Radial Outflow Turbine Research Articles

A comprehensive preliminary design methodology and an optimization workflow for single-stage radial-outflow turbines and application for 10 MW sCO2 turbines

Development of efficient turbines for sCO2 power cycles is crucial to increase the efficiency, economic feasibility, and competitiveness of future thermal power plants. Radial-outflow turbines are recently considered as a viable power block option for sCO2 power cycles for several applications. This research aims at presenting a detailed and replicable design procedure for radial-outflow turbines. A detailed one-dimensional design method was first developed and validated, then an optimization design workflow was developed using this one-dimensional design method. Utilizing this workflow, the impact of some key design parameters on turbine performance was studied. It was found that the velocity ratio, specific speed, and flow coefficient have significant impact on turbine performance, the reaction degree has moderate impact, and the diameter ratio has the lowest impact. The criterion of selecting the design variables was given and its applicability to different boundary conditions and constraints has also been illustrated. Furthermore, a test case turbine of 10 MW power scale was designed using the developed method, and 3D CFD simulations were performed to study the on-design and off-design performance of the designed turbine. Results show that high efficiency (above 90.0 %) and overall good off-design performance can be obtained from sCO2 radial-outflow turbines in the 10 MW power scale using the developed design methodology when the design parameters are properly selected. The developed 1D design and optimization method is directly applicable to other working fluids and can be easily extended to design multistage radial-outflow turbines.

A Review on the Preliminary Design of Axial and Radial Turbines for Small-Scale Organic Rankine Cycle

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.

Numerical investigation and performance enhancement of an ammonia-water radial-outflow turbine through the flow-oriented optimization

The radial-outflow turbine has advantages due to its liquid-rich gas adaptability when applied in a Kalina ammonia-water cycle system for the utilization of geothermal energy and waste heat. However, the existing radial-outflow turbine shows relatively lower efficiency than the conventional radial-inflow turbines due to its distinct stage configuration and the lack of efficient design method. In the present study, numerical investigation has been conducted on a radial-outflow turbine adopted in Kalina cycle system, by which the turbine flow losses are analyzed. To enhance the turbine performance, a design optimization method has been developed, which includes the following features: the flexible geometry variations are realized to explore the optimization potentials, where the stator and rotor blades are optimized simultaneously; the flow-oriented objective function is established to drive the optimizer to suppress the flow losses in blade passages while adjust the flow matching. To solve the complex geometry optimization problem, adaptive optimization algorithm is imported to accelerate global searching and reduce the costly Computational Fluid Dynamics evaluations. The developed optimization method has been applied in the geometry optimization of a radial-outflow ammonia-water turbine. Benefitting from the fine-tuned blade geometries, the flow matching between stator and rotor is adjusted and the flow losses are mitigated. Thus, the turbine efficiency and shaft power are improved by 6.46% and 5.85%, respectively.

Multipoint Design Optimization of a Radial-Outflow Turbine for Kalina Cycle System Considering Flexible Operating Conditions and Variable Ammonia-Water Mass Fraction

The radial-outflow turbine has advantages due to its liquid-rich gas adaptability when applied in the Kalina ammonia-water cycle system. However, the operational conditions of the turbine often deviate from its design values due to changes of the heat source or the cooling conditions, and such deviates may deteriorate the flow behavior and degrade the turbine performance. To enhance the turbine efficiency at complex conditions for flexible running of the Kalina cycle system, a multipoint design optimization method is developed: the flexible operating has been defined by three critical, dimensionless parameters, which cover a wide range in a 3D operating space; the representative off-design points are identified to define the objective function; and adaptive optimization methods are integrated to permit optimization searching using limited CFD callings. The developed multipoint design method is adopted to improve the turbine performance under complex operating conditions. The obtained results demonstrate that the application of the developed multipoint optimization method effectively eliminates the flow separation at various operating conditions; thus, the turbine off-design performance has been comprehensively improved.

