Performance Of Radial Turbine Research Articles

An investigation of the effects of volute A/R distribution on radial turbine performance

In order to meet the higher design requirements of radial turbines, it is necessary to clearly understand the impact of different design parameters on turbine performance. The A/R distribution is one of the most important design parameters for the radial turbine volute, but there are few studies on it. To clarify the effect of A/R distribution on turbine efficiency and blade excitation force, a detailed comparative study is carried out. An experimentally validated numerical method is used, and steady and unsteady CFD simulations are conducted in this study. The results show that the volute A/R distribution has a significant effect on the turbine efficiency, while a linear distribution can provide a more uniform inlet condition and thus improve the rotor efficiency. The flow parameters fluctuated significantly at the volute tongue. Although the efficiency is not sensitive to this fluctuation, it directly affects the excitation force on the rotor blades. The volute with S-shaped A/R distribution produces the smallest excitation force due to the smallest fluctuation. Two new A/R distributions are presented which combine the advantages of linear and S-shaped or convex A/R distributions with high efficiency and low excitation force. It is suggested that the A/R should be close to the linear distribution and decreases rapidly before the tongue.

Using Machine Learning for Loss Prediction in a Hybrid Meanline Modeling Method to Deliver Improved Radial Turbine Performance Prediction

Abstract Low fidelity modeling approaches remain attractive due to an unrivaled ability to predict full turbine performance maps quickly compared to high-fidelity approaches such as computational fluid dynamics (CFD), especially in the preliminary design process. As improvements in performance on a component level approach a point of diminishing returns, the ability to efficiently optimize the complete charging system for a given duty is a topic attracting significant research interest. In the case of turbocharging applications, existing engine and powertrain simulations require turbine maps to calculate the turbine performance, which are usually obtained from experimental testing. Unfortunately, the need for extrapolation is unavoidable because of the limited range of testing data available, leading to inaccuracies especially at off-design conditions. To enable intensive modeling and optimization of complete vehicle powertrains for different drive cycles, the current piece of work seeks to combine the advantages of machine learning techniques and physical meanline modeling to facilitate faster, more accurate predictions of complete turbocharger maps. This paper presents a novel methodology for turbocharger turbine rotor and nozzle performance prediction based on hybrid modeling. The turbine rotor and nozzle were parameterized to conduct CFD simulations for a wide variety of turbine geometries, which were used to form a database to train an artificial neural network (ANN). The predicted losses provided by the ANN were then utilized in the meanline code, substituting for the conventional empirical loss models. As well as removing the need for empirical loss models, modifications were undertaken to the meanline approach to further enhance modeling accuracy. First, in order to accurately characterize the stage mass flow capacity, the losses occurring in the nozzle and rotor were subdivided into those occurring before and after the throat. A second novel aspect is that the aerodynamic blockage level at the rotor throat was implemented as a variable rather than a constant value. By training the ANN to predict the variation of blockage with geometry and operating condition, a more accurate depiction of the changing secondary flow fields could be achieved. The capabilities of the hybrid meanline modeling method were evaluated on several unseen test cases. The resulting predictions of efficiency and mass flowrate demonstrated strong correlation with CFD results and experimental test results. The hybrid meanline modeling method therefore displays great potential in wide range radial turbine performance prediction with enhanced accuracy in comparison to traditional approaches.

Influence of trailing edge curve on the performance of radial turbine in turbocharger

Abstract To combat climate change and promote sustainable engine development, the optimization of the turbocharger development process is necessary to decrease emissions and increase fuel economy. This article presents the influence of trailing edge curves on the performance of the significantly small radial turbine impeller of an automotive turbocharger used in a 0.8-l two-cylinder gasoline engine by comparing numerical analysis results under two boundary conditions: a constant pressure ratio and constant mass flow rate. The curve of a trailing edge depends on several parameters; however, in this study, the exponent ($n$) was selected to modify the turbine impeller trailing edge profile, as it exhibits a more significant influence on the curve than other parameters. Hence, computational fluid dynamics analyses were conducted on the radial turbine for various trailing edge curves under a constant pressure ratio and constant mass flow rate, and the results were compared. The results indicated that the efficiency improvement was negligible under the pressure ratio and mass flow rate conditions due to inadequate alterations. Nevertheless, a significant shaft power improvement was observed based on changes in the trailing edge curve under a constant pressure ratio. In contrast, the same changes caused a considerable decrease in the shaft power under a constant mass flow rate.

