Radial Turbine Research Articles

Performance assessments and simulations of ROT (radial outflow turbine) for back-pressure turbine generator system

The high pressure steam is regulated by the Pressure-Reducing Valves (PRVs) to suit the various industrial process; however, this, inevitably leads to economic and energy losses. In this study, PRV is replaced by a back-pressure turbine generator comprising a Radial Outflow Turbine (ROT). The structural characteristics of the ROT, such as the easy adjustment of the tip clearance, make it possible to control the steam properties. The steam with selectively reduced pressure (and temperature) can be provided to users. The blade geometry of the ROT is designed using a commercial software. The numerical prediction of the fluid properties is carried out using a real fluid model in ANSYS-CFX. The simulation results are compared with the experimental results obtained under the same off-design conditions. The tip clearance (100, 300 and 500μm) are applied as a parameter to investigate the change of performance and to adjust the properties of the discharged steam. The experimental results show that the maximum electrical power produced at the minimum tip clearance is 12.8 kW, and the temperature and pressure differences tend to decrease with increasing tip clearance. These results demonstrate the potential of the ROT as a PRV and energy recovery device in back-pressure turbines.

Twin-entry turbine losses: An analysis using CFD data

The current paper presents a computational fluid dynamics (CFD) flow behaviour and losses analysis of twin-entry radial turbines in terms of its Mass Flow Ratio ( MFR, the ratio between the flow passing through one of its intake ports and its total mass flow), focusing on the mixing phenomena in the unequal admission conditions cases. The CFD simulations are first validated with experimental data. Then, the losses mechanisms are analysed and quantified in the different parts of the twin-entry turbine in terms of the MFR value. A sudden expansion is found at the junction of both branches in the interspace between volutes and rotor for unequal and partial admission cases. Tracking the flow coming from each of the turbine intake ports, it has been observed that both flow branches do not fully mix with each other within the rotor. Another source of losses has been identified in the contact between both flow branches due to their momentum exchange that depends on the difference between both flow branches velocities. These losses have not been considered before, and they should be included in mean line loss-based models for twin-entry turbine since they are very significant for unequal admission conditions.

Investigation of unsteady flow in the unscalloped radial turbine cavity

This paper presents an unsteady numerical study of the unsteady flow in the unscalloped radial turbine cavity considering the effect of computational sector size and sealing flow rate. A simplified U-shaped cavity with vanes and blades was simulated and the sealing efficiency was obtained using additional variables method. Unsteady low-pressure structures exist under a certain sealing flow rate, which is similar with axial turbine cavity, while the impact area is much larger. A comparison of computational domains sizes for 60° and 360° shows that whether the sector model can accurately predict the flow field depends highly on the number of low-pressure structures. As the sealing flow rate increases, the number and the speed of low-pressure structures at high radius decrease, and the corresponding low-frequency amplitude increases initially but decreases subsequently. The speed of low-pressure structure is positively correlated with its number, which seems contrary to the phenomenon observed in the axial turbine cavity.

Part-load performance prediction model for supercritical CO2 radial inflow turbines

There is recent focus on supercritical CO2 (s-CO2) Brayton power cycles as the next-generation thermal energy conversion choice. They are efficient, compact, economic, and environmentally friendly. They are also scalable without efficiency penalties and suitable for small and large sizes. The most critical component is reported to be the turbine. A turbine design should achieve good performance at its design operating conditions and maintain acceptable performance at off-design conditions. Off-design operating conditions are relevant because thermal power plants are increasingly required to meet varying electricity demand in continuously changing environments. This paper presents a novel one-dimensional part-load performance prediction model for s-CO2 turbines. The novelty of the present model comes from the accurate prediction of the part-load s-CO2 turbine performance with less than 10% deviation, validated against reliable three-dimensional computational fluid dynamics simulation. Furthermore, the proposed model uses fundamental fluid dynamic equations and a real gas property library and does not require calibration. A Python code based on the proposed model can generate a full list of essential performance variables and internal flow information.

