Experimental Studies on the Stability of the Transonic Flow past Airfoils

抄録

Local flow fluctuations near the airfoil surface have been measured in the speed range near critical Mach number, by using a Mach-Zehnder interferometer and a rotating-drum camera. Airfoils tested are Tomotika-Tamada airfoil, NACA-0012 and 10 per cent thick elliptic cylinder. Experiments show that amplitude and frequency of oscillation that appears when the local sonic speed is exceeded on the surface depend on the shape of the profile. In the cases of T.T.- and 0012-airfoils, the oscillation is of small amplitude and high frequency when the maximum local Mach number on the surface is not much above unity, and the time-mean pressure distribution on the surface is smooth and shows no appreciable distortion due to shock waves. In the case of the elliptic cylinder, slow oscillation of large amplitude involving distinct shock waves appears, as soon as sonic speed is exceeded on the surface.