Modeling radial turbine performance under pulsating flow by machine learning method

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.

Physics and Instantaneous Performance of Radial Turbines in Unsteady Flows: Validity of the Quasi-Steady Assumption for the Rotor

Abstract Radial turbines are frequently submitted to unsteady inlet flows, for example, in turbocharging applications. Complex flows dominated by waves propagation take place, and advanced methodologies are required. Such complexity is hardly compatible with industrial constraints and design time scales. Also, the validity of the usual performance indicators, such as efficiency, is questionable in unsteady flows. However, the need for simplification led the community to develop modeling strategies for unsteady effects, based on hypotheses. One of those is that the rotor flow is assumed quasi-steady. This assumption is assessed by different criteria of the literature. It also enables an adaptation of performance indicators such as efficiency and pressure ratio. But the validity of such an assumption is still under discussion. The present paper is a contribution to this discussion. It focuses on a physical analysis of the physics involved in unsteady flows and the consequences that it produces on the instantaneous performance. Unsteady numerical simulations are analyzed, performed on a realistic radial turbine stage, which was submitted to different transient phases. An instantaneous overshoot of the turbine torque is observed for some transient regimes. Such a result demonstrates that the rotor flow is not immune to unsteady effects. A discussion is then conducted around the possible validity of the quasi-steady assumption for the rotor. This discussion includes the different criteria already found in the literature, and the alternative formulation proposed in this contribution, based on the ratio of time scales.

Performance evaluation on radial turbines with potential working fluids for space closed Brayton cycle

The performance of radial turbines with the He-Xe mixtures, helium, argon and air are examined in this paper. The published approach pertaining to Chapman-Enskog kinetic theory and corresponding states theory is adopted to calculate the transport properties of He-Xe mixtures with two different molecular weights of 15.9 g/mol and 40 g/mol. The independent or combined effects of the flow Euler number (Eu), Reynolds number (Re) and inflow velocity on flow similarity are discussed based on flat-plate flow. Under the consistent above conditions, the flows of these fluids are similar and the flow loss is merely a function of fluids properties. The established flow similarity conditions form a procedure to calculate the boundary conditions of similar turbines and its application makes the flow similar in radial turbines passages. It is reflected in the consistent topology skeleton of flow structures and the identical parameter distributions in the flow section. The turbines with He-Xe mixtures, Ar and air shares a pretty similar tendency of efficiency line and the values differ little. The differences between these turbines under the same working point have an upper limit of 0.3% before critical state. At the design point, a similar velocity triangle instead of an identical one can guarantee the flow similarity and an approximate efficiency compared with others. Once the working condition deviates from the design point, the efficiency error between the helium and other fluids widens as the working condition deviation increases.

Design and off-design optimisation of an organic Rankine cycle (ORC) system with an integrated radial turbine model

This paper investigates the design and thermodynamic optimisation of both sub- and transcritical organic Rankine cycle (ORC) power systems featuring radial turbines via performance calculations using mean-line models. The emphasis is on rapid performance predictions for a given turbine geometry, as well as geometric optimisation for a given heat source. From three specified quantities, which are the turbine inlet temperature, inlet pressure and mass flow rate, the other flow properties (e.g., outlet pressure and temperature) are computed, together with derived quantities which are required for cycle- or system-level assessments, such as the isentropic efficiency of the turbine. Experimental investigations from the open literature suitable for validation purposes are summarised and analysed with respect to their strengths and weaknesses. Similar computational fluid dynamic (CFD) simulations are also used to complement the available experimental data. The main contributions of this paper are that it provides a comprehensive overview of radial turbine performance modelling, and that it proposes a detailed framework that can be used for the improved development of efficient thermodynamic power systems based on a unified mean-line model that is validated against experimental data and supported by CFD results. Specifically, predictions from the mean-line model show good accuracy over a wide range of operating conditions for different turbine designs and fluids with compressibility factors from 0.6 to 1.0. Finally, in order to demonstrate its efficacy, the integrated radial turbine and ORC system design framework is used in a case study of a nominally 400-kW power system with propane as the working fluid in low-grade waste-heat application, where the turbine inlet temperature is fixed at 150 °C and the condenser temperature is fixed at 15 °C. The novelty of this work arises from the optimisation of the turbine nozzle vane position at off-design conditions. This feature, along with multi-stage radial turbine designs are shown to allow high-performance operation over a wide range of off-design conditions. Specifically, good efficiencies are demonstrated over a wide range of heat-source fluid flow rates when employing an adjustable nozzle geometry, as is the ability of radial turbines to achieve efficiencies that are not constrained by the pressure ratio across them by replacing single-stage designs with multi-stage designs.

