A Study of the Three-Dimensional Unsteady Real-Gas Flows Within a Transonic ORC Turbine

Wheeler, Andrew P. S.; Ong, Jonathan

doi:10.1115/gt2014-25475

Cited by 28 publications

(20 citation statements)

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“…The fluid-dynamic losses in the stator are significantly larger than those in the rotor, confirming the results reported in Ref. [9] for a medium power capacity ORC radialinflow turbine. More in detail, the major loss contribution in the stator is due to the wake mixing downstream of the vane TE, while the fluid dynamic penalty in the rotor is mainly due to endwalls dissipation, secondary flow-induced mixing and tip-leakage flow.…”

Section: 22supporting

confidence: 89%

“…On the other hand, achieving high expansion efficiency is particularly challenging: the combined effect of high-pressure ratio (order of 30-50) and low speed of sound characteristic of organic vapors used in hightemperature ORC applications [2] leads to the design of machines with a supersonic radial stator and a transonic mixed-flow rotor, whose design is further complicated by their small dimensions. It follows that the design rules developed for more conventional radial turbines [3][4][5] are arguably inapplicable to this type of expanders, as opposed to mini-ORC radial inflow turbines for low-enthalpy applications [6] or those designed for larger power capacity, which feature moderate expansion ratios, in general not exceeding 12 [7][8][9].…”

Section: Introductionmentioning

confidence: 99%

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Design Method and Performance Prediction for Radial-Inflow Turbines of High-Temperature Mini-Organic Rankine Cycle Power Systems

Servi

Burigana

Pini

et al. 2019

Journal of Engineering for Gas Turbines and Power

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The realization of commercial mini organic Rankine cycle (ORC) power systems (tens of kW of power output) is currently pursued by means of various research and development activities. The application driving most of the efforts is the waste heat recovery from long-haul truck engines. Obtaining an efficient mini radial inflow turbine, arguably the most suitable type of expander for this application, is particularly challenging, given the small mass flow rate, and the occurrence of nonideal compressible fluid dynamic effects in the stator. Available design methods are currently based on guidelines and loss models developed mainly for turbochargers. The preliminary geometry is subsequently adapted by means of computational fluid-dynamic calculations with codes that are not validated in case of nonideal compressible flows of organic fluids. An experimental 10 kW mini-ORC radial inflow turbine will be realized and tested in the Propulsion and Power Laboratory of the Delft University of Technology, with the aim of providing measurement datasets for the validation of computational fluid dynamics (CFD) tools and the calibration of empirical loss models. The fluid dynamic design and characterization of this machine is reported here. Notably, the turbine is designed using a meanline model in which fluid-dynamic losses are estimated using semi-empirical correlations for conventional radial turbines. The resulting impeller geometry is then optimized using steady-state three-dimensional computational fluid dynamic models and surrogate-based optimization. Finally, a loss breakdown is performed and the results are compared against those obtained by three-dimensional unsteady fluid-dynamic calculations. The outcomes of the study indicate that the optimal layout of mini-ORC turbines significantly differs from that of radial-inflow turbines (RIT) utilized in more traditional applications, confirming the need for experimental campaigns to support the conception of new design practices.

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Section: 22supporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Design Method and Performance Prediction for Radial-Inflow Turbines of High-Temperature Mini-Organic Rankine Cycle Power Systems

Servi

Burigana

Pini

et al. 2019

Journal of Engineering for Gas Turbines and Power

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“…This allowed the Prandtl-Meyer function ν to be formulated as a function of k. The nozzle designs that resulted from this model were validated using CFD, before being implemented within an ORC turbine stator. Later this design model was used to study unsteady effects in ORC turbines [24].…”

mentioning

confidence: 99%

Working-Fluid Replacement in Supersonic Organic Rankine Cycle Turbines

White

Markides

Sayma

2018

Journal of Engineering for Gas Turbines and Power

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In this paper, the effect of working-fluid replacement within an organic Rankine cycle (ORC) turbine is investigated by evaluating the performance of two supersonic stators operating with different working fluids. After designing the two stators, intended for operation with R245fa and Toluene with stator exit absolute Mach numbers of 1.4 and 1.7, respectively, the performance of each stator is evaluated using ANSYS cfx. Based on the principle that the design of a given stator is dependent on the amount of flow turning, it is hypothesized that a stator's design point can be scaled to alternative working fluids by conserving the Prandtl–Meyer function and the polytropic index within the nozzle. A scaling method is developed and further computational fluid dynamics (CFD) simulations for the scaled operating points verify that the Mach number distributions within the stator, and the nondimensional velocity triangles at the stator exit, remain unchanged. This confirms that the method developed can predict stator performance following a change in the working fluid. Finally, a study investigating the effect of working-fluid replacement on the thermodynamic cycle is completed. The results show that the same turbine could be used in different systems with power outputs varying between 17 and 112 kW, suggesting the potential of matching the same turbine to multiple heat sources by tailoring the working fluid selected. This further implies that the same turbine design could be deployed in different applications, thus leading to economy-of-scale improvements.

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“…As the organic fluid properties are totally different from air, these researches are mainly divided into two technical routes. One route focuses on forward design, including preliminary design of geometry parameters and aerodynamic design of blade profiles [12][13][14][15][16][17][18][19][20][21]. Dolz et al [13] propose that the pre-design of turbomachinery must take real gas equations of state into consideration, because the specific energy deviation between real gas and perfect gas can be as large as 100%, which may lead to total wrong turbine preliminary design result.…”

Section: Introductionmentioning

confidence: 99%

“…The results showed that a nozzle geometry with much higher exit-to-throat area ratio was required to obtain an efficient expansion. Wheeler and Ong [14,15] mainly focus on the radial turbine rotor flow mechanisms and geometry optimizations by the CFD tools. They suggested that small changes in the inducer shape had a significant effect on turbine efficiency due to the development of supersonic flows in the rotor.…”

Section: Introductionmentioning

confidence: 99%

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

Zhang

Zhuge

Zhang

et al. 2017

Entropy

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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.

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A Study of the Three-Dimensional Unsteady Real-Gas Flows Within a Transonic ORC Turbine

Cited by 28 publications

References 0 publications

Design Method and Performance Prediction for Radial-Inflow Turbines of High-Temperature Mini-Organic Rankine Cycle Power Systems

Design Method and Performance Prediction for Radial-Inflow Turbines of High-Temperature Mini-Organic Rankine Cycle Power Systems

Working-Fluid Replacement in Supersonic Organic Rankine Cycle Turbines

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

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