The High Performance of the High-Aspect-Ratio Film-Cooling Scheme
The film cooling effectiveness of a slot is ideal, but it has been rarely used, mainly because of its mechanical strength. The film cooling effectiveness of the current using geometries is far from perfect. A new advanced film cooling scheme, named high-aspect-ratio holes has been proposed. Its four configurations were designed, and numerically simulated under density ratio = 2 and varied blowing ratios. All configurations demonstrate extremely high film cooling effectiveness values, some are as high as the so-called perfect performance, while their mechanical strength are similar to the conventional schemes. The new scheme exhibits two traits distinctive from the conventional geometries: Its film cooling effectiveness is much higher than the coverage ratio (t/P), and the high film cooling effectiveness is obtained under strong counter-rotating vortex pair (CRVP). It has been found that, in the new scheme, along with the aspect ratio value increase, the CRVP move away from the coolant-mainstream interface, and the coolant laterally expands in the vicinity of the exit. Consequently, a continuous coolant film would occur near the trailing edge position if aspect ratio is high enough. The approach of high-aspect-ratio holes is proven to be a way to design the highest film cooling performance geometries.