Effects of inlet misalignment and axisymmetric contouring on endwall heat transfer characteristics in transonic turbine cascade

To evaluate the effects of endwall misalignment and axisymmetric endwall contouring on the endwall heat transfer characteristics in the realistic transonic gas turbine cascade, the guide cascade in the first stage of an industry gas turbine was taken as the research object. The commercial CFD software ANSYS Fluent 15.0 was adopted to numerically investigate the endwall flow and heat transfer characteristics for three types of endwall configurations, including: the simplified flat endwall, the realistic cascade outer endwall (vane shroud) and inner endwall (vane hub) with axisymmetric convergent endwall contouring in axial direction, at the gas turbine design condition (inlet turbulence intensity of 16%, exit Mach number of 0.85). The endwall thermal load distribution, secondary flow field near endwall and backward step vortices development were illustrated and compared for three endwall configurations with two combustor-turbine platform misalignment structures (inlet endwall step height of 0, 6.78 mm). Results showed that compared with the flat endwall configuration, the axisymmetric convergent endwall contouring and upstream endwall misalignment can result in dramatical changes in the endwall secondary flow pattern and thermal load distribution. In general, the axisymmetric convergent endwall contouring can result in a relative reduction in the endwall thermal load, especially for regions of endwall juction around the vane leading edge and downstream the vane throat, where thermal corrosions were more likely caused due to the poor cooling film coverage. In real gas turbine engines, the combustor-turbine endwall misalignment can dramatically enlarge the high thermal load region (upstream the cascade leading edge) which was migrating to the downstream cascade passage, and result in a significant increase (up to 140%) in the heat transfer level. Therefore, the important influences of the endwall contouring and endwall misalignment should be carefully taken into account for the endwall cooling scheme design of the first stage guide cascade in the real gas turbine engines.