Dynamics of Coherent Structures and Random Turbulence in Pressure Side Film Cooling on a First Stage Turbine Vane

This paper is based on a combined experimental and numerical investigation on pressure side film cooling in a high pressure turbine vane. The pressure side cooling geometry exhibits two staggered rows of cylindrical holes and a trailing edge cutback, fed by the same plenum chamber. The investigated conditions refer to low speed (exit isentropic Mach number of Ma_2is = 0.2) and low turbulence intensity data. The choice of one only coolant-to-mainstream mass flow ratio equal to MFR = 1.5% was dictated by the hole discharge: on the one side, mainstream injection into the cooling holes and, on the other side, jet liftoff were avoided to get an effective thermal coverage downstream of the holes. Stress-Blended Eddy Simulation (SBES) model has been used to capture the unsteady physics of cooling jet-mainstream interaction downstream of each cooling row and cutback slot. The focus is on SBES capability of developing vortical structures at the interface between coolant and mainstream, as a function of local coolant-to-mainstream velocity ratio, because of their ultimate effect on vane surface temperature. Special attention has been paid to the shape and dynamics of coherent unsteadiness: SBES provided evidence of shear layer Kelvin-Helmholtz instability and hairpin vortices, downstream of cooling holes, with a Strouhal number (St) of 1.3 and 0.3–0.4, respectively. Simulated vortex shedding in the cutback region was characterized by St of 0.32, to be compared against the measured St value of 0.40.