Numerical investigation on the influence of axial thermal expansion in axial turbine for compressed air energy storage system

The starting process of the turbine in compressed air energy storage (CAES) system undergoes a period of thermal expansion, during which the structure of leakage passages is changed, leading to fluctuations in aerodynamic performance. To analyze the variation of aerodynamic performance, leakage flow characteristics, and turbine losses caused by axial thermal expansion, a three-dimensional steady-state numerical simulation of a three-stage high-pressure axial turbine is performed with different axial offsets, and the shroud and disk cavities are included in the computational model. Throughout the axial thermal expansion process, the efficiency tends to increase, followed by a decrease, and then slowly increase with a maximum change of 0.28 %; the power shows the same trend as the efficiency with a maximum change of 0.26 %; the axial thrust firstly increases with a maximum change of 11.7 % and then decreases slowly. The aerodynamic performance is mainly affected by the variations in the flow characteristics of each leakage passage. In addition, compared with shroud leakage, the effect of disk cavity leakage on turbine performance is more significant and is particularly affected by axial thermal expansion.