Combined Experimental and Numerical Study of Showerhead Film Cooling in a Linear Nozzle Vane Cascade

In this paper showerhead film cooling performance measured on a first stage nozzle guide vane within a linear cascade are presented and compared against steady and unsteady CFD simulations. A showerhead cooling scheme was tested at blowing ratios of BR = 2 to 4 under engine-like conditions (i.e. nominal exit Mach number of Ma_2is = 0.42 and high mainstream turbulence level). Adiabatic film cooling effectiveness in the leading edge region was measured by means of wide banded Thermochromic Liquid Crystals. A borescope was used to overcome the constraints to the optical access imposed by the turbulence generator. Moreover, exit surveys detailing total pressure downstream of the cooled vane were acquired using a five-hole miniaturized aerodynamic pressure probe. In view of qualitative/quantitative validation purposes, numerical modelling based on steady RANS and Detached Eddy Simulation (DES) approach was performed for the lowest investigated BR of 2.0, which provided the best film coverage. Nevertheless the dilution of the coolant jets from the showerhead was predicted by DES, agreement with the measured cooling effectiveness in the leading edge region was still far from being achieved. Instead, the steady approach was enough to capture aerodynamic features such as vane load, wake loss and plenum to mainstream pressure ratio.