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The deposition of combustion residues in the nozzle ring (NR) of a turbocharger turbine stage changes the NR geometry significantly in a random manner. The resultant complex and highly asymmetric geometry induces low engine order (LEO) excitation, which may lead to resonance excitation of rotor blades and high cycle fatigue (HCF) failure. Therefore, a suitable prediction workflow is of great importance for the design and validation phases. The prediction of LEO excitation is, however, computationally expensive as high-fidelity, full annulus CFD models are required. Previous investigations showed that a steady-state computational model consisting of the volute, the NR, and a radial extension is suitable to reduce the computational costs massively and to qualitatively predict the level of LEO forced response. In the current paper, the aerodynamic excitation of 69 real contaminated NRs is analyzed using this simplified approach. The results obtained by the simplified simulation model are used to select 13 contaminated NR geometries, which are then simulated with a model of the entire turbine stage, including the rotor, in a transient time-marching manner to provide high-fidelity simulation results for the verification of the simplified approach. Furthermore, two contamination patterns are analyzed in a more detailed manner regarding their aerodynamic excitation. It is found that the simplified model can be used to identify and classify contamination patterns that lead to high blade vibration amplitudes. In cases where transient effects occurring in the rotor alter the harmonic pressure field significantly, the ability of the simplified approach to predict the LEO excitation is not sufficient. [ABSTRACT FROM AUTHOR]

In the present study, a 100 kW organic Rankine cycle is suggested to recover heat energy from commercial ships. A radial-type turbine is employed with R1233zd(E) and back-to-back layout. To improve the performance of an organic Rankine power system, the efficiency of the turbine is significant. With the conventional approach, the optimization of a turbine requires a considerable amount of time and involves substantial costs. By combining design of experiments, an artificial neural network, and Latin hypercube sampling, it becomes possible to reduce costs and achieve rapid optimization. A radial basis neural network with machine learning technique, known for its advantages of being fast and easily applicable, has been implemented. Using such an approach, an increase in efficiency greater than 1% was achieved with minimal design changes at the first and second turbines. [ABSTRACT FROM AUTHOR]

In this paper, a 100 kW radial inflow turbine is designed for an ocean thermal energy conversion (OTEC) power plant based on the organic Rankine cycle (ORC) with ammonia as the working fluid. Based on one-dimensional (1D) and three-dimensional computational fluid dynamics (3D-CFD) modeling, the mechanical structure design, static and modal analyses of the turbine and its components are carried out to investigate its mechanical performance. The results show the stress and strain distribution in the volute, stator and rotor, and their maximum values appear, respectively, at the inlet cutout, the tip of the stator outlet and the connection position between the rotor and the shaft. After optimization, all the stresses in the above components are below the allowable values. The frequencies from the first order to the sixth order of the rotor and whole turbine were obtained through modal analysis without prestress and under prestress. The maximum frequency of the rotor and whole turbine is 707.75 Hz and 40.22 Hz, both of which are far away from the resonance frequency range that can avoid resonance. Therefore, the structure of the designed turbine is safe, feasible and reliable so as to better guide actual production. [ABSTRACT FROM AUTHOR]

The deposition of combustion residues in the nozzle ring (NR) of a turbocharger turbine stage changes the NR geometry significantly in a random manner. The resultant complex and highly asymmetric geometry induces low engine order (LEO) excitation, which may lead to resonance excitation of rotor blades and high cycle fatigue (HCF) failure. Therefore, a suitable prediction workflow is of great importance for the design and validation phases. The prediction of LEO excitation is, however, computationally expensive as high-fidelity, full annulus CFD models are required. Previous investigations showed that a steady-state computational model consisting of the volute, the NR, and a radial extension is suitable to reduce the computational costs massively and to qualitatively predict the level of LEO forced response. In the current paper, the aerodynamic excitation of 69 real contaminated NRs is analyzed using this simplified approach. The results obtained by the simplified simulation model are used to select 13 contaminated NR geometries, which are then simulated with a model of the entire turbine stage, including the rotor, in a transient time-marching manner to provide high-fidelity simulation results for the verification of the simplified approach. Furthermore, two contamination patterns are analyzed in a more detailed manner regarding their aerodynamic excitation. It is found that the simplified model can be used to identify and classify contamination patterns that lead to high blade vibration amplitudes. In cases where transient effects occurring in the rotor alter the harmonic pressure field significantly, the ability of the simplified approach to predict the LEO excitation is not sufficient.

The proper design of a Concentrated solar power (CSP) plant and the associated thermal energy storage requires a careful analysis of the yearly expected irradiance and environmental conditions. System simulations based on accurate components models allow the prediction of the performance of the plant and the analysis of the components interactions. The simulations of various scenarios provide information that will help tuning the design of the components to improve the performance of the whole system at design and off-design conditions. In this paper, the focus is set on the radial turbine expander which is one of the most important component. Classical system simulation approaches use map based performance model for the turbine. This require to generate the performance map either with meanline models, CFD simulations or experiments. This is not very convenient when iterating on the system design and if the actual turbine does not exist yet. In this work, a meanline model for radial inflow turbine operating with real gas has been implemented in MODELICA language for the first time to the authors’ best knowledge. This turbine model has been coupled with the available CSP sCO2 Brayton cycle model in MODELON ThermalPower library. A parametric study on a virtual test bench show the turbine performances for various rotational speed and inlet guide vane angle. The study focus then on the performance prediction of on and off design of the system with a 8 MW turbine obtained with a simple preliminary design calculation. The investigations showed that for the varying load conditions in the solar plant system, an improved operating point has been identified by adjusting the rotational speed and the inlet guide vane angle. Future work will focus on the use such system model with multi objective meta heuristic optimization.

