both, experimental testing at standstill conditions and in a test stand by running the wheel under realistic operational conditions. [1] Yang, M. T., Griffin, J. H., „A Reduced-Order model of Mistuning Using a Subset of Nominal System Modes“. J Eng Gas Turb Power, 123, pp. 893-900 (2001).

Radial impellers are not internally-cooled because of the manufacturing challenge. The conventional manufacturing method for internally-cooled components is an investment cast process using a ceramic core to create internal passages. This approach has been developed for axial gas turbines for the past few decades and is a low-risk manufacturing approach for single blade castings. However, conventional manufacturing methods are difficult to apply to a radial impeller in a cost-effective manner. For example, the entire impeller (blades and the hub) are typically manufactured from a single piece of material. Therefore, if one blade is poorly cast, the entire impeller must be thrown away. To overcome the complexity and reduce production risk, additive manufacturing can be used to build internally-cooled radial impellers. Additive manufacturing is a growing area and gaining operational experience is required to confidently build complex parts, such as a radial impeller with small, internal passages. In this paper, additive manufacturing is used to avoid the challenges of conventionally manufacturing. Multiple iterations of the internal cooling design are examined to illustrate lessons learned. Flow and heat transfer tests are used to verify the impeller cooling design. Material properties are discussed to verify that the impeller can withstand high rotational stresses.

An aerodynamic design optimization study of the nozzle vane of a variable geometry turbine (VGT) turbocharger for a diesel engine application was conducted using the commercial software, ANSYS CFX and DesignXplorer. The nozzle design was optimized at three critical engine operating points. The nozzle shape was parameterized using key design parameters including theta angle, thickness value and opening angle. For a good balance of computational time and accuracy, the optimization approach adopted meta-models and response surfaces to represent the training data and reduce the number of simulations required to reach an optimal design. Finally, more than 300 optimized designs were simulated to assess the performance and characteristics of each design. The final optimized nozzle design met all the design constraints and showed an improvement of up to 2% efficiency and reduced the maximum torque by 20% compared to the baseline nozzle.

Recent advancements in internal combustion engine for efficient fuel combustion, such as application of miller cycle, where the closing of engine intake valve is purposely delayed to provide more cooling of air-fuel mixture during compression stroke for better engine efficiency, has led to a requirement for turbochargers to function at a wider operating range and higher compression ratio. One of the methods which have been largely accepted is the use of variable geometry turbochargers. As compared to diesel engine, operating conditions for gasoline engine require the turbine to operate at higher exhaust temperature, which increases the risk of damaging the rotor. This paper discusses a detailed flow analysis of the effect of tip leakage and nozzle vane wake flow on surface pressure distribution of the turbine rotor, especially at the severe condition when vane trailing edge and rotor leading edge are in proximity. It was observed in steady and unsteady CFD simulations that the origination and propagation of tip leakage flow can be varied depending on the blade loading at the rotor leading edge, and the major interaction of nozzle wake can be switched from pressure surface to suction surface as rotor blade crossed a nozzle vane, which can drastically affect the alternating aerodynamic stresses. The sensitivity to this phenomenon has been evaluated by calculating the safety factor. The authors modified the rotor design to weaken the effect of tip leakage flow in order to suppress variations in rotor surface pressure as it crosses the nozzle vane. It significantly reduced the alternating stress and increased the safety factor at vibration mode 2 from 0.3 to 9.3 and mode 3 from 0.6 to 3.2 respectively.

In recent years, the automotive sector has been focused on emission reductions using hybrid and electric vehicles. This was mainly caused by political trends promoting “green energy”. However, that does not mean that internal combustion engines (ICEs) should be forgotten. The ICE has still the potential of recovering energy from exhaust gases. One of the promising ways to recover energy is turbocharging. Over the years engine manufacturers have designed very efficient turbocharger systems which have greatly increased the overall engine efficiency. This led to pollutant emission reductions. This paper presents the results of the three-dimensional (3-D) numerical simulations of the two-stage, six-inlet turbocharging system under the influence of unsteady, pulsed-flow conditions. The calculations were carried out for three turbine speeds. The most interesting results of this study were the separation of exhaust gases coming from the six-exhaust pipes and the performance of both stages under pulse-flow conditions. The two-stage turbocharging system was compared against the single-stage turbocharging system and the results showed that the newly designed two-stage turbine system properly separated the exhaust gases of the adjacent exhaust pipes.