Experimental and numerical investigations on the unsteady flow and film cooling characteristics of the trailing edge cutback

Abstract

The film cooling characteristics of the trailing edge cutback slot of a high pressure turbine were experimentally and numerically investigated. The unsteady flows have an important effect on the mixing process of the mainstream and coolant flow, resulting in deteriorated film performance. To illustrate the interaction between the unsteady flows and coolant injection, eight blowing ratios ranging from 0.3 to 1.2 were considered for the baseline cases. Pressure sensitive paint measurements were conducted to acquire the adiabatic film cooling effectiveness distribution. The counter-intuitive decrease of the film cooling effectiveness was confirmed and further revealed. Particle image velocimetry showed that the unsteady flow patterns downstream of the trailing edge slot varied with increasing blowing ratio. Furthermore, the high-fidelity RANS/LES hybrid method was employed to resolve the detailed flow fields. The numerical method was carefully validated, and it successfully predicted the unsteady flows and mixing process. The spanwise vorticity showed that the two branches of the shedding vortices alternatively become strong. At the blowing ratio of 0.75, the strength of the two branches was comparative, yielding the worst cooling performance. Additionally, the density ratio and lip thickness to slot height ratio were investigated. Thus, the density ratio affects the coolant velocity ratio, causing the forward movement of the inflection point of the film cooling effectiveness map. The decrease of the lip thickness to slot height ratio leads to the reduction of the strength of the shedding vortices and therefore increases the film cooling effectiveness.