Effect of oscillating flow on two rows of cooling holes with various configurations on film cooling performance

This study investigated the film cooling performance of oscillating flow on two rows of cooling holes with different arrangements under unsteady flow conditions. The effects of the flow oscillations were applied to both the coolant jet and the mainstream at different frequencies ranging from 180 to 2144 Hz at blowing ratios of 0.5, 1.0, and 2.0. Four different arrangements with opposite hole orientation angles and placements were numerically investigated using the Detached Eddy Simulation (DES) turbulence model to measure the film cooling performance and Stanton number ratios (St/Sto). The results indicated that flow oscillation effectively improves the cooling performance of two-row compound angled cooling holes with in-line and staggered configurations. Depending on the frequencies, the oscillation can form a coolant flapping flow that helps counterrotating vortex pair structures penetrate each other. This leads to the complex interaction between vortices, a decrease in jet liftoff, and an improvement in cooling effectiveness throughout the downstream wall. At the frequency of 2144 Hz, the comparison among the four cases reveals that the best spanwise-averaged film cooling effectiveness occurs at the blowing ratio of 1.0 rather than the blowing ratio of 2.0. On the other hand, at the blowing ratio of 0.5, the Stanton number ratios of all cases experienced a remarkable downward trend with increasing frequency up to 1608 Hz, but at the frequency of 2144 Hz, they indicated an upward trend. Moreover, at the blowing ratio of 0.5, the Stanton number ratios of cooling holes with in-line arrangement (cases 1 and 2) and staggered arrangement (case 4) had higher values than others in spanwise and centerline directions at all ranges of frequencies, respectively.