A Comparison of Partial Admission Axial and Radial Inflow Turbines for Underwater Vehicles

The metal fueled steam Rankine cycle has been successfully applied to Unmanned Underwater Vehicles. However, the suitable turbine configuration is yet to be determined for this particular application. In this paper, the mean-line design approach based on the existing empirical correlations is first described. The corresponding partial admission axial and radial inflow turbines are then preliminarily designed. To assess the performance of designed turbines, the three-dimensional Computational Fluid Dynamics (CFD) simulations and steady-state structural analysis are performed. The results show that axial turbines are more compact than radial inflow turbines at the same output power. In addition, since radial inflow turbines can reduce the exit energy loss, this benefit substantially offsets the increment of the rotor losses created by the low speed ratios and supersonic rotor inlet velocity. On the contrary, due to the large volume of dead gas and strong transient effects caused by the high rotor blade length of radial inflow turbines, the overall performance between axial and radial inflow turbines is comparable (within 4%). However, the strength of radial inflow turbines is slightly superior because of lower blade inlet height and outlet hub radius. This paper confirms that the axial turbine is the optimal configuration for underwater vehicles in terms of size, aerodynamics and structural performance.

Three-Dimensional Performance Analysis of a Radial-Inflow Turbine for Ocean Thermal Energy Conversion System

Turbine is one of the key components of the ocean thermal energy conversion system (OTEC), and its aerodynamic performance and geometric dimension affect the performance of the system directly. This paper proposes a design method for the radial inflow turbine suitable for the ocean thermal energy conversion based on the parameter optimization of the ocean thermal energy conversion system. Aiming at the application characteristics of marine thermal energy conversion in a small temperature difference environment and the special thermophysical properties of the organic working fluid in this environment, one-dimensional design and three-dimensional CFD analysis of the turbine is separately done, of which the results were compared. At the same time, the performance of the turbine was verified by changing the inlet and outlet conditions of the radial turbine under the design conditions. The conclusion is that the three-dimensional CFD results of the turbine are in good agreement with the one-dimensional design, and the internal flow field of the turbine is stable, without obvious backflow and eddy current, which meets the application requirements of the ocean thermal energy conversion.

Using a CFD analysis of the flow capacity in a twin-entry turbine to develop a simplified physics-based model

The current paper presents a flow behaviour analysis of twin-entry radial turbines by means of experimental measurements and computational fluid dynamics (CFD) simulations. The experimental data were measured at partial, unequal and full admission conditions, and was used to globally validate CFD simulations. The experimental results hinted towards considering twin-entry turbines as two separated single-entry turbines working in parallel when used in simplified physics-based models such as in one-dimensional simulations. After analysing the CFD results, a simple flow capacity model was developed, exploiting some of the observed characteristic phenomena to reduce the number of fitting parameters to their minimum while keeping its accuracy and extrapolation capabilities.

The impact of volute aspect ratio and tilt on the performance of a mixed flow turbine

Current trends in the automotive industry towards engine downsizing means turbocharging now plays a vital role in engine performance. The purpose of turbocharging is to increase the engine inlet air density by utilising, the otherwise wasted energy in the exhaust gas. This energy extraction is commonly accomplished through the use of a radial turbine. Although less commonly used, mixed flow turbines can offer aerodynamic advantages due to the manipulation of blade leading (LE) angles, improving performance at low velocity ratios. The current paper investigates the performance of a mixed flow turbine with four volute designs, two radial and two tilted volutes each with one variant with an aspect ratio (AR)=0.5 and one with AR = 2. To ensure constant mass flow parameter (MFP) for aerodynamic similarity, volute area to radius ratio (A/r) was manipulated between the design variants. The maximum variation of cycle averaged normalized efficiency measured between the designs was 2.87%. Purely in the rotor region, the variation in normalized cycle averaged efficiency was 3%. The smallest volute AR designs showed substantial secondary flow development. The introduction of volute tilt further complicated the secondary flow development with the introduction of asymmetry to the flows. It was established that both AR and tilt have a notable effect on secondary flows, rotor inlet conditions and over all mixed flow turbine performance.

