Steady and unsteady RANS simulations of heat transfer on a turbine vane endwall with inlet boundary layer skew

Abstract

In this study, steady Reynolds-averaged Navier-Stokes (RANS) and unsteady RANS (URANS) simulations in a turbine vane cascade are performed to study the effects of inlet boundary layer skew on flowfields in the vane passage and heat transfer over the endwall surfaces. The inlet skew simulates the relative movement between rotor platform and stator endwall in a turbine stage. The transverse motion of a moving wall, which is placed parallel to and upstream of the vane endwall, generates the inlet skew. An engine-like velocity profile yields a cascade inlet Reynolds number of 3.46×105. A parametric study is conducted for two moving wall-to-freestream velocity ratios (r) of 0.61 and 0.76, representing the actual operation of an engine. In addition, steady and time-averaged results are compared to address the difference of predictions in heat transfer from the steady and unsteady simulations. The results show that the effects of unsteadiness due to inherent unsteadiness in the flow and inlet skew passage on the pressures over the endwall surface is negligible. However, the unsteadiness plays an important role in determining endwall heat transfer patterns. The inlet boundary layer skew modifies the development and migration of horseshoe vortex and passage vortex, resulting in local variation of heat transfer over most endwall surfaces. Lower heat transfer coefficients are found near the suction side beyond the passage throat, but overall heat transfer levels almost remain the same on the endwall in the presence of inlet skew.