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Publication Title | radial turbine supercritical compressed air energy storage

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Original Article
Flow characteristic of a multistage radial turbine for supercritical compressed air energy storage system
Xing Wang1, Wen Li1, Xuehui Zhang1, Yangli Zhu1, Wei Qin2 and Haisheng Chen1
Abstract
Proc IMechE Part A:
J Power and Energy
0(0) 1–19
! IMechE 2017
Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0957650917743366 journals.sagepub.com/home/pia
Compressed air in supercritical compressed air energy storage system expand from supercritical to atmospheric con- ditions at lower inlet temperature (<500 K) to generate MW scale power. Therefore, a new multistage radial turbine is adopted and the flow characteristic is investigated by numerical simulation. Effects of ideal gas model and tip clearance on the performance and flow field of the multistage turbine are revealed. Results show that ideal gas model can reveal flow pattern under supercritical condition correctly while leading to obvious deviation of isentropic enthalpy drop, entropy, and inlet-to-exit total temperature ratio. Relative differences for mass flow and efficiency are less than 2%, while the relative differences for output power reaches to 9.36%. For shrouded rotor, mixing of working fluid near hub, blade suction surface, and shroud is the main influencing factor of the flow loss in the rotor. For unshrouded rotor, leakage vortex promote mixture of the fluid deriving from the hub, shroud, and suction surface, and causes much higher flow loss in the channel of rotor. The rotors, which have higher blade height variation rate, present higher efficiency reduction when the tip clearance height is increased, which is because the proportion of tip clearance in blade inlet height increases with the increase of average aspect ratio, resulting in the increase of leakage flow at the leading edge of rotor blade. The pressure fluctuation near the tip clearance and efficiency reduction is also increased. The present study provides a reference for further design and optimization of the multistage radial turbines in compressed air energy storage.
Keywords
Compressed air energy storage, multistage, radial turbine, computational fluid dynamics Date received: 26 May 2017; accepted: 28 September 2017
Introduction
Compressed air energy storage (CAES) is a significant technology for energy storage, as it achieves peak power regulation while overcoming the instability of wind and solar energy, which would otherwise hinder energy utilization. These advantages have led to increasing adoption of the CAES system in modern grids,1 renewable energy,2 waste heat utilization,3 and other fields. The basic workflow of the CAES system is simple.4 Electrical energy is converted by com- pressed air from compressors into potential energy. Then, compressed air stored in the tank is released and expanded through the expander to generate elec- tricity again.
As a key component for the expansion process in CAES, the radial turbine, which has a high expansion ratio and a compact structure5 is suitable for the CAES system. The internal flow structure, which influences the aerodynamic performance of radial
turbines, also plays an important role in the efficiency of CAES system. Therefore, many studies have focused on the internal flow structure of radial turbines.
Previous studies have shown that the internal flow structure in radial turbines, which always interact with each other, are complex and varied. An add- itional single vortex called the ‘‘inflow vortex’’ was observed by Putra and Joos6 when they investigated the secondary flow phenomena in a radial turbine nozzle. Zangeneh-Kazemi et al.7 analyzed the flow through a rotor of a radial turbine using a fully
1Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing, PR China
2Institute of Mechanics, Chinese Academy of Sciences, Beijing, PR China
Corresponding author:
Haisheng Chen, Institute of Engineering Thermophysics, Chinese Academy of Sciences, 11 Beisihuanxi Road, Beijing 100190, PR China. Email: chen_hs@mail.etp.ac.cn

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