Preliminary Design and Blade Optimization of a Two-Stage Radial Outflow Turbine for a CO2 Power Cycle

Recently, the CO2 power cycle has attracted attention because of tightening environmental regulations. The turbine is a factor that greatly affects the efficiency of the cycle. The radial outflow turbine is a turbomachine with the various advantages of an axial flow turbine and a radial inflow turbine, but the design theory for the turbine is uncertain. In this study, a preliminary design algorithm for a radial outflow turbine with a multi-stage configuration is presented. To verify the preliminary design algorithm, a preliminary design for a two-stage radial outflow turbine for a CO2 power cycle was carried out, and a computational fluid dynamic analysis was performed. Consequently, values close to the target performance were obtained, but blade optimization was performed to obtain more satisfactory results. The final geometry of the radial outflow turbine was obtained through optimization considering the blade exit angle related to the deviation angle, blade maximum thickness-true chord ratio, and incidence angle. In the final geometry, the error rates of power (W˙), efficiency (ηts), and pressure ratio (PRts) between target performance and computational fluid dynamic results were improved to 5.0%, 4.8%, and 1.8%, respectively. The performance and flow characteristics of the initial and final geometries were analyzed.

Analysis of radial-outflow turbine design for supercritical CO2 and comparison to radial-inflow turbines

Cycles using supercritical carbon dioxide have been recognized as potential future power technology. However, the turbines in these systems tend to experience very high rotational speeds and entail small physical sizes, which can affect on the overall feasibility. One turbine type having potential to overcome some of the described challenges is the radial outflow turbine. However, its use in supercritical carbon dioxide power systems has not yet been extensively studied since typically axial or radial inflow turbines are considered instead. In this paper, the design of radial-outflow turbines with supercritical carbon dioxide is carried out and the results are compared to the respective radial inflow turbine designs. The analysis was carried out with turbine inlet temperature of 600 °C, inlet pressure of 200 bar and outlet pressure of 78 bar. Designs with four mass flow rates were investigated to study the effect of the power scale on the turbine design and losses. The geometry, efficiency, rotor stress and axial force were defined and analyzed for each design case. The results show that both the investigated turbine types can reach high isentropic efficiencies ranging from about 85% to over 90%. The radial outflow turbines can reach high efficiencies at wider specific speed range whereas the efficiency of radial inflow turbine is reduced more steeply, as the design speed is changed from its optimal value. Radial outflow turbines also reach high efficiencies with lower design speeds and that can be considered advantageous, since it helps to reduce the challenges related to turbomachinery rotordynamic and mechanical design. As a conclusion of the study, it is suggested that the use of radial outflow turbines can increase the feasibility of supercritical carbon dioxide power systems at the examined power scales.

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.

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%.

선박폐열회수시스템을 위한 외향반경류형 터빈 기본 설계

Based on the IMO 2020 Regulation and EEDI Phase 3, international demand for eco-friendly ships is growing. The waste heat recovery system on vessels has a potential to reduce CO₂ emissions of 5 to 10% while improving engine efficiency. This study aims to design ORC (Organic Rankine Cycle) and radial outflow turbine for the waste heat recovery system using exhaust gas in vessels. A designed cycle is simple ORC using R245fa as a working fluid. 1D turbine design utilizes Euler`s turbomachinery equation, specific speed, specific diameter and commercial software. Once the initial model of the ROT (Radial Outflow Turbine) was designed, a case study was conducted by different numbers of stage. For a case study, we chose a 5-stage ROT and analyzed its design and off-design performances using rotational speed, inlet total pressure and temperature. The designed 5-stage ROT has the power output of 480.9 kW and total-to-static efficiency of 86.8% at the design point. The off-design performance can be a preliminary guidance to operate an ROT in practice.

Design and verification of a hermetic high-speed turbogenerator concept for biomass and waste heat recovery applications

Many waste heat recovery and biomass applications offer opportunities for small-scale steam turbines to produce electricity and to improve systems’ energy efficiency. However, the currently used axial turbine-based technology is generally characterized by a relatively large physical size and poor design and off-design performances. To overcome these challenges, a new compact water-cooled high-speed radial outflow turbine concept is proposed. While the previous understanding of the chosen novel rotor water cooling approach indicates general system feasibility, improved turbine performance, and good potential, the scientific literature lacks relevant information. Since the design of high-speed machines is always case-dependent, every concept must be verified. Hence, to provide verification and new scientific information, this study combines analytical, numerical, and experimental analyses. The results predict turbine performance levels comparable with the previous radial outflow design, and its efficiency was found to exceed those of conventional turbines. During the experiments, the turbine also produced electricity from poor-quality steam, and its rotor dynamic behavior and magnetic bearing performance were close to the predicted results. These findings are considered a verification of the proposed concept. Furthermore, the rotor water cooling approach improved the stability of the system operation and although its physical behavior was not fully resolved, the study was able to verify its feasibility. In addition, at below 200 €/kW, the turbogenerator costs are competitive against competing technologies.

