On the flow structures and adiabatic film effectiveness for simple and compound angle hole with varied length-to-diameter ratio by Large Eddy simulation and pressure-sensitive paint techniques

The effects of hole length-to-diameter ratio and compound angle on flat plate film cooling effectiveness are investigated from an experimental and numerical view. Film cooling effectiveness measurements are performed for seven blowing ratios (M) ranging from 0.3 to 2, five-hole length-to-diameter ratios (L/D) from 0.5 to 5, and two compound angles (b: 0 deg and 45 deg) using pressure-sensitive paint (PSP) technique. Results indicate that discrete holes with L=0.5 and 1 show highest film cooling effectiveness regardless of compound angle. Round hole generally shows an increasing trend as L increases from 2 to 5, while compound angle hole shows a complex trend concerning with blowing ratios (BRs) and length-to-diameter ratios. Compound angle enhances film cooling effectiveness with high blowing ratios and length-to-diameter ratios. In a parallel effort, large eddy simulation (LES) approach is employed to solve the flow field and visualize vortex structures of intube and mainstream regions. It is demonstrated that the counter-rotating vortex pair (CRVP) which is observed in the time-averaged flow field is originated in different vortex structures with varying blowing ratios and length-to-diameter ratios. Scalar field transportation features are also investigated to clarify how different vortex structures affect the temperature distribution and the film cooling effectiveness.