Effect of model cooling on periodic transonic flow

Abstract

Experimental investigations were conducted in a small transonic intermittent tunnel on 14 and 18% thick biconvex airfoils to study the effect of model temperature on periodic transonic flows. The Reynolds number based on the model chord was in the range 0.7-0.9 x 106. Tests were conducted in the Mach number range of 0.7-0.85, and the model-to-tunnel stagnation temperature ratio range of 0.6-1.0. The models were cooled in liquid nitrogen to the required temperature before a run. The measurements included model surface mean pressure and temperatures and tunnel side wall dynamic pressures. The results showed a large effect of model temperature on mean pressure distribution and periodic buffet excitation levels. The effects observed are thought to correspond with what would happen to adiabatic flows at greatly increased Reynolds numbers. Nomenclature Cp = pressure coefficient Cpte = pressure coefficient measured at x/c =0.95 c = model chord length, mm / = frequency, Hz M = freestream Mach number MI = Mach number just upstream of the shock n = nondimensional frequency parameter, 2irfc/u p = rms pressure fluctuations, N/M2 q = kinetic pressure, N/M2 Re = Reynolds number based on model chord TW, Tad = wall and adiabatic recovery temperature, K / = times, s u - freestream velocity, m/s x,y = coordinates from the leading edge of model 5 = boundary-layer thickness