Organic Rankine cycle (ORC) is an effective technology to harness low-grade energy. Turbine, as a key component of ORC, takes advantages of its high efficiency and compact size compared with other expanders. Currently, developing suitable turbines with a high performance and a low cost is one of the bottlenecks for wide applications of various ORCs. In this context, technical progress on radial inflow turbines (RITs), axial turbines (ATs), and radial outflow turbines (ROTs) is introduced, and loss models used in the preliminary design are compared, especially for small-scale ORCs. RIT is recommended for medium and small ORCs with an expansion pressure ratio of <10. The power outs and rotational speeds of the designed RITs spanned the ranges of 9.3–684 kW and 3000–114,000 r/min with an efficiency of 56.1–91.75%. In comparison, the power outputs and speeds of ATs were 3–2446 kW and 3000–91,800 r/min with an efficiency of 63–89.1%. AT is suitable for large-scale ORCs with a power output of greater than hundreds of kW. However, AT with impulse stages is feasible for small-scale ORCs when the pressure ratio is high, and the mass flow rate is small. The power outputs of the designed ROTs were relatively small, at 10–400 kW with a speed of 7200–42,700 r/min and an efficiency of 68.7–85%. For organic working fluids with a large expansion pressure ratio, ROT might be employed. Conventional mean-line models may neglect the effects of supersonic flow, which will be encountered in many ORC turbines. Therefore, adequate models for supersonic expansion loss and shock loss need to be added. Meanwhile, a proper multivariable optimization algorithm such as a gradient-based or stochastic search method should be selected. Finally, the challenges and potential research directions are discussed. The outcomes can provide some insights for the development of ORC turbines and the optimization of ORC systems. [ABSTRACT FROM AUTHOR]

The organic Rankine cycle (ORC) is an efficient technology for electricity generation from low- and medium-temperature heat sources. In this type of power cycle, the radial inflow turbine is the option usually selected for electricity generation. As a critical ORC component, turbine performance markedly affects the efficiency of the system. Therefore, the challenge is to model the behavior of the radial inflow turbine operating with organic fluids for heat recovery applications. In this context, various groups of fluids are highlighted in the scientific literature, including R-123, R-245fa, and R-141b, which are the fluids used in this research. Since little research has focused on the turbine efficiency effect on the power cycle design and analysis, this study presents an analysis of a radial inflow turbine based on a mathematical model of a one-dimensional design of the turbine. From this analysis, geometric, thermal, and operating parameters were determined, as well as volute, stator, and rotor losses. For this purpose, an algorithm was implemented in MATLAB to calculate the one-dimensional parameters of the turbine. Using these parameters, a 3D model of the turbine was designed in ANSYS-CFX, with performance curves of each projected turbine under design and off-design conditions. The numerical results suggest that the isentropic efficiency of all the proposed turbines under design conditions can surpass 75%. Additionally, the findings indicate that different design conditions, such as specific speed, pressure ratio, and turbine size, can affect the efficiency of radial inflow turbines in ORC systems. [ABSTRACT FROM AUTHOR]

The efficiency of hybrid electric vehicles may be substantially increased if the energy of exhaust gases, which do not complete the expansion inside the cylinder of the internal combustion engine, is efficiently recovered using a properly designed turbo-generator and employed for vehicle propulsion. Previous studies, carried out by the same authors of this work, showed a potential hybrid vehicle fuel efficiency increment up to 15% employing a 20 kW turbine on a 100 HP-rated power thermal unit. The innovative thermal unit proposed here is composed of a supercharged engine endowed with a properly designed turbo-generator, which comprises two fundamental elements: an exhaust gas turbine expressly designed and optimized for the application, and a suitable electric generator necessary to convert the recovered energy into electric energy, which can be stored in the on-board energy storage system of the vehicle. In this two-part work, the realistic efficiency of the innovative thermal unit for hybrid vehicles is evaluated and compared to a traditional turbocharged engine. In Part 1, the authors presented a model for the prediction of the efficiency of a dedicated radial turbine, based on a simple but effective mean-line approach; the same paper also reports a design algorithm, which, thanks to some assumptions and approximations, allows fast determination of the right turbine geometry for a given design operating condition. It is worth pointing out that, being optimized for quasi-steady power production, the exhaust gas turbine here considered is quite different from the ones commonly employed for turbocharging applications; for this reason, and in consideration of the required power size, such a turbine is not available on the market, nor has its development been previously carried out in the scientific literature. In this paper, Part 2, a radial turbine geometry is defined for the thermal unit previously calculated, employing the design algorithm described in Part 1; the realistic energetic advantages that could be achieved by the implementation of the turbo-generator on a hybrid propulsion system are evaluated through the performance prediction model under different operating conditions of the thermal unit. As an overall result, it was estimated that, compared to a reference traditional turbocharged engine, the turbo-compound system could gain vehicle efficiency improvement between 3.1% and 17.9%, according to the output power delivered, with an average efficiency increment of 10.9% evaluated on the whole operating range. [ABSTRACT FROM AUTHOR]

Internal combustion engine (ICE) exhaust gases provide a high amount of energy which is partially lost to the environment. Such energy can be recovered with a turbocharger turbine or other after-treatment device. As the engine exhaust flow varies not only with the engine load but also with the opening and closing of the exhaust valves, a proper matching between the engine and the turbine should be established to maximize the recovery of waste energy. That is why a twin-scroll or dual turbocharging system is implemented, especially in multi-cylinder engines. Such systems require a very complex pipeline to eliminate the interference of the exhaust pulses between the adjacent cylinder ignitions. In this study, the two-stage, multi-channel turbine system was investigated for two different rotor geometries: the old, high-performance rotor A and the smaller but more modern rotor B, which was scaled to match rotor A. Both geometries were compared at three different turbine speeds and variable turbine geometry (VTG) vane positions. It was found that the two-stage turbine system with rotor B geometry provided an 8% higher total efficiency than rotor A due to the lower flow losses within the rotor passage. [ABSTRACT FROM AUTHOR]

In the present study, a 100 kW organic Rankine cycle is suggested to recover heat energy from commercial ships. A radial-type turbine is employed with R1233zd(E) and back-to-back layout. To improve the performance of an organic Rankine power system, the efficiency of the turbine is significant. With the conventional approach, the optimization of a turbine requires a considerable amount of time and involves substantial costs. By combining design of experiments, an artificial neural network, and Latin hypercube sampling, it becomes possible to reduce costs and achieve rapid optimization. A radial basis neural network with machine learning technique, known for its advantages of being fast and easily applicable, has been implemented. Using such an approach, an increase in efficiency greater than 1% was achieved with minimal design changes at the first and second turbines.

