Flow characteristics of an axial turbine with chamber and diffuser adopted in compressed air energy storage system

Abstract

Axial turbine is an important work-output device in Compressed Air Energy Storage (CAES) system. A compact chamber and a short diffuser are both adopted in the turbine to obtain higher power with lower investment. As a result, the internal flow field is also influenced significantly. In present study, internal flow characteristic of an axial turbine adopted in a new 10MW CAES system is analyzed with compact chamber and short diffuser by three-dimensional steady numerical method. The results illustrate that the isentropic efficiency obtained by the numerical method agrees well with the experiment. Analysis of aerodynamic performance indicates that maximum entropy increase is found in rotor, and the flow loss in stator also cannot be neglected. Back flow with lower velocity, higher static pressure and entropy is observed near bottom of the chamber, and non-uniform distribution of total pressure is thus formed at outlet of chamber. As a result, obvious variation of inlet attack angle of stator is observed along spanwise and circumferential direction, the entropy in stator is thus increased by 33.17%. Fluid with velocity of 23m/s is found at outlet of diffuser, which causes higher leasing velocity loss. The struts significantly reduces the pressure recover ability of diffuser by 11.42%. However, higher pressure recovery coefficient can be obtained at 0.035 m ∼ 0.135 m along axial distance of diffuser when actual inlet swirl angle is applied.