Optimal Design of a Ljungström Turbine for ORC Power Plants: From a 2D model to a 3D CFD Validation

In the last few years, waste-energy recovery systems based on the Organic Rankine Cycle (ORC) have gained increased attention in the global energy market as a versatile and sustainable technology for thermo-electric energy conversion from low-to-medium temperature sources, up to 350 °C. For a long time, water has been the only working fluid commercially adopted in powerplants: axial and, for smaller machines, radial inflow turbines have been the preferred expanders since their gulp capacity matches the ρ-T curve of water steam. The density of most organic compounds displays extremely large variations during the expansion (and the volume flow rate correspondingly increases along the machine channels), so that Radial Outflow Turbines (ROTs) have been recently considered instead of traditional solutions. This work proposes a two-dimensional inviscid model for the stage optimization of a counter-rotating ROT, known as the Ljungström turbine. The study starts by considering five different working fluids that satisfy both the gulp requirements of the turbine and the hot source characteristics. On the basis of a limited number of geometric assumptions and for a fixed set of operating conditions, different kinematic parameters are optimized to obtain the most efficient cascade configuration. Moreover, as shown in the conclusions, the most efficient blade profile leads to higher friction losses, making further investigation regarding the best configuration necessary.

Preliminary Design and Off-Design Analysis of a Radial Outflow Turbine for Organic Rankine Cycles

Recently, the advantages of radial outflow turbines have been outstanding in various operating conditions of the organic Rankine cycle. However, there are only a few studies of such turbines, and information on the design procedure is insufficient. The main purpose of this study is to provide more detailed information on the design methodology of the turbine. In this paper, a preliminary design program of a radial outflow turbine for organic Rankine cycles was developed. The program determines the main specifications of the turbine through iterative calculations using the enthalpy loss model and deviation angle model. For reliability evaluation of the developed algorithm, a 400.0 kW turbine for R143a was designed. The designed turbine was validated through computational fluid dynamics. As a result, the accuracy of the program was about 95% based on the turbine power, which shows that it is reliable. In addition, the turbine target performance could be achieved by fine-tuning the blade angle of the nozzle exit. In addition, performance evaluation of the turbine against off-design conditions was performed. Ranges of velocity ratio, loading coefficient, and flow coefficient that can expect high efficiency were proposed through the off-design analysis of the turbine.

Design, Optimization, and Analysis of Supersonic Radial Turbines

Abstract New compact engine architectures such as pressure gain combustion require ad hoc turbomachinery to ensure an adequate range of operation with high performance. A critical factor for supersonic turbines is to ensure the starting of the flow passages, which limits the flow turning and airfoil thickness. Radial outflow turbines inherently increase the cross section along the flow path, which holds great potential for high turning of supersonic flow with a low stage number and guarantees a compact design. First, the preliminary design space is described. Afterward a differential evolution multi-objective optimization with 12 geometrical design parameters is deducted. With the design tool autoblade 10.1, 768 geometries were generated and hub, shroud, and blade camber line were designed by means of Bezier curves. Outlet radius, passage height, and axial location of the outlet were design variables as well. Structured meshes with around 3.7 × 106 cells per passage were generated. Steady three-dimensional (3D) Reynolds-averaged Navier–Stokes (RANS) simulations, enclosed by the k-omega shear stress transport turbulence model were solved by the commercial solver CFD++. The geometry was optimized toward low entropy and high-power output. To prove the functionality of the new turbine concept and optimization, a full wheel unsteady RANS simulation of the optimized geometry exposed to a nozzled rotating detonation combustor (RDC) has been performed and the advantageous flow patterns of the optimization were also observed during transient operation.

