Experimental Investigation of Flow Fields in a Turbine Cascade with Endwall Film-Cooling Upstream of Leading Edge

Aerodynamic measurements,thermal tracing and surface flow visualization were carried out in a large scale low speed turbine cascade with single and double row injection on the endwall upstream of the leading edge.The detailed flow fields in the cascade,spacial distribution of cooling air and flow patterns on the endwall with coolant injection at blowing ratio 1～3 were obtained.In conjunction with the previously measured flow fields without cooling injection,the obtained results reveal that the flow fields in the cascade are obviously changed by endwall film cooling,and blowing ratio is a vital factor dominating the behavior of the injected coolant and secondary flow in the passage.It was also shown that the interaction between the two rows of injection makes the coolant air press closer to the endwall than with single row injection.The coolant injected at low blowing ratio could not reach the pressure side and was rolled up by the secondary flow.Medium blowing ratio injection can suppress the secondary flow effectively and tends to turn the endwall streamlines toward the inviscid streamlines and make perfect coverage of coolant on the endwall.The injection at high blowing ratio can throw the coolant onto the pressure surface,and even reverse the secondary flow and create a passage vortex with the rotation sense contrary to that of the traditional passage vortex in case of double row injection.