Experimental Study of Heat Transfer and Film Cooling Performance of Upstream Ejected Coolant on a Turbine Endwall

An upstream coolant injection that is different from the known leakage flow was introduced to protect the turbine endwall. This coolant is ejected tangentially from a row of cylindrical holes situated at the side of a backward-facing step. In this experiment, the effects of mass flow ratio and leakage slot width on the endwall heat transfer characteristics were investigated. The dimensionless heat transfer coefficient (Nu) and adiabatic film cooling effectiveness (η) on an axisymmetric turbine endwall were measured by the stable-state thermochromic liquid crystal (TLC) technique and the pressure sensitive paint (PSP) technique, respectively. Three mass flow ratios (MFR) of 0.64%, 0.85%, and 1.07%, as well as two leakage slot widths (W) of 3.93 mm, and 7.86 mm were considered. Results indicate that the injection film suppresses the strength of the passage vortex, which leads to the coolant covering almost the entire endwall. This result is more evident for the higher MFR cases, meanwhile, the corresponding averaged film cooling effectiveness is increased with the enhancement of the MFR. However, the case with a higher MFR produces a higher heat transfer coefficient distribution, especially in the region close to the leakage slot edge. Besides, when the W is lower, the endwall presents a higher η and a lower Nu for all the cases, which can guide the optimal design of the endwall.