Radial Turbine Performance Prediction and Design Optimization Whit Matlab Tool

Radial Turbine Performance Prediction and Design Optimization Whit Matlab Tool

Experimental study of organic Rankine cycle system and expander performance for heavy-duty diesel engine

A small scale organic Rankine cycle system capable of generating electric power using exhaust gas of a 7.25 ℓ heavy duty diesel engine was built and tested. A custom-designed radial inflow turbine was used as an expansion machine, and NOVEC649 was used as the working fluid. In order to maintain steady state operation, a thermal oil loop was installed in the system as an intermediate circuit between the exhaust gas and organic Rankine cycle loop. Compared to the previous study by the authors, the operating conditions were further extended. In addition, the effects of cooling water temperature and working fluid superheating temperature on turbine performance were explored in the current study. The coupled engine-organic Rankine cycle system presented an electrical power, turbine efficiency and thermal efficiency of 9 kW, 35% and 4%, respectively. The results showed that both cooling water temperature and working fluid superheating temperature had a negative impact on the radial turbine performance (generated power and efficiency). The average decrement of the generated power and turbine efficiency were 2.4% and 1.7%, respectively, when increasing the cooling water temperature by 2 °C, and 2.5% and 7.3% when increasing the working fluid superheating temperature by 2 °C. Moreover, the extended tests were beneficiary for validating the proposed performance prediction meanline model developed by the authors in a previous study. The maximum deviation between the measured and predicted turbine efficiency was 3.5%.

Preliminary Design of Multistage Radial Turbines Based on Rotor Loss Characteristics under Variable Operating Conditions

The loading-to-flow diagram is a widely used classical method for the preliminary design of radial turbines. This study improves this method to optimize the design of radial turbines in the early design phase under variable operating conditions. The guide vane outlet flow angle is a key factor affecting the off-design performance of the radial turbine. To optimize the off-design performance of radial turbines in the early design phase, we propose a hypothesis that uses the ratio of the mean velocity of the fluid relative to the rotor passage with respect to the circumferential velocity of the rotor as an indicator to indirectly and qualitatively estimate the rotor loss, as it plays a key role in the off-design efficiency. Theoretical analysis of rotor loss characteristics under different types of variable operating conditions shows that a smaller design value of guide vane outlet flow angle results in a better off-design performance in the case of a reduced mass flow. In contrast, radial turbines with a larger design value of guide vane outlet flow angle can obtain a better off-design performance with increased mass flow. The above findings were validated with a mean-line model method. Furthermore, this study discusses the optimization of the design value of guide vane outlet flow angle based on the matching of rotor loss characteristics with specified variable operating conditions. It provides important guidance for the design optimization of multistage radial turbines with variable operating conditions in compressed air energy storage (CAES) systems.

Impact of the wastegate opening on radial turbine performance under steady and pulsating flow conditions

The present article attempts to describe the behavior of wastegated turbines under various steady and pulsating flow conditions. For this, meanline and one-dimensional numerical codes including appropriate modeling approaches for wastegated turbines have been developed with the FORTRAN language. These codes were validated against experiments with an established test rig at the National School of Engineers of Sfax. The discharge coefficient map of the wastegate was determined with a developed correlation built from experiments, and it was served as an input to the developed codes for interpolations during computation. This correlation is based on a two-dimensional non-linear dose-response fitting relationship instead of classical polynomial function which is one novelty of the article in addition to the one-dimensional modeling methodology. The normalized root mean square error (NRMSE) of both cycle-averaged efficiency and mass flow parameter (MFP) remains below 2% which confirms the validity of the proposed calculation approach. The results indicated a large deviation in the turbine performance under pulsating flow conditions compared to the steady state ones. The shape of the hysteresis loop of the turbine efficiency remains unchanged toward the variation of the wastegate valve angle at the same pulse frequency. The mass flow hystereses loop area is decreased by around 50% as the pulse frequency increases from 33 up to 133.33 Hz. An increase of less than 1% of the cycle-averaged efficiency has been reported when the bypass flow through the wastegate increases. The fluctuation of the efficiency is decreased by 1.5% when the wastegate valve becomes fully opened under the whole range of the pulse frequency.

