Experimental study on the film cooling characteristics of the cylindrical holes embedded in sine-wave shaped trench

Experimental investigation has been performed to study the film cooling performance of the cylindrical holes embedded in sine-wave shaped trench. The sine-wave shaped trench is got by changing the trailing edge of the transverse trench into sine-wave shape; the holes are located next to the peaks of the wave. The sine-wave shaped trench hole is expected to get a wider spread of the cooling jet in the span-wise direction. The film cooling effectiveness and discharge coefficient of the sine-wave shaped trench hole configurations with different trench depths (0.75D, 1D) and wave peaks (1D, 2D) have been measured using the transient thermal liquid measurement technique. The blowing ratio covers a range from 0.5 to 2.0. The transverse trench hole was also investigated as a basis of comparison. Thermal and hydrodynamic fields were investigated numerically using Reynolds Averaged Navier Stokes (RANS) simulations with realizable k-ϵ turbulence model and enhanced wall treatment. Results show that downstream the sine-wave shaped trench, the film cooling effectiveness is higher in the region between the holes. That's due to the jet spread wider under the influence of the anti-counter-rotating vortices which caused by the sine-wave shape. With the increasing blowing ratio, the film cooling effectiveness of the sine-wave shaped trench hole increases. The larger trench depth produces higher film cooling effectiveness in the region between the holes. With the increasing wave peak, the film cooling effectiveness is increased in the region between the holes due to that more of the jet flows to the wave valley. The discharge coefficients of the sine-wave shaped trench configurations are higher than the transverse trench which means that the sine-wave shape trench has lower flow resistance.