To address the increasing interest towards more environmentally friendly naval transportation and the introduction of IMO2020 restrictions on pollutant emissions onboard ships, the present work details the preliminary design of a mini gas turbine engine, i.e., a gas turbine engine with an output power up to 5 MW, for onboard energy generation. In comparison to conventional propulsion systems, gas turbine units benefit from known compactness, which can be further enhanced by employing single-stage uncooled radial machines, according to similar works in the field. As such, the present paper aims to set up a complete procedure that allows a reliable and fast (i.e., requiring a limited computational effort) preliminary design of one-stage centrifugal compressors and radial turbines operating at a high pressure ratio via the use of classical one-dimensional theory. The aerodynamic design outputs in terms of forces and torques are then used to perform a preliminary mechanical design of the shaft by means of a one-dimensional finite element model with commercial software to estimate the corresponding shaft line stress. Despite some necessary geometrical and modeling simplification of the design problem, which results in the unavailability of detailed information on individual components, the employed procedure nevertheless allows a comprehensive overview of the possibilities in terms of maximum machine performance achievable at an early design stage with the associated limited computational requirements. The design procedure and the geometry achieved for the application are presented along with aerodynamic and structural results. [ABSTRACT FROM AUTHOR]

The air-management system of a proton exchange membrane fuel cell (PEMFC) is responsible for supplying the fuel cell stack with ambient air at appropriate conditions. The compressor of the air-management system can be partly driven by utilizing the fuel cell exhaust gas in a turbine. The fuel cell exhaust is partially or fully saturated with water vapor. When the exhaust gas is expanded in the turbine, supersaturation occurs. This leads to the nucleation of droplets and their subsequent growth by condensation. This study provides an overview and understanding of the various phenomena caused by condensation and liquid water in the turbine of a PEMFC air-management system. The basis for this work is previously published numerical simulations that focused on individual aspects of the above phenomena. The present work revisits these results and puts them in context to provide a comprehensive understanding. Important phenomena are the effects of condensation on turbine performance through phase change losses, release of latent heat and thermal throttling. In addition, the released latent heat offers a power potential for downstream turbine stages. Through these effects, condensation can also impact the entire air-management system. However, condensation may occur unevenly, causing a circumferential asymmetry of the turbine outflow. Liquid water in the turbine can lead to droplet erosion, corrosion, and water-induced damage. In summary, it is essential to consider condensation and liquid water when developing turbines for PEMFC air-management systems. [ABSTRACT FROM AUTHOR]

This work presents the development and application of a machine learning model to predict the unsteady performance of a turbocharger radial turbine subject to on-engine pulsating flow conditions. The model proposed, based on a fully connected neural network, predicts the instantaneous turbine torque and circumferentially-averaged relative inflow angle when given, as only inputs, the total pressure and temperature pulses and the time derivative of the total pressure pulse upstream of the turbine.The training data set for the model is obtained from an experimentally-validated Reynolds-averaged Navier–Stokes model and consists of various operating conditions characterized by different pulse amplitudes and frequencies. Heat transfer effects are neglected by the use of adiabatic boundary conditions while the rotational speed of the rotor is otherwise maintained fixed. Based on the results obtained, the model is shown capable of accurately predicting the turbine torque and local properties of the flow, such as the relative inflow angle, with a high degree of accuracy (coefficient of determination larger than 0.98). At first, the model is tested for both interpolation and extrapolation conditions. Given a training data set constituted by only three pulses characterized by different amplitudes, the model accurately predicts the turbine performance both for conditions inside and outside the range of amplitudes of the training data set. Lastly, the model is trained with a larger data set, including both variations of the pulse amplitude and frequency, in order to predict the performance of the turbine subject to a more general pulse shape. The error indicators show an improvement with respect to the extrapolation case due to the larger size of the training data set, showing also a great capability of the model to predict the unsteady performance of the turbine for a more general pulse shape. The model represents a fast and efficient approach for predicting the unsteady turbine performance as compared to more complex experimental set-ups and time-consuming 3D numerical simulations and a valid alternative to the more common 0D-1D models.

The widespread trend of pursuing higher efficiencies in radial turbochargers led to the prompting of this work. A 3D-printed model of the static parts of a radial variable geometry turbine, the vaned nozzle, and the volute, was developed. This model was up-scaled from the actual reference turbine to place sensors and characterize the flow around the nozzle vanes, including the tip gap. In this study, a computational model of the scaled-up turbine was carried out to verify the results in two ways. For this model, firstly compared with an already validated CFD turbine model of the real device (which includes a rotor), its operating range was extended to different nozzle positions, and we checked the issues with rotor–stator interactions as well as the influence of elements such as the screws of the turbine stator. After showing results for different nozzle openings, another purpose of the study was to check the effect of varying the clearance over the tip of the stator vanes on the tip leakage flow since the 3D-printed model has variable gap height configurations. [ABSTRACT FROM AUTHOR]

