Helium Turboexpander for Cryogenic Refrigeration and Liquefaction Cycles: Transient Analysis of Rotor–Stator Interaction
20 Sep 2016-
About: The article was published on 2016-09-20. It has received 4 citations till now. The article focuses on the topics: Turboexpander & Liquefaction.
Citations
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TL;DR: In this paper, a three-dimensional transient flow analysis of a turboexpander for helium refrigeration and liquefaction cycles was performed using Ansys CFX®, to understand the flow field of a high-speed helium turboexpanders, which in turn will help in taking appropriate decisions regarding modifications of established design methodology for improved efficiency of these machines.
17 citations
TL;DR: In this paper, three-dimensional unsteady flow analysis of a high speed microturbine used in helium applications was carried out using Ansys CFX® and the loss generated by the various secondary and vortical flows for the different cases was quantified in terms of entropy loss coefficient.
Abstract: The complex flow characteristics in a high-speed helium microturbine used in cryogenic refrigeration and liquefaction cycles are highly influenced by the effects of rotation In order to enhance the turbine performance and to improve the preliminary design process of the turboexpander, the flow characteristics within the turbine blade passage need to be investigated at different rotational speeds Here, three-dimensional unsteady flow analysis of a high speed cryogenic microturbine used in helium applications was carried out using Ansys CFX® The loss generated by the various secondary and vortical flows for the different cases was quantified in terms of entropy loss coefficient The loss generating mechanism was also assessed by analysing the velocity vectors, entropy contours and the behaviour of the vortex cores With change in speed the influence of scraping flow due to relative casing motion and the blade loading on the flow characteristics was found to vary significantly At lower speeds, the scraping flow decreases and thus augments the tip leakage flow which in turn interacts with the suction side leg of the leading edge vortex to form a single large vortex This combined vortex increases the velocity defect and thus leads to increased loss generation The analysis of the vortex core velocity and the blade loading diagram revealed the need for modifications in blade profile for improved turbine performance Furthermore, the comparison of the CFD results with the Balje's nsds chart showed remarkable variations, the results of which can be used to modify the chart for the design of efficient cryogenic microturbines for helium applications
11 citations
01 Feb 2017
TL;DR: In this article, transient CFD analyses of a cryogenic turboexpander designed for helium refrigeration and liquefaction cycles using Ansys CFX® were performed to investigate the effect of trailing edge thickness on the turboexpanders performance and the performance characteristics and the flow patterns were compared to understand the flow characteristics in each case.
Abstract: Turboexpanders in cryogenic refrigeration and liquefaction cycles, which is of radial inflow configuration, constitute stationary and rotating components like nozzle, a rotating wheel and a diffuser. The relative motion between the stationary and rotating components and the interactions of secondary flows and vortices at different stages make the turboexpander flow unsteady. Computational Fluid Dynamics (CFD) analysis of this flow is essential to identify the scope for improvement in efficiency. The trailing edge vortex formed due to the mixing of the pressure and suction side streams is an important phenomenon to analyse, as this leads to efficiency degradation of the machine. Additionally, there are mechanical vibrations and dynamic loading associated with. This flow non-uniformity at the exit should be suppressed as this may affect the pressure recovery process in the diffuser and thereby the turboexpander's performance. The strength of this vortex depends upon the geometrical parameters like trailing edge shape, thickness etc. In this paper, transient CFD analyses of a cryogenic turboexpander designed for helium refrigeration and liquefaction cycles using Ansys CFX® were performed to investigate the effect of trailing edge thickness on the turboexpander performance and the performance characteristics and the flow patterns were compared to understand the flow characteristics in each case.
1 citations
TL;DR: In this article, an economic evaluation of the reverse Brayton cycle-based refrigerator has been performed for 10 kW range cooling capacity at 65 K. The significant finding of this analysis is that component performance, the turbine being the major one, needs to be improved to meet the economic criteria of 25 $/W as enumerated in the cryogenic road map for high-temperature superconductor cooling.
Abstract:
In this article, by using exergoeconomic approach, an economic evaluation of reverse Brayton cycle-based refrigerator has been performed for 10 kW range cooling capacity at 65 K. One of the typical application domains of this refrigerator at the considered heat load is cooling of high-temperature superconductor for future power transmission lines that are in the developmental phase in different parts of the world. Multi-objective optimization and sensitivity analysis have been performed to investigate the sources of cost attached to the exergy destruction. Based on exergoeconomic evaluation parameters, recommendations have been provided for deciding the cost-effective design parameters for refrigerators. The significant finding of this analysis is that, for the basic reverse Brayton cryocooler, component performance, the turbine being the major one, needs to be improved to meet the economic criteria of 25 $/W as enumerated in the cryogenic road map for high-temperature superconductor cooling. The exergoeconomic design applied on the reverse Brayton refrigerator for high-temperature superconductor cables cooling can be adapted for other applications such as recondensation and liquefied natural gas cold energy utilization.
References
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TL;DR: The role of the concepts behind the SST model in current and future CFD simulations of engineering flows is outlined and the overall turbulence modelling strategy for ANSYS computational fluid dynamics (CFD) is outlined.
Abstract: The present author was asked to provide an update on the status and the more recent developments around the shear-stress transport (SST) turbulence model for this special issue of the journal. The article is therefore not intended as a comprehensive overview of the status of engineering turbulence modelling in general, nor on the overall turbulence modelling strategy for ANSYS computational fluid dynamics (CFD) in particular. It is clear from many decades of turbulence modelling that no single model-nor even a single modelling approach-can solve all engineering flows. Any successful CFD code will therefore have to offer a wide range of models from simple Eddy-viscosity models through second moment closures all the way to the variety of unsteady modelling concepts currently under development. This article is solely intended to outline the role of the concepts behind the SST model in current and future CFD simulations of engineering flows.