Coupling optimization of casing groove and blade profile for a radial turbine

In order to suppress the tip leakage loss and increase the isentropic efficiency in a radial turbine with low aspect ratio blade, a new coupling flow control technology including casing groove and NACA blade profile is proposed and optimized numerically. The coupling effects of casing groove size LS, groove number Numslot, maximum thickness location of profile MLT and leading parameter of profile LP on isentropic efficiency of a radial turbine are obtained with Design of Experiment (DOE) and response surface model. A genetic optimization is achieved and the coupling flow control mechanism is revealed. Complex variation of isentropic efficiency is observed with the coupling effect of groove size and groove number, and maximum isentropic efficiency variation of 0.6% is obtained with the increase of LS when Numslot is 3. The coupling effect between LS and LP, is also significantly influenced by groove number. The lower limit of LP for maximum isentropic efficiency is decreased from 7 to 3 with the increase of groove number. The optimization result illustrates that the isentropic efficiency can be increased by 0.9% at design point when the LS, Numslot, MLT and LP are 0.8 mm, 2, 0.1, and 0.8 respectively. A maximum isentropic efficiency increment of 2.0% is also found when total pressure ratio is 2.1. The optimal casing groove forms a flow opposite to the tip leakage flow to suppress the impact range of the secondary flow near suction surface. At the same time, the optimal NACA profile also decreases the tip leakage velocity near trailing, suppresses the tip leakage vortex generation, and reduces the trailing edge loss.

Evaluation of the maturity level of biomass electricity generation technologies using the technology readiness level criteria

This article assesses the level of maturity of current biomass power generation technologies, by using metrics of technology readiness levels. A questionnaire was developed and sent to hundreds of bioenergy experts from several countries. A total of 101 answers to the survey were received from the experts. Such analysis was based on a method commonly used in the defense sector, but modified, mainly in terms and concepts issues, about particularities of biomass energy generation technologies. Obtained results indicate that 62.07% of experts in the sector consider Conventional Rankine Cycle technology having already a high degree of maturity, with a Technology Readiness Levels of 8 or higher, and 37.11% of experts consider Organic Rankine Cycle technology also has a high degree of maturity. Technology Readiness Level definition for Gasifier/Internal combustion engine technology resulted to be a complex task as reflected in the present survey’s results, where the weighted Technology Readiness Level is 6. The technologies showing lower weighted TRL values are integrated gasifier combined cycle, externally fired gas turbines, steam radial turbines, screw expander, gasifier/gas microturbine, and Stirling engines. Survey results and reviewed performance data provide very useful information for preliminary technology selection in biomass electricity generation projects.

Investigation on Interaction between Geometry and Performance and Design of S-CO2 Radial Inflow Turbine’ s Vaneless Inlet Volute

The inlet volute is one of the key components that guide the working fluid into the radial inflow turbine. It has a significant effect on the performance of the radial inflow turbine. The conventional design criteria for the vaneless inlet volute mainly focuses on the ideal gas, which does not apply to real gas cases, such as supercritical carbon dioxide(S-CO2). In this paper, an MW-class S-CO2 radial inflow turbine is studied. Firstly, the inlet volute design of the radial inflow turbine with a vaned stator is completed, and the flow in the whole machine is calculated using CFD simulations. Then, based on the inlet boundary conditions of the impellers, the vaneless inlet volute with different throat areas and cross-sectional area distributions are investigated. The results indicate that the size of the counter rotating vortexes in the vaneless inlet volute increases with the throat area increasing, and is also influenced apparently by the cross-sectional area distribution. The volute throat area has little effect on the circumferential distribution of the outlet airflow angle but changes the average value of the airflow angle. The cross-sectional area distribution of the volute influences the circumferential distribution of the outlet flow angle. The result indicates that volute with a small-scale convex profile has a uniform outlet flow field. Compared to the turbine with the vaned stator, the radial dimension of the vaneless volute turbine obtained in the final design is significantly reduced, and the total-total efficiency at the design point is 85.62%, which meets the design requirements. Moreover, it also has good performance at off-design operating conditions.