• A jet impingement cooling technology for radial turbines was proposed. • The temperature distribution on the surface of a rotating turbine was measured using an IR camera. • The wall temperature of the turbo wheel could be significantly reduced by consuming acceptable mass flow rates of the coolant. • The temperature distribution periodically fluctuates under the combined effects of cooling, rotation, and thermal inertia. Increasing the inflow temperature of a turbine is an effective approach for enhancing the thermal efficiency of devices operating in the Brayton cycle, such as micro-gas-turbines and waste heat recovery systems. However, elevated temperatures also pose a significant risk of thermal fatigue failure. This paper presents an experimental investigation of impingement cooling for radial turbines, aiming to achieve high cooling performance with a simple structure. High-frequency infrared thermal imaging technology was employed to measure temperature distribution in the turbine rotor under various operational conditions. The results indicate that jet-impingement cooling can substantially reduce the solid temperature of the radial turbine, with a maximum temperature reduction of approximately 44 K achieved by consuming the coolant with ṁ re = 5%. Increasing the mass flow rate of the coolant consistently lowers the rotor temperature; however, an increase in rotational speed results in higher thermal inertia, thereby diminishing the cooling enhancement effect. The temperature distribution on the turbine surface exhibits significant periodic characteristics over time, leading to temperature fluctuations of 5 K to 30 K at the hub position. Furthermore, the cooling performance is further enhanced near the jet hole on the back-disc side of the inducer region, while the tip side closer to the exducer obtains better cooling effects. [ABSTRACT FROM AUTHOR]

The organic Rankine cycle (ORC) is an efficient technology for electricity generation from low- and medium-temperature heat sources. In this type of power cycle, the radial inflow turbine is the option usually selected for electricity generation. As a critical ORC component, turbine performance markedly affects the efficiency of the system. Therefore, the challenge is to model the behavior of the radial inflow turbine operating with organic fluids for heat recovery applications. In this context, various groups of fluids are highlighted in the scientific literature, including R-123, R-245fa, and R-141b, which are the fluids used in this research. Since little research has focused on the turbine efficiency effect on the power cycle design and analysis, this study presents an analysis of a radial inflow turbine based on a mathematical model of a one-dimensional design of the turbine. From this analysis, geometric, thermal, and operating parameters were determined, as well as volute, stator, and rotor losses. For this purpose, an algorithm was implemented in MATLAB to calculate the one-dimensional parameters of the turbine. Using these parameters, a 3D model of the turbine was designed in ANSYS-CFX, with performance curves of each projected turbine under design and off-design conditions. The numerical results suggest that the isentropic efficiency of all the proposed turbines under design conditions can surpass 75%. Additionally, the findings indicate that different design conditions, such as specific speed, pressure ratio, and turbine size, can affect the efficiency of radial inflow turbines in ORC systems.

Organic Rankine cycle (ORC) is an effective technology to harness low-grade energy. Turbine, as a key component of ORC, takes advantages of its high efficiency and compact size compared with other expanders. Currently, developing suitable turbines with a high performance and a low cost is one of the bottlenecks for wide applications of various ORCs. In this context, technical progress on radial inflow turbines (RITs), axial turbines (ATs), and radial outflow turbines (ROTs) is introduced, and loss models used in the preliminary design are compared, especially for small-scale ORCs. RIT is recommended for medium and small ORCs with an expansion pressure ratio of

The efficiency of hybrid electric vehicles may be substantially increased if the energy of exhaust gases, which do not complete the expansion inside the cylinder of the internal combustion engine, is efficiently recovered using a properly designed turbo-generator and employed for vehicle propulsion. Previous studies, carried out by the same authors of this work, showed a potential hybrid vehicle fuel efficiency increment up to 15% employing a 20 kW turbine on a 100 HP-rated power thermal unit. The innovative thermal unit proposed here is composed of a supercharged engine endowed with a properly designed turbo-generator, which comprises two fundamental elements: an exhaust gas turbine expressly designed and optimized for the application, and a suitable electric generator necessary to convert the recovered energy into electric energy, which can be stored in the on-board energy storage system of the vehicle. In this two-part work, the realistic efficiency of the innovative thermal unit for hybrid vehicles is evaluated and compared to a traditional turbocharged engine. In Part 1, the authors presented a model for the prediction of the efficiency of a dedicated radial turbine, based on a simple but effective mean-line approach; the same paper also reports a design algorithm, which, thanks to some assumptions and approximations, allows fast determination of the right turbine geometry for a given design operating condition. It is worth pointing out that, being optimized for quasi-steady power production, the exhaust gas turbine here considered is quite different from the ones commonly employed for turbocharging applications; for this reason, and in consideration of the required power size, such a turbine is not available on the market, nor has its development been previously carried out in the scientific literature. In this paper, Part 2, a radial turbine geometry is defined for the thermal unit previously calculated, employing the design algorithm described in Part 1; the realistic energetic advantages that could be achieved by the implementation of the turbo-generator on a hybrid propulsion system are evaluated through the performance prediction model under different operating conditions of the thermal unit. As an overall result, it was estimated that, compared to a reference traditional turbocharged engine, the turbo-compound system could gain vehicle efficiency improvement between 3.1% and 17.9%, according to the output power delivered, with an average efficiency increment of 10.9% evaluated on the whole operating range.

Internal combustion engine (ICE) exhaust gases provide a high amount of energy which is partially lost to the environment. Such energy can be recovered with a turbocharger turbine or other after-treatment device. As the engine exhaust flow varies not only with the engine load but also with the opening and closing of the exhaust valves, a proper matching between the engine and the turbine should be established to maximize the recovery of waste energy. That is why a twin-scroll or dual turbocharging system is implemented, especially in multi-cylinder engines. Such systems require a very complex pipeline to eliminate the interference of the exhaust pulses between the adjacent cylinder ignitions. In this study, the two-stage, multi-channel turbine system was investigated for two different rotor geometries: the old, high-performance rotor A and the smaller but more modern rotor B, which was scaled to match rotor A. Both geometries were compared at three different turbine speeds and variable turbine geometry (VTG) vane positions. It was found that the two-stage turbine system with rotor B geometry provided an 8% higher total efficiency than rotor A due to the lower flow losses within the rotor passage.