외향 반경류 터빈의 예비설계에 관한 기초연구

외향 반경류 터빈의 예비설계에 관한 기초연구

Field performance evaluation of geothermal ORC power plants with a focus on radial outflow turbines

The calculation of the performance of an ORC (Organic Rankine Cycle) and its components (in particularly the turbine) is generally not a trivial task because of the lack of a proper instrumentation, the inaccuracy of the available measurements and the uncertainty on fluid thermodynamic properties calculation. These limitations can greatly affect the final computed results especially for complex fluids with a small temperature drop in expansion. A strategy to solve the inconsistency of the measured data set is to verify the energy and mass balance of each component and of the overall plant using also information related to the geometry of specific components, primarily the turbine as well as electrical measurements. After a brief description of the radial outflow turbine and of its main features, two operating geothermal ORC (Organic Rankine Cycle) plants installed by Exergy Spa in Turkey are described. For both plants a methodology for the consistency check of the experimental data set is presented with a description of the installed instrumentation, the test procedure and methods used to calculate the turbine efficiency as well as the overall power cycle performance.

Design and performance analysis of three stage centrifugal turbine

In this paper, the three-stage centrifugal turbine was designed based on the thermodynamic parameters of a four-stage test axial turbine. 1D aerodynamic design, 3D numerical simulation and optimization, and analysis on off-design performance of the centrifugal turbine were conducted. The results show that the key simulation parameters including total-static efficiency, shaft power, reaction degree, velocity ratio and pressure ratio of turbine stages are close to the 1D calculation values; at the design condition, streamline is smooth in the passage of turbine cascades; high efficiency has been obtained, indicating that the aerodynamic performance of three-stage centrifugal turbine meets the designed requirements. In off-design condition, the total-static efficiency of the designed turbine increases with the increase of pressure ratio first and then decreases; the shaft power decreases with the increase of pressure ratio; the mass flow rate increases gradually with the decrease of pressure ratio and finally tends to be constant when the turbine is under the blocking condition; the variation trend of total-static efficiency, shaft power, mass flow rate with the pressure ratio is similar at different speeds. The total-static efficiency, shaft power and mass flow rate of centrifugal turbine are almost equal to those of the axial turbine at design condition. The total-static efficiency of radial outflow turbine is close to that of axial flow turbine at different pressure ratio, but the mass flow rate of centrifugal turbine is smaller than that of axial flow turbine.

Study on applicability of radial-outflow turbine type for 3 MW WHR organic Rankine cycle

The article presents the results of study on the reasonability of using radial-outflow turbines in ORC. Peculiarities of radial-outflow turbine design utilizing modern design technologies and application to ORC was considered in the first part of the paper. The second part of the paper describes the selection process of the best turbine type for a 3 MW WHR ORC power unit for an internal combustion engine. The selection was performed among different turbine types, like radial-inflow, axial and radial-outflow turbines which were designed with given boundary conditions. The advantages and disadvantages of their application were shown. Eventually, the recommendations regarding application of different turbine types for a 3 MW WHR Organic Rankine Cycle were given. For this particular cycle design, turbines of radial-outflow type were chosen. Their application enables the increase of mechanical output power by 11 % compared to original radial-inflow turbines.

Field Performance Evaluation of ORC Geothermal Power Plants Using Radial Outflow Turbines

This paper, after a brief description of the radial outflow turbine and of its main features, discloses the field performances evaluation of two operating geothermal ORC (Organic Rankine Cycle) plants installed by Exergy Spa in Turkey. The work describes the test procedure, the measurements and calculation methods used to obtain the turbine efficiency as well as overall power cycle performance from the set of available experimental data.

Cycle and turbine re-optimization on geothermal resources significantly deviating from the expected conditions

The economic success of a geothermal exploration program lies in finding the right compromise between exploration costs, risk evaluation analysis and execution timespan. It could frequently happen that the preliminary well test results differ from the real long term operating conditions and in addition they usually vary across the years. The purpose of this study is to analyze the effect of changing resources on performances, in several scenarios with different optimal cycle and turbine design. This study will point out that the re-engineering of the first stage of the radial outflow turbine, the so called "nose cone", may recover a big part of the inefficiencies and lead back to a nearly optimal power conversion, with heavily reduced effects on timeframe and costs, compared to other solutions, like the re-design of the whole turbine.