Effects of non-equilibrium condensation on aerodynamics of the flow field in a steam turbine cascade

Abstract

In the present paper an in-house CFD code is developed using Roe scheme to simulate condensing two-phase flow in blade to blade passage of a steam turbine. Effects of condensation on the flow field of steam turbine rotor tip section are investigated for different outlet pressures. Firstly, comparison is performed between results of wet and dry cases. Then effects of outlet pressure variations on the flow field are studied. Finally effects of condensation on different specifications of the flow field (total pressure loss coefficient, entropy generation and deviation angle) are investigated. Also the mechanism of flow deviation in the cascade flow field is described. Condensation has a great influence on the behavior of the flow field based on the numerical results of this paper. It changes the outflow direction and consequently the flow entering to the next blade deviates from its on-design condition, thus additional losses are produced. For example, the value of deviation angle reaches to 7.62for wet case and exit Mach number Me=1.45. Also there are stagnation pressure loss and entropy generation due to non-equilibrium condensation that reduce the efficiency of the steam turbine