To address the increasing interest towards more environmentally friendly naval transportation and the introduction of IMO2020 restrictions on pollutant emissions onboard ships, the present work details the preliminary design of a mini gas turbine engine, i.e., a gas turbine engine with an output power up to 5 MW, for onboard energy generation. In comparison to conventional propulsion systems, gas turbine units benefit from known compactness, which can be further enhanced by employing single-stage uncooled radial machines, according to similar works in the field. As such, the present paper aims to set up a complete procedure that allows a reliable and fast (i.e., requiring a limited computational effort) preliminary design of one-stage centrifugal compressors and radial turbines operating at a high pressure ratio via the use of classical one-dimensional theory. The aerodynamic design outputs in terms of forces and torques are then used to perform a preliminary mechanical design of the shaft by means of a one-dimensional finite element model with commercial software to estimate the corresponding shaft line stress. Despite some necessary geometrical and modeling simplification of the design problem, which results in the unavailability of detailed information on individual components, the employed procedure nevertheless allows a comprehensive overview of the possibilities in terms of maximum machine performance achievable at an early design stage with the associated limited computational requirements. The design procedure and the geometry achieved for the application are presented along with aerodynamic and structural results.

The air-management system of a proton exchange membrane fuel cell (PEMFC) is responsible for supplying the fuel cell stack with ambient air at appropriate conditions. The compressor of the air-management system can be partly driven by utilizing the fuel cell exhaust gas in a turbine. The fuel cell exhaust is partially or fully saturated with water vapor. When the exhaust gas is expanded in the turbine, supersaturation occurs. This leads to the nucleation of droplets and their subsequent growth by condensation. This study provides an overview and understanding of the various phenomena caused by condensation and liquid water in the turbine of a PEMFC air-management system. The basis for this work is previously published numerical simulations that focused on individual aspects of the above phenomena. The present work revisits these results and puts them in context to provide a comprehensive understanding. Important phenomena are the effects of condensation on turbine performance through phase change losses, release of latent heat and thermal throttling. In addition, the released latent heat offers a power potential for downstream turbine stages. Through these effects, condensation can also impact the entire air-management system. However, condensation may occur unevenly, causing a circumferential asymmetry of the turbine outflow. Liquid water in the turbine can lead to droplet erosion, corrosion, and water-induced damage. In summary, it is essential to consider condensation and liquid water when developing turbines for PEMFC air-management systems.

Radial turbines used in automotive fuel cell turbochargers operate with humid air. The gas expansion in the turbine causes droplets to form, which then grow through condensation. The associated release of latent heat and decrease in the gaseous mass flow strongly influence the thermodynamics of the turbine. This study aims to investigate these phenomena. For this purpose, the classical nucleation theory and Young's growth law are integrated into a Euler-Lagrange approach. The main advantages of this approach are the calculation of individual droplet trajectories and a full resolution of the droplet spectrum. The results indicate an onset of nucleation at the blade tip and in the tip gap, followed by nucleation over the entire blade span, depending on the humidity at the turbine inlet. With a saturated turbine inflow, condensation causes the outlet temperature to rise to almost the same level as at the inlet. In addition, condensation losses reduce the efficiency and the latent heat released by condensation leads to significant thermal throttling. [ABSTRACT FROM AUTHOR]

The work arose initially from an interest in design of radial turbine for small scale gas turbine applications typically suitable for distributed power generation system which demands compact installations. The paper describes an investigation in to the design and performance of radial inflow turbines having a capacity of 25kW at 1,50,000 rpm. First a non-dimensional design philosophy is deduced to design a turbine rotor. The design approach is largely one dimensional along with empirical correlations for estimating losses used to obtain the main geometric parameters of turbine. From the proposed design approach, turbine total-to-static efficiency is calculated as 84.91% which is reasonably good. After that a modified vortex design procedure is developed to derive the non-dimensional volute geometry as a function of azimuth angle for actual flow condition. Once a specific turbine is designed, the flow is analyzed in detail using a three-dimensional Computational Fluid Dynamics (CFD) code in order to assess how accurately the performance is predicted by simple meanline analysis. Finally, a fully instrumented experimental setup is developed. The experimental investigations have been carried out to study the temperature and pressure distribution across turbine and total-to-static efficiency is calculated. The limitations of surging and choking in compressor as well as in the bearings to take up load at such high speed has allowed the tests to be conducted upto 70000 rpm only, with turbine inlet temperatures ranging from 900 K to 1000 K and a pressure ratio upto 1.79, which developed power in the range of 1.69 kW to 10.22 kW. The uncertainty bands are in order of ±13.76% to ±3.12%. It is observed that the CFD results are in good agreement with test results at off design condition. CFD models over predicted total to static efficiency by order of 7-8% at lower speed. These deviations are reduced as turbine runs close to design point.

The widespread trend of pursuing higher efficiencies in radial turbochargers led to the prompting of this work. A 3D-printed model of the static parts of a radial variable geometry turbine, the vaned nozzle, and the volute, was developed. This model was up-scaled from the actual reference turbine to place sensors and characterize the flow around the nozzle vanes, including the tip gap. In this study, a computational model of the scaled-up turbine was carried out to verify the results in two ways. For this model, firstly compared with an already validated CFD turbine model of the real device (which includes a rotor), its operating range was extended to different nozzle positions, and we checked the issues with rotor–stator interactions as well as the influence of elements such as the screws of the turbine stator. After showing results for different nozzle openings, another purpose of the study was to check the effect of varying the clearance over the tip of the stator vanes on the tip leakage flow since the 3D-printed model has variable gap height configurations.