Flow analysis and performance improvement of a radial inflow turbine with back cavity under variable operation condition of compressed air energy storage

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.

Investigation of Radial Turbine performance of Automotive Turbocharger under Pulsating flow

Investigation of Radial Turbine performance of Automotive Turbocharger under Pulsating flow

Effects of different working fluids on the performance of a radial turbine in an organic Rankine cycle power system

Organic Rankine cycle (ORC) power systems are widely used for low-temperature heat recovery. The radial turbine is the most important component in the ORC system and its performance is significantly dependent on the working fluid. Therefore, the effect of different working fluid on the performance of radial turbine in ORC system for the low-temperature heat source (120~180 °C) was investigated. First, the feasibilities of different working fluids for 150 kW radial turbine using R600a as designed working fluid were investigated. The thermal aerodynamic calculation of R600a at design condition was conducted with evaporation temperature 95 °C and condensation temperature 38 °C. The operation parameters of 5 non-designed working fluids (R600, R245fa, R245ca, R123 and R601a) were selected in the same temperature variation range as R600a. Then, the performance of a radial turbine for six working fluids at design condition was analyzed, and their three-dimensional flow field performances were also obtained by CFD numerical simulation. Finally, to broaden the operation range of the radial turbine and investigate the matching relationship between operation parameters and different working fluids, the off-design performances of radial turbine using six working fluids were analyzed and the effect of rotation speed, inlet pressure and inlet temperature on the performance of radial turbine was obtained. Results show that the performance of the radial turbine using the designed working fluid R600a is the best with efficiency of 82.7 % and output power of 150.5 kW. For the non-designed working fluids, the comprehensive performance of R600 was also judged to be good owing to the highest efficiency (85.1 %) and a relatively high power output (115.8 kW) among the fluids tested. For other working fluids, the output power of the radial turbine decreased obviously. There exists an optimum rotation speed for different working fluids to ensure that the radial turbine has the highest efficiency. The inlet pressure has a larger effect on the performance of the radial turbine than that of the inlet temperature. The results can provide basic data for the optimization design and operation of radial turbines in the ORC system.

내연기관에 적용하기 위한 10 kW급 유기랭킨사이클의 구심 터빈에 관한 실험적 연구

내연기관에 적용하기 위한 10 kW급 유기랭킨사이클의 구심 터빈에 관한 실험적 연구

Numerical Prediction of a Radial Turbine Performance designed for Automotive Engines Turbocharger

These days the turbocharging system is assuming an essential part in enhancing car engines performance and diminishing fuel utilization and the fumes emanations, in spark-ignition and compression ignition engines. The performance of a radial turbine for the turbocharger device is heavily affected by the flow dynamics in a radial impeller. Furthermore, modification and improvement of a radial turbine impeller is a challenging task for turbomachinery engineers. Hence, this study aimed to further computational fluid dynamic analyses of a radial turbine stage performance .The design characteristics of a radial turbine stage, was used to simulate the flow by using independent packages of ANSYS CFX. The comparative study of a three dimensional flow simulation will give a more reasonable results of the turbine stage flow behavior and computational fluid dynamic simulation can give a more detailed result and reveal unexpected flow behavior like separation and vortexes.The results showed that the fluid flow dynamics within a turbine stage has indicated a noticeable performance characteristics. Obviously, it was observed that the pressure ratio and volume flow rate and efficiency were predicted numerically. Overall numerical results obtained from computational fluid dynamic simulations could produce a highly reliable for estimation on the performance a radial turbine of turbocharger.

