Influence of axially-convergent contouring on cascade endwall film cooling characteristics in gas turbine

In order to evaluate the influences of the axially-convergent contouring on the endwall film cooling performance of the upstream double-row film holes，the cascade endwall adiabatic film cooling effectiveness was predicted through numerical simulation.The endwall thermal load distribution，adiabatic film cooling effectiveness distribution and secondary flow field were calculated and analyzed for two endwall configurations （flat endwall and axially convergent contoured endwall） at three different blowing ratios （1.0，2.5，3.5） under the simulated realistic operation condition of an industrial gas turbine，inlet turbulence of 16%，exit Mach number of 0.85，exit Reynolds number of 1.5×10⁶，based on “two types of thermal boundaries” numerical method.Simultaneously，the secondary cooling （phantom cooling） phenomenon of the upstream purge flow on the vane surface was noticed.Results showed that compared with the flat end-wall configuration，the axially-convergent contoured endwall reduced the strength of the horse-shoe vortex and endwall thermal load，especially at the region of vane suction surface shoulder.For the axially-convergent contoured endwall，the upstream coolant jets were more efficiently targeted at the endwall，yielding higher endwall adiabatic film cooling effectiveness，especially at the regions of the vane leading edge and vane pressure side where cooling was harder due to the stronger secondary flow.At the increasing blowing ratio，the effects of axially-convergent contouring on endwall film cooling first increased and then decreased.The axially-convergent contouring resulted in a significant increase （up to 35%） in end-wall adiabatic film cooling effectiveness at design blowing ratio of 2.5.The axially-convergent contouring obviously increased the phantom cooling size around the vane leading edge and pressure surface，especially at the region around the vane leading edge （up to 100%，0.1 span at design blowing ratio）.This led to an obvious reduction in the demand of coolant.Therefore，the axially-convergent contoured endwall is an effective approach to increase the endwall adiabatic film cooling effectiveness，reduce the demand of coolant and realize the efficient endwall cooling scheme.