Modeling and parametric optimization for a solar-powered closed-cycle micro gas turbine for space applications

The research describes the theory design and the modeling of a closed cycle micro gas turbine power plant (CMGTP). A computer simulation model in ASTRA is used to model specifically for this cycle. The software model has been tested for various configurations of gas turbines. For the commercial viability and success of the CMGTP, it should have significant operational feasibility. The working fluid properties play a vital role. The research is a feasibility study to examine the technology for Brayton-cycle based solar thermal power plants and to optimize the model in comparison with Solar array photovoltaic cells to increase the power density by increasing the power generated per unit solar-collector area. A mathematical model for CMGTP was de-signed to power satellites in space environments. The goal is to provide electricity from a parabolic mirror acting as a heat source that is collected by pointing at the sun. The Closed Brayton Cycle power was simulated to produce an output of 6 kW at the generator terminal. The heat source generated from the sun was considered to be around 750 K to 1250 K. The vacuum at the space radiation environment was considered to be 200 K acting as a coolant sink. The optimization of the power plant priorities is followed as High thermal-to-electric efficiency, Low mass, and volume. Computer simulation for thermodynamic analysis was performed on the selection of the working fluids, Brayton cycle design parameters, a heat exchanger (heating and cooling temperatures) that meets the best criteria. A system-level tradeoff study was performed to optimize for achieving target functions for critical factors. The CMGTP consists of a centrifugal compressor, a radial in-flow turbine on a single shaft powering a two-pole permanent magnet alternator.

Performance and Losses Analysis for Radial Turbine Featuring a Multi-Channel Casing Design

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

Radial Turbine Design for Solar Chimney Power Plants

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.

Effects of working fluid type on powertrain performance and turbine design using experimental data of a 7.25ℓ heavy-duty diesel engine

This paper outlines a comparative assessment of the effects of various fluid types on the performance of powertrain performance (i.e. heavy-duty diesel engine + organic Rankine cycle) and the design of the radial inflow turbine. The considered organic fluids are R123 (dry), R21 (wet) and R141b (isentropic). The exhaust gas of a 7.25ℓ heavy duty diesel engine is utilized as the system heat source. The powertrain system, including the radial inflow turbine, is analyzed under superheated conditions and near saturated vapor curve, at various operating conditions. Surprisingly, wet fluids offer attractive cycle performance in the superheated region (12.65% on average) followed by isentropic fluids (12% on average). Near the saturated vapor curve, isentropic fluids are found to present best cycle performance (13.77% on average) while wet fluids offer the lowest (10.90% on average). However, wet fluids present a compact turbine design and best isentropic efficiency with an average value of 82% in the superheated region. Near the saturated vapor curve, isentropic and dry fluids offer relatively lower turbine efficiencies (80.9% and 80.3 on average) while wet fluids result in two-phase condition at the turbine exit which results in poor turbine performance (63.30% on average). Moreover, R141b shows best improvements of engine power and BSFC with values of 11.18% and 10%, respectively, at 1 kg/s. Compared to R123 and R141b, R21 improved the engine power and BSFC by at least 7.86% and 7.63% under superheated conditions.

Turbine optimization potential to improve automotive Rankine cycle performance

Waste heat recovery (WHR) systems based on organic Rankine cycle (ORC) are gaining increasing interests for reducing the exhaust emissions and fuel consumption of heavy-duty diesel engines. The expansion machine (i.e. radial inflow turbine) is a critical component of the ORC system and its performance substantially influences the overall powertrain performance. Therefore, this study presents an effective methodology that combines the previously developed mean-line design model, a 3D CFD analysis and a multi-objective optimization technique for a high pressure-ratio radial turbine. The exhaust gases of a 7.25ℓ heavy-duty diesel engine is used as the heat source with NOVEC 649 as the cycle working fluid. The optimized radial turbine is then integrated with the powertrain system to explore its effects on engine power, BSFC and cycle efficiency, at both design and off-design conditions. The ORC improved engine power and BSFC by maximum values of 5.7% and 5.4%, respectively, with the baseline turbine. With the optimized turbine, the power and BSFC improvements reached 6.15 and 5.8%, respectively. Compared to the baseline turbine, the optimized turbine isentropic efficiency increased by 10.68% at nominal conditions. As a result, the cycle thermal efficiency was significantly improved presenting 8.2% higher efficiency compared to the cycle with baseline turbine. The combination methodology has proven effective as it significantly improved the powertrain performance.