693 citations
Book•
01 Jan 2006
TL;DR: In this paper, the authors provide a thorough description of actual, working aerodynamic design and analysis systems for both axial-flow and radial-flow turbines, for both types of turbines.
Abstract: This book provides a thorough description of actual, working aerodynamic design and analysis systems, for both axial-flow and radial-flow turbines. It describes the basic fluid dynamic and thermodynamic principles, empirical models and numerical methods used for the full range of procedures and analytical tools that an engineer needs for virtually any type of aerodynamic design or analysis activity for both types of turbine. The book includes sufficient detail for readers to implement all or part of the systems. The author provides practical and effective design strategies for applying both turbine types, which are illustrated by design examples. Comparisons with experimental results are included to demonstrate the prediction accuracy to be expected. This book is intended for practicing engineers concerned with the design and development of turbines and related machinery.
203 citations
20 Apr 2009
TL;DR: Flow modeling basics are reviewed in this survey including a summary of the flow processes observed in nature and the development of a variety of different loss, blockage, and deviation models is reviewed.
Abstract: Analytical modeling of turbomachinery components and systems has been used for more than a century to develop new machines and understand internal flow states. Flow modeling basics are reviewed in this survey including a summary of the flow processes observed in nature. The development of a variety of different loss, blockage, and deviation models is reviewed, and the complexity of mathematical data processing and model development is presented. Examination of different modeling philosophies is given with critique of the consequences. Examples of data matching, modeling for design work, and modeling uncertainty are given. Suggestions for future improvements are offered.
22 citations
Dissertation•
22 Mar 2002
15 citations
01 Dec 2008
TL;DR: In this paper, the effect of axial gap between rotor and stator on turbine performance and flow field of a single axial flow turbine stage was investigated, where the axial clearance from the downstream end of the stator hub to rotor leading edge was kept constant in order to minimize the influence of the disk cavity to the main flow.
Abstract: The aim of the present study is to investigate effects of the axial gap between rotor and stator upon the stage performances and flow field of a single axial flow turbine stage. In this paper experimental and numerical studies are performed for three axial gaps by moving the stator vane axially. Five-hole probe measurements are made to obtain total pressure loss and time-averaged flow field upstream and downstream of the rotor blades. In addition, large-scale unsteady threedimensional RANS-based numerical simulation, in which blade-count ratio is almost the same as that of the actual turbine stage, is executed to understand interaction between the stator and the rotor. These results show that overall turbine stage efficiency with the smallest axial gap is the highest among the three gaps. This is because the stator wakes are diffused by expanding axial gap, inducing the growth of the secondary flow near the endwall. INTRODUCTION Experimental and numerical studies on unsteady flow effects upon turbine performance have been performed by many researchers to understand the mechanism of the loss caused by several factors such as wake and passage vortices. The unsteady flow field in the turbomachinery is determined by the relative movement of the rotor against the stator, which induces periodic interactions with each other. Unsteady interactions between stator and rotor has received much attention and understanding the flow phenomena by these interactions is very important to clarify the mechanism of loss generation in the turbine stages. Thus, it is necessary to make continual efforts to increase knowledge on the unsteady interaction between stator and rotor in order to achieve further improvement of turbine efficiency. Recently, a lot of studies have been made to investigate the unsteady effects of wake passing upon aerodynamic performance of the turbine stage, and some efforts among them revealed the importance of the unsteadiness and the mechanism of the losses in the tubomachinery. (for example, Pullan(2006), Denos et al.(2001), Hodson et al.(1998)). Furthermore, some works, which intended to achieve much improvement of tubine stage efficiency, have been performed from the viewpoint of turbine stage configuration, such as the solidity (Funazaki et al.(2006)), injection flow angle upstream of the turbine stage(Felipe et al.(2003), Funazaki et al.(2005)). As for the effect of axial gap, Gorrell et al.(2003) presented that in transonic compressors additional losses were produced in narrow axial spacing cases since a shock wave near the rotor leading edge in. teracted with the stator. Gaetani et al.(2006) and Yamada et al.(2006) reported that it was possible to achieve higher turbine efficiency when the axial spacing was decreased. One of the reasons for such trend given by Yamada et al. is that the suppressing effect of counterrotating vortices generated by rotor-stator wake interaction on the passage vortex become weaker by increasing axial spacing. However, further studies are still needed before drawing a general conclusion with respect to the effect of axial gap. This paper therefore provides experimental and numerical investigations of aerodynamic performance and unsteady flow behaviors in a single axial flow turbine stage with three axial gaps. The purpose of this study was to clarify the time-averaged and unsteady effects of the axial gap, where the axial clearance from the downstream end of the stator hub to rotor leading edge was kept constant in order to minimize the influence of the disk cavity to the main flow which otherwise would have happened when the axial gap was expanded. A five-hole probe was used to measure time-averaged flow field and total pressure loss distributions upstream and downstream of the rotor blades. In addition, unsteady three-dimensional Navier-Stokes flow simulations, which was based on an implicit high-resolution upwind scheme using TVD formulation, was performed to elucidate unsteady flow field in the turbine stage and the interaction of the stator and the rotor.
14 citations