Modelling the influence of vortex shedding on trailing edge cutback film cooling at different blowing ratios

This numerical investigation deals with the capability of unsteady modelling to predict the mixing between the mainstream and the coolant exiting the trailing edge cutback slots in a high pressure turbine nozzle guide vane. The trailing edge cooling features a pressure side cutback with 8 film cooling slots, stiffened by evenly spaced ribs in an inline configuration. Several values of the coolant-to-mainstream mass flow ratio were considered, i.e. MFR = 1.05%, 1.44% and 2%, under incompressible-flow assumption. With a focus on the cases at medium and high MFR, results from the Scale-Adaptive Simulation (SAS) and Detached Eddy Simulation (DES) were compared with experimental measurements including not only cooling effectiveness distributions over the cutback surface but also data from PIV and flow visualizations, with the aim of documenting the inherent instability of the coolant/mainstream flow downstream of the cutback lip. Vortex shedding and cooling effectiveness in the cutback region were reasonably predicted by SAS and DES. However, the simulated thermal coverage at the trailing edge was overestimated for the highest MFR.