Reynolds Number Influence on 2-D Compressible Dynamic Stall

Abstract

Reynolds number effects on oscillating airfoil compressible dynamic stall flow have been investigated. The Reynolds number was doubled at constant Mach number by using two (untripped and tripped) NACA 0012 airfoils, one with 3-inch chord and another with 6-inch chord. Pressure distributions documented using point diffraction interferometry( PDI) are compared with each other for Mach numbers of 0.3 and 0.45 at different reduced frequencies. Comparisons with a reference data set at Re = 4 x 106 for a Mach number of 0.3 at reduced frequencies of 0.05 and 0.1 showed good agreement for the tripped 6-inch airfoil, thus establishing a minimum model Reynolds number for simulating full-scale results. Reynolds number influence manifests as an increase in the airfoil peak suction pressure coefficient, smaller laminar separation bubble, increase in dynamic stall onset angle, and an increased ability to withstand adverse pressure gradient in the flow. At lower Reynolds numbers, dynamic stall arises from the bursting of the laminar separation bubble at both M = 0.3 and 0.45. At higher effective Reynolds numbers, dynamic stall is induced by large adverse pressure gradient in the flow for M = 0.3 and shock induced dynamic stall onset for at M = 0.45.