Numerical Sensitivity Analysis for Supercritical CO2 Radial Turbine Performance and Flow Field

The predominant advantage of a supercritical CO2 (SCO2) Brayton cycle is it’s diminished compression work when compared to an ideal working fluid such as helium, due to low compressibility factor. For flows where the density approaches the critical density, molecular interactions get stronger and the ideal gas assumption is no longer appropriate.As a means to investigate the accuracy of real gas models and sensitivity of the performance of a turbomachine on the numerical accuracy in the supercritical region, numerous unsteady simulations of a radial turbine have been performed. Real Gas Properties (RGP) table has been generated to overcome difficulties of instabilities in simulations in the supercritical region. Four Equation of States (EOS) models with different RGP table resolutions have been studied and results are compared with the experimental measurement performed at the Sandia National Laboratory. The studied unshrouded radial impeller has 11 blades while the nozzle has 10 vanes. The unsteady simulation results show the dependency of the predicted radial turbine performance on the RGP table resolution as well as on the implemented EOS models. In general, the results indicate that by using appropriate EOS model and a look up table with high resolution, the CFD can predict turbine performance with high accuracy while the use of some EOS and low resolution look up tables lead to significant deviations between the simulated and measured results. As a result of this study, an appropriate EOS model and sufficient resolution of the look-up table for turbines operating at supercritical region are suggested.

Effect of end-wall riblets on radial turbine performance

This paper presents a detailed study of the impact of manufacturing residual riblets at the rotor hub surface of a radial inflow turbine on the flow within the rotor passages and their contribution to drag reduction. Numerical analysis has been used to study the effects of those features at design point conditions. Riblets with different height and spacing have been examined to determine the riblet geometry where the maximum drag reduction is achieved. The relative height of the riblets to rotor inlet blade height was introduced to generalise the results. At the end of this study the results were compared with the available data in literature. It was found that the introduction of riblets could reduce the wall shear stress at the hub surface, while they contribute to increasing the streamwise vorticity within the rotor passage. For the geometries tested, the minimum drag was achieved using riblets with relative height hrel = 2.5% equivalent to 19.3 wall units. The results revealed that the spacing between riblets have a minor effect on their performance, this is due to the size of the streamwise vortex above the hub surface which will be discussed in this work.

Radial turbine performance measurement under extreme off-design conditions

During automotive urban driving conditions and future homologation cycles, automotive radial turbines experience transient conditions, whereby the same operate at very high blade speed ratios and, thus, at very low power outputs. Under those conditions, the turbine power output might not be enough to feed the mechanical power needs of the compressor. Typical fast one-dimensional full engine simulations rely on steady-state performance maps to characterize the turbocharger. Due to the restricting compressor braking power, extreme off-design measurements cannot be obtained in standard gas stands without using an external brake instead of the compressor or without using a motor attached to the turbocharger shaft. Such turbocharger assemblies cause shaft balancing issues inherent to the connection to a brake operating at high rotational speeds or need basic changes of the turbocharger geometry. This paper presents a novel approach for turbine performance map measurements at very low expansion ratio and very low mass flow without the aforementioned issues. The method uses the turbocharger compressor as a centrifugal turbine, providing mechanical power to the shaft and enabling turbine performance measurements from points of very high expansion ratio up to very low pressure ratio. It is even possible to measure at almost zero flow rate in the turbine when it consumes shaft power instead of producing it. This experimental procedure that can be applied to whatever turbocharger produces valuable information for the development and validation of turbine performance models aiming to extrapolate its behaviour at off-design conditions.

Similarity Theory Based Radial Turbine Performance and Loss Mechanism Comparison between R245fa and Air for Heavy-Duty Diesel Engine Organic Rankine Cycles

Organic Rankine Cycles using radial turbines as expanders are considered as one of the most efficient technologies to convert heavy-duty diesel engine waste heat into useful work. Turbine similarity design based on the existing air turbine profiles is time saving. Due to totally different thermodynamic properties between organic fluids and air, its influence on turbine performance and loss mechanisms need to be analyzed. This paper numerically simulated a radial turbine under similar conditions between R245fa and air, and compared the differences of the turbine performance and loss mechanisms. Larger specific heat ratio of air leads to air turbine operating at higher pressure ratios. As R245fa gas constant is only about one-fifth of air gas constant, reduced rotating speeds of R245fa turbine are only 0.4-fold of those of air turbine, and reduced mass flow rates are about twice of those of air turbine. When using R245fa as working fluid, the nozzle shock wave losses decrease but rotor suction surface separation vortex losses increase, and eventually leads that isentropic efficiencies of R245fa turbine in the commonly used velocity ratio range from 0.5 to 0.9 are 3%–4% lower than those of air turbine.