Dynamics of coherent structures and random turbulence in pressure side film cooling on a first stage turbine vane

This paper collects the final results of a combined experimental and numerical investigation on pressure side (PS) film cooling in a high-pressure turbine vane, including two staggered rows of cylindrical holes and a trailing edge cutback, fed by one plenum. Having learned that the scale resolving simulation technique is essential to get reasonable predictions of adiabatic film cooling effectiveness, the stress-blended eddy simulation (SBES) model has been selected as the best among the available hybrid RANS-LES options. Mainstream conditions were limited to low speed and low turbulence intensity due to the need of high temporal and spatial resolution. The choice of one only coolantto- 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. SBES potential was evaluated on the basis of qualitative and quantitative characteristics of the flow along the interface between coolant and mainstream because of their ultimate effect on vane surface temperature. The focus was set on shape and dynamics of coherent structures: 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.