Influence of hole geometry on film cooling effectiveness for a constant exit flow area

Abstract

Film cooling is an effective method which can protect the surface from the high temperature environment. Most previous studies have used the same mass flux ratio with different coolant exit flow area for different holes. A better comparison of the film cooling effectiveness would keep the coolant mass flow rate and exit area the same. The present study investigated the effect of hole geometry on the film cooling effectiveness for a constant film cooling exit flow area experimentally and numerically. Four kinds of film cooling holes, the cylindrical hole, the fan-shaped hole, the double jet holes and the hole with sister holes were studied with blowing ratio varied from 0.3 to 1.5. In the experiment, plate surface temperature was measured by an infrared camera and the main flow and coolant flow temperature were measured by thermocouples. To investigate the flow characters, numerical calculation using RNG k−ε turbulence model was performed. Protected wall temperature, film cooling effectiveness and coolant flow stream lines were studied to illustrate the difference between the coolant jets from the four kinds of hole geometries. The results show that film cooling with the other three kinds of holes have an obvious advantage compared to the cylindrical hole. The reason is that for the cylindrical hole, the coolant flow forms a strong vortex pair in the main flow which pulls the hot main flow underneath the coolant flow to lift the coolant jet from the wall, so the cooling effectiveness is very low. For the other three kinds of holes, the mixing between the main flow and the coolant jet forms a complex vortex structure which keeps the coolant jet on the wall, thus improves the cooling effectiveness.