Boundary Layer Tripping Studies of Compressible Dynamic Stall Flow

Abstract

The challenging task of “properly” tripping the boundary layer near the leading edge of an airfoil experiencing compressible dynamic stall has been addressed. Real-time interferometry studies have been conducted on an oscillating airfoil undergoing compressible dynamic stall at free stream Mach numbers of 0.3 and 0.45, by separately placing five different trips of varying sizes. The trip heights ranged from 40pm to 175pn;the estimated boundary layer thick-ness was 60pm at the point of flow separation at a Mach number of 0.3. Quantitative analysis of the in- terferograms showed that the laminar separation buh- ble characteristic of low Reynolds number airfoil flows was still present with the smallest trip and prema- ture dynamic stall occurred with the largest trip. A roughncss element extending between 0.5% chord to 4%chord from the leadin edge and of a hei ht cam parahlc to the boundary layer thickness at &e pain; where the dynamic stall vortex forms was found to he the “right” trip.