This paper addresses the problem of the design optimization of turbomachinery components under thermo-mechanical constraints, with focus on a radial turbine impeller for turbocharger applications. Typically, turbine components operate at high temperatures and are exposed to important thermal gradients, leading to thermal stresses. Dealing with such structural requirements necessitates the optimization algorithms to operate a coupling between fluid and structural solvers that is computationally intensive. To reduce the cost during the optimization, a novel multiphysics gradient-based approach is developed in this work, integrating a Conjugate Heat Transfer procedure by means of a partitioned coupling technique. The discrete adjoint framework allows for the efficient computation of the gradients of the thermo-mechanical constraint with respect to a large number of design variables. The contribution of the thermal strains to the sensitivities of the cost function extends the multidisciplinary outlook of the optimization and the accuracy of its predictions, with the aim of reducing the empirical safety factors applied to the design process. Finally, a turbine impeller is analyzed in a demanding operative condition and the gradient information results in a perturbation of the grid coordinates, reducing the stresses at the rotor back-plate, as a demonstration of the suitability of the presented method. [ABSTRACT FROM AUTHOR]

This paper presents results of strain gauge measurements, which have been carried out on a full-scale turbocharger test rig. Rotational speed of the turbocharger was ramped up and down through four preliminary anticipated rotor-blade resonances, with a known combination of main order of excitation and corresponding nodal diameter. An analysis of the transient data is presented. An investigation of spectra with high frequency resolutions, centered on individual blade resonance points in time, is presented. In contrast to former research, all blades resonate at the same point in time and thus at the same resonance frequency, if the excitation corresponds to a nodal diameter of zero. Strain data from the shaft is used to support findings, which, in other publications, often solely rely on strain data from individual blades. [ABSTRACT FROM AUTHOR]

A turbocharger's radial turbine has a strong impact on the fuel consumption and transient response of internal combustion engines. This paper summarizes the efforts to design a new radial turbine aiming at high efficiency and low inertia by applying two different optimization techniques to a parametrized CAD model. The first workflow wraps 3D fluid and solid simulations within a meta-model assisted genetic algorithm to find an efficient turbine subjected to several constraints. In the next step, the chosen turbine is re-parametrized and fed into the second workflow which makes use of a gradient projection algorithm to further fine-tune the design. This requires the computation of gradients with respect to the CAD parametrization, which is done by calculating and combining surface sensitivities and design velocities. Both methods are applied successfully, i.e., the first delivers a well-performing turbine, which, by the second method, is further improved by 0.34% in efficiency. [ABSTRACT FROM AUTHOR]

This paper presents the design procedure and analysis of a radial turbine design for a mid-scale supercritical CO 2 power cycle. Firstly, thermodynamic analysis of a mid-range utility-scale cycle, similar to that proposed by NET Power, is established while lowering the turbine inlet temperature to 900 ∘ C in order to remove cooling complexities within the radial turbine passages. The cycle conditions are then considered for the design of a 100 MW t h power scale turbine by using lower and higher fidelity methods. A 510 mm diameter radial turbine, running at 21,409 rpm, capable of operating within a 5% range of the required cycle conditions, is designed and presented. Results from computational fluid dynamics simulations indicate the loss mechanisms responsible for the low-end value of the turbine total-to-total efficiency which is 69.87%. Those include shock losses at stator outlet, incidence losses at rotor inlet, and various mixing zones within the passage. Mechanical stress calculations show that the current blade design flow path of the rotor experiences tolerable stress values, however a more detailed re-visitation of disc design is necessitated to ensure an adequate safety margin for given materials. A discussion of the enabling technologies needed for the adoption of a mid-size radial turbine is given based on current advancements in seals, bearings, and materials for supercritical CO 2 cycles. [ABSTRACT FROM AUTHOR]

Radial turbines used in automotive fuel cell turbochargers operate with humid air. The gas expansion in the turbine causes droplets to form, which then grow through condensation. The associated release of latent heat and decrease in the gaseous mass flow strongly influence the thermodynamics of the turbine. This study aims to investigate these phenomena. For this purpose, the classical nucleation theory and Young’s growth law are integrated into a Euler–Lagrange approach. The main advantages of this approach are the calculation of individual droplet trajectories and a full resolution of the droplet spectrum. The results indicate an onset of nucleation at the blade tip and in the tip gap, followed by nucleation over the entire blade span, depending on the humidity at the turbine inlet. With a saturated turbine inflow, condensation causes the outlet temperature to rise to almost the same level as at the inlet. In addition, condensation losses reduce the efficiency and the latent heat released by condensation leads to significant thermal throttling.

The design of optimal organic Rankine cycle (ORC) systems requires the simultaneous identification of the optimal cycle architecture, operating conditions and working fluid, whilst accounting for the effect of these parameters on expander performance. In this paper, a novel method for predicting the design-point efficiency of a radial turbine is developed, which can predict the achievable efficiency based only on the thermodynamic conditions. This model is integrated into an optimization framework in which the working fluid is modeled using the Peng-Robinson equation of state and the fluid parameters (i.e., critical temperature) are simultaneously optimized alongside the cycle conditions. This framework can evaluate recuperated and transcritical cycles, whilst heat-transfer area requirements are estimated based on representative overall heat-transfer coefficients. For a range of heat sources, a single-objective optimization is first completed in which power output is maximized, which is then followed by a multi-objective optimization in which the trade-off between power output and total heat-transfer area is investigated. It is demonstrated that the optimization framework can simultaneously optimize the working fluid and cycle parameters, and identify whether a subcritical or transcritical cycle, with or without a recuperator, is best suited for a particular application, whilst accounting for the effect of these variables on the expander performance. This information is critical to identify optimal cycle configurations and working fluids that result in the best thermodynamic performance, yet exist in the design space in which feasible turbines can be designed. It is found that the optimal critical temperature does not vary significantly between different cycle architectures, and is not affected by whether a single or multi-objective optimization is completed. However, including the expander performance model results in significantly different cycles to optimal thermodynamic cycles.

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.