Aerodynamic design and computational fluid dynamic analysis of radial outflow turbines for steam Rankine cycle and supercritical carbon dioxide Brayton cycle

The first part of this paper presents the design of a radial outflow steam turbine for a micro steam power pump block of 200 kW capacity based on a unique Ljungstrom turbine design methodology. Computational fluid dynamic (CFD) simulations were carried out for the 18-stage radial outflow steam turbine at design and off-design points, and results proved the validity of the undertaken design methodology. The design point CFD simulation showed a total to total efficiency of 74.4% for the steam turbine. Specific speed and specific diameter values for the radial outflow steam turbine stages were calculated and superimposed on the Balje's specific speed-specific diameter chart, thus identifying a unique radial outflow turbine zone in the chart. The second part of this paper presents a new design methodology based on specific speed and specific diameter values for designing a supercritical carbon dioxide radial outflow turbine for a 1 MW supercritical carbon dioxide (SCO2) Brayton cycle. CFD simulations were carried out at design and off-design points for the SCO2 turbine. The total to total efficiency from the CFD simulation at the design point for the SCO2 turbine is 84.6%.

Aerodynamic design and computational fluid dynamic analysis of radial outflow turbines for steam Rankine cycle and supercritical carbon dioxide Brayton cycle

The first part of this paper presents the design of a radial outflow steam turbine for a micro steam power pump block of 200 kW capacity based on a unique Ljungstrom turbine design methodology. Computational fluid dynamic (CFD) simulations were carried out for the 18-stage radial outflow steam turbine at design and off-design points, and results proved the validity of the undertaken design methodology. The design point CFD simulation showed a total to total efficiency of 74.4% for the steam turbine. Specific speed and specific diameter values for the radial outflow steam turbine stages were calculated and superimposed on the Balje's specific speed-specific diameter chart, thus identifying a unique radial outflow turbine zone in the chart. The second part of this paper presents a new design methodology based on specific speed and specific diameter values for designing a supercritical carbon dioxide radial outflow turbine for a 1 MW supercritical carbon dioxide (SCO2) Brayton cycle. CFD simulations were carried out at design and off-design points for the SCO2 turbine. The total to total efficiency from the CFD simulation at the design point for the SCO2 turbine is 84.6%.

An engineering approach for the fast simulation of radial inflow turbines with vaneless spiral casing by single-channel CFD models

The basic RANS-CFD analysis of the simplest radial-inflow turbine configuration is the subject of this paper. An original technique is here proposed to model the effect of the vaneless spiral casing using single-channel CFD calculations and providing an effective alternative to the more complex simulation of the 360-degree domain otherwise required to simulate this turbine configuration. The aim of the paper is to verify the effectiveness of the proposed modelling technique as a reliable engineering approach conceived to support the preliminary design phase of radial-inflow turbines with time-effective CFD calculations. To this end, the open-source CFD code MULTALL has been used to predict the aerodynamic performance of optimal designs of radial-inflow turbines with different specific speed and diameter and working with air as ideal gas. The MULTALL predictions are compared with the corresponding steady-state results obtained by calculations suited to the preliminary assessment of radial turbines designs performed on fully 360-degree turbine domains using the commercial code Star CCM+®. The investigation is conducted on two turbines that are designed in accordance with a widely validated method. The results show that the proposed CFD approach predicts well the trends and values of the aerodynamic performance of both the turbine designs: a 5% overestimation of the performance predicted by the fully 360-degree CFD models was never exceeded. The suggested turbine modelling approach implemented in MULTALL requires a three times lower computation time than the corresponding traditional 360-degree model.

Supercritical carbon dioxide turbomachinery development using scaling methodology, computational fluid dynamics and experimental testing in aeroloop

Supercritical carbon dioxide (SCO2) turbomachinery design experience is limited. This paper examines similarity-based scaling strategy to develop a radial inflow turbine and a centrifugal compressor from existing proven designs for a 50 kWe SCO2 Brayton cycle. The SCO2 turbine and compressor are developed from well-established NASA 1730 air turbine and NASA 4613 radial pump, respectively. Computational fluid dynamic (CFD) simulations with air and SCO2 and experimental testing in aeroloop are carried out for the developed turbomachinery. The results are compared with original NASA test data. For the turbine, the CFD simulation and experimental results were in good agreement with NASA data. For the compressor, CFD simulation results with SCO2 showed good conformance especially the efficiency values, which were much lower for air. The compressor experimental results were well away from the NASA data when head rise coefficient was considered, but the flow coefficient zone coincided with that of simulation.