Film cooling evaluation of a single array of triangular craters

Abstract

The available database has shown film holes embedded into trench and surface craters demonstrate significant improvements in the film cooling performance over conventional inclined round holes. In this paper two new designs of a single array of round film holes inside triangular craters with a straight and contoured leading edge are evaluated numerically. In terms of geometry this design is derivative of the trench, but seems to be less prone to spallation of the thermal barrier coating, into which craters are usually embedded. The numerical simulation was performed using RANS approach along with SST turbulence closure. The single array of 4 triangular craters was used in calculations. The non-dimensional triangular crater depth h/d was 0.5, hole pitch t/d – 3.0, the channel height in which a single array of triangular craters was placed on the bottom adiabatic wall – 10 mm. The mainstream flow speed V∞ in front of the crater array was 37 m/s (Re2H = 28000), inlet flow temperature – 20°C, coolant temperature – 80°C (reverse flow scheme was studied), and flow turbulence – 1%. The coolant supply into array of triangular craters with a straight leading edge provides remarkable film cooling effectiveness growth, which is below of trench data. This design demonstrates the permanent growth in spatially averaged film cooling effectiveness with blowing ratio increase. The contoured (convexly-curved) leading edge of triangular craters improves slightly the film cooling performance both on the initial and transitional areas of the adiabatic wall. As far as the coolant supply into a single array of hemispherical or cylindrical craters of the same depth, they are well below of triangular craters data.