In turbocharger design, the accurate determination of thermally induced stresses is of particular importance for life cycle predictions. An accurate, transient, thermal finite element analysis (FEA) of turbocharger components requires transient conjugate heat transfer (CHT) analysis. However, due to the vastly different timescales of the heat transfer mechanisms in fluid and in solid states, unsteady CHT simulations are burdened by high computational costs. Hence, for design iterations, uncoupled CFD and FEA approaches are needed. The quality of the uncoupled thermal analysis depends on the local heat transfer coefficients (HTC) and reference fluid temperatures. In this paper, multiple CFD-FEA methods known from literature are implemented in a numerical model of a turbocharger. In order to describe the heat transfer and thermal boundary layer of the fluid, different definitions of heat transfer coefficients and reference fluid temperatures are investigated with regard to calculation time and accuracy. For the transient simulation of a long heating process, the combination of the CFD-FEA methods with the interpolation FEA approach is examined. Additionally, a structural-mechanical analysis is conducted. The results of the developed methods are evaluated against experimental data and the results of the extensive unsteady CHT numerical method. [ABSTRACT FROM AUTHOR]

The work arose initially from an interest in design of radial turbine for small scale gas turbine applications typically suitable for distributed power generation system which demands compact installations. The paper describes an investigation in to the design and performance of radial inflow turbines having a capacity of 25kW at 1,50,000 rpm. First a non-dimensional design philosophy is deduced to design a turbine rotor. The design approach is largely one dimensional along with empirical correlations for estimating losses used to obtain the main geometric parameters of turbine. From the proposed design approach, turbine total-to-static efficiency is calculated as 84.91% which is reasonably good. After that a modified vortex design procedure is developed to derive the non-dimensional volute geometry as a function of azimuth angle for actual flow condition. Once a specific turbine is designed, the flow is analyzed in detail using a three-dimensional Computational Fluid Dynamics (CFD) code in order to assess how accurately the performance is predicted by simple meanline analysis. Finally, a fully instrumented experimental setup is developed. The experimental investigations have been carried out to study the temperature and pressure distribution across turbine and total-to-static efficiency is calculated. The limitations of surging and choking in compressor as well as in the bearings to take up load at such high speed has allowed the tests to be conducted upto 70000 rpm only, with turbine inlet temperatures ranging from 900 K to 1000 K and a pressure ratio upto 1.79, which developed power in the range of 1.69 kW to 10.22 kW. The uncertainty bands are in order of ±13.76% to ±3.12%. It is observed that the CFD results are in good agreement with test results at off design condition. CFD models over predicted total to static efficiency by order of 7-8% at lower speed. These deviations are reduced as turbine runs close to design point. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Highlights • Design of a radial turbine for the 20 kW micro gas turbine. • Radial turbine through-flow analysis and comparison of 1D and CFD results. • Optimization of the turbine geometry using an inverse design method. • Performance improvement by introducing a unique double curvature turbine blade. • Turbine mechanical qualification and aerodynamic performance estimation. Abstract The paper reports a study on the design of a radial turbine for a portable micro gas turbine engine. A unique design of blades with double curvatures is proposed which demonstrates the considerable advantage in terms of efficiency and power output. The design process largely consists of design, optimization, and analysis of radial turbine closely based on low mass flow rate and high-pressure ratio. The intention of the development is to achieve reductions both in fuel consumption and emissions. The micro gas turbine engine is designed to generate 20 kW net power output. As a 110 mm centrifugal compressor takes 56 kW power in the Brayton cycle, a 113 mm inlet diameter radial turbine is designed to produce 76 kW power. Optimization of the initial turbine geometry is carried out using an inverse design technique to improve the overall turbine stage performance. The original turbine blade meridional frame was used as an input to the optimization. The optimized 3-D blade geometry have a unique double curvature blade sections which is unlikely to be achieved using the conventional design approach. The performance of the optimized geometry has been compared with that of the initial geometry. Computational fluid dynamic and finite element analysis techniques were used for examining the aerodynamic performance and structural integrity respectively. The rotational speed of the turbine was set up to 101,400 RPM. The result of computational dynamic analysis indicates that the optimized geometry provides an approximately 6% increase in total-to-static efficiency on average and 6 kW increase in power output at high expansion ratio as compared to the original design. Stress analysis shows that the maximum stress is lower than the yield strength of the material, which verifies that the turbine design is mechanically viable. [ABSTRACT FROM AUTHOR]

Solar chimney power plants (SCPPs) collect air heated over a large area on the ground and exhaust it through a turbine or turbines located near the base of a tall chimney to produce renewable electricity. SCPP design in practice is likely to be specific to the site and of variable size, both of which require a purpose-built turbine. If SCPP turbines cannot be mass produced, unlike wind turbines, for example, they should be as cheap as possible to manufacture as their design changes. It is argued that a radial inflow turbine with blades made from metal sheets, or similar material, is likely to achieve this objective. This turbine type has not previously been considered for SCPPs. This article presents the design of a radial turbine to be placed hypothetically at the bottom of the Manzanares SCPP, the only large prototype to be built. Three-dimensional computational fluid dynamics (CFD) simulations were used to assess the turbine’s performance when installed in the SCPP. Multiple reference frames with the renormalization group k-ε turbulence model, and a discrete ordinates non-gray radiation model were used in the CFD simulations. Three radial turbines were designed and simulated. The largest power output was 77.7 kW at a shaft speed of 15 rpm for a solar radiation of 850 W/m2 which exceeds by more than 40 kW the original axial turbine used in Manzanares. Further, the efficiency of this turbine matches the highest efficiency of competing turbine designs in the literature.

This paper addresses the problem of the design optimization of turbomachinery components under thermo-mechanical constraints, with focus on a radial turbine impeller for turbocharger applications. Typically, turbine components operate at high temperatures and are exposed to important thermal gradients, leading to thermal stresses. Dealing with such structural requirements necessitates the optimization algorithms to operate a coupling between fluid and structural solvers that is computationally intensive. To reduce the cost during the optimization, a novel multiphysics gradient-based approach is developed in this work, integrating a Conjugate Heat Transfer procedure by means of a partitioned coupling technique. The discrete adjoint framework allows for the efficient computation of the gradients of the thermo-mechanical constraint with respect to a large number of design variables. The contribution of the thermal strains to the sensitivities of the cost function extends the multidisciplinary outlook of the optimization and the accuracy of its predictions, with the aim of reducing the empirical safety factors applied to the design process. Finally, a turbine impeller is analyzed in a demanding operative condition and the gradient information results in a perturbation of the grid coordinates, reducing the stresses at the rotor back-plate, as a demonstration of the suitability of the presented method.

