Experimental and numerical studies on enhanced effusion cooling with shallowly dimpled film holes on double-wall structure surface

Abstract

This paper presents a flow and heat transfer investigation on multi-row dimpled film cooling in the double-wall configuration, considering important flow and geometrical characteristics including internal narrow jet impingement channel and outer film cooling with shallowly dimpled holes. The film cooling hole has dimpled exit, with the dimple depth to diameter ratio of 0.2. The inclined angle of the film hole is 30 degree and film hole length to diameter ratio is 3.0. The adiabatic film cooling effectiveness and heat transfer characteristics on the external surface are obtained by using transient infrared thermography measurement technique, which is based on the Impulse Response Method. And steady-state numerical computations using the Shear Stress Transport (SST) k-ω turbulence model were carried out respectively with the experimentally related adiabatic wall boundary conditions and with the fluid–solid conjugated boundary conditions, which provides the turbulent flow structure and overall cooling performance of the double-wall structure. The experimental results indicate that compared to the counterpart cylindrical film holes, the dimpled film holes can expand the spanwise coverage of coolant film, and the adiabatic film cooling effectiveness was improved by 66 %, 82 % and 180 % respectively at BR = 0.3, 0.6 and 1.0. Therefore, the dimpled holes can improve the film cooling effectiveness significantly. The numerical simulations indicated that the dimpled film holes influence the jet-in-crossflow structure and film cooling effectiveness significantly through complex interactions of the coolant jets, mainstream flow and dimpled wall. The overall cooling effectiveness of the double-wall structure with dimpled film holes on the thermal barrier coating can be distinctively improved by about 12.8 % over the case with conventional cylindrical film holes, which was indicated in the conjugated simulations under the blowing ratio of 1.0 and the mainstream-coolant temperature ratio of 2.0.