A turbocharger’s radial turbine has a strong impact on the fuel consumption and transient response of internal combustion engines. This paper summarizes the efforts to design a new radial turbine aiming at high efficiency and low inertia by applying two different optimization techniques to a parametrized CAD model. The first workflow wraps 3D fluid and solid simulations within a meta-model assisted genetic algorithm to find an efficient turbine subjected to several constraints. In the next step, the chosen turbine is re-parametrized and fed into the second workflow which makes use of a gradient projection algorithm to further fine-tune the design. This requires the computation of gradients with respect to the CAD parametrization, which is done by calculating and combining surface sensitivities and design velocities. Both methods are applied successfully, i.e., the first delivers a well-performing turbine, which, by the second method, is further improved by 0.34% in efficiency.

This paper presents results of strain gauge measurements, which have been carried out on a full-scale turbocharger test rig. Rotational speed of the turbocharger was ramped up and down through four preliminary anticipated rotor-blade resonances, with a known combination of main order of excitation and corresponding nodal diameter. An analysis of the transient data is presented. An investigation of spectra with high frequency resolutions, centered on individual blade resonance points in time, is presented. In contrast to former research, all blades resonate at the same point in time and thus at the same resonance frequency, if the excitation corresponds to a nodal diameter of zero. Strain data from the shaft is used to support findings, which, in other publications, often solely rely on strain data from individual blades.

This paper presents the design procedure and analysis of a radial turbine design for a mid-scale supercritical CO 2 power cycle. Firstly, thermodynamic analysis of a mid-range utility-scale cycle, similar to that proposed by NET Power, is established while lowering the turbine inlet temperature to 900 ∘ C in order to remove cooling complexities within the radial turbine passages. The cycle conditions are then considered for the design of a 100 MW t h power scale turbine by using lower and higher fidelity methods. A 510 mm diameter radial turbine, running at 21,409 rpm, capable of operating within a 5% range of the required cycle conditions, is designed and presented. Results from computational fluid dynamics simulations indicate the loss mechanisms responsible for the low-end value of the turbine total-to-total efficiency which is 69.87%. Those include shock losses at stator outlet, incidence losses at rotor inlet, and various mixing zones within the passage. Mechanical stress calculations show that the current blade design flow path of the rotor experiences tolerable stress values, however a more detailed re-visitation of disc design is necessitated to ensure an adequate safety margin for given materials. A discussion of the enabling technologies needed for the adoption of a mid-size radial turbine is given based on current advancements in seals, bearings, and materials for supercritical CO 2 cycles.

Looking at the waste heat potential made available by industry, it can be noted that there are many sectors where small scale (< 100 kWe) organic Rankine cycle (ORC) plants could be applied to improve the energy efficiency. Such plants are quite challenging from the techno-economic point of view: the temperature of the primary heat source poses a low cutoff to the system thermodynamic efficiency. Therefore, high-performance components are needed, but, at the same time, they have to be at low cost as possible to assure a reasonable payback time. In this paper, the design of a two-stage radial in-flow turbine for small ORC industrial plants is presented. Compared to commonly applied mono-stage expanders (both volumetric and dynamic), this novel turbine enables plants to exploit higher pressure ratios than conventional plants. Thus, the theoretical limit to the cycle efficiency is enhanced with undoubted benefits on the overall ORC plant performance. The design process involved 1D/2D models as well as 3D Computational Fluid Dynamic ones. After the design of the preliminary configuration, sensitivity analyses were carried out varying the most relevant geometric parameters for design performance improvement. Thereafter, the stages were both analyzed in off-design conditions giving their performance maps. Moreover, a stage stacking procedure was applied to obtain the overall turbine behavior.

The pressure gradient in the dual volute radial turbocharger turbines is the primary source of the vortices' formation in rotor passages. The effects of the upstream non-uniform flow conditions on the development of secondary flows are not well known. In this study, the effect of highly skewed and non-uniform mass flow on the secondary vortices in different admission cases in a dual entry turbine was investigated using CFD modeling. The results agree well with the experiment, and show that increasing the inequality of the pressure between the entries leads to a reduction in the turbine's performance. Some useful energy dissipates due to mixing the flows of the entries. Isolating the rotor sectors in the tongues region was applied with the purpose of limiting the mixing. Also, the vortices' behavior in the rotor passages with different surface pressure ratios for the passage sides were investigated for both equal and partial admission. The surface pressure of the airfoil pressure side was more effective on the tip and trailing edge vortex than the suction side, while the leading-edge root vortex did not change by any variation in the surface pressure ratio. The vortices' center location shifted with the pressure variation, and consequently, by decreasing the pressure level, the center of the tip vorticity turned to the upstream sections, and the leading-edge root vortex center moved closer to the pressure side. [ABSTRACT FROM AUTHOR]

This paper is focussed on the development of an axial inflow turbocharger turbine as a viable alternative to a baseline radial turbine for certain applications. Additionally a variable geometry turbine (VGT) technology is incorporated into the axial-inflow turbine to additionally benefit both efficiency and performance. The developed turbine was compared to the baseline in terms of engine performance, fuel consumption and emissions. The design and optimisation of the inlet casing, stator and rotor blades for axial inflow turbine were developed through CFD simulation. Then a VGT system was further developed, equipped with pivoting stator blades. Necessary data at various flow conditions were collected for engine modelling to test the engine performance achieved by the integration of the axial turbine, which achieved a maximum 86.2% isentropic efficiency at 102,000 rpm. The paper further focussed on the design and optimization of a volute for axial inflow turbine. Various initial designs were tested using CFD simulations and the chosen configuration was optimised further to improve overall stage efficiency, which reached 81.2%. Engine model simulations demonstrated that engine power and torque are significantly increased through the application of the proposed variable geometry axial turbocharger turbine. [ABSTRACT FROM AUTHOR]