Oscillatory shock motion caused by transonic shock boundary-layer interaction

Unsteady pressure data were obtained on a supercritical airfoil tested in the high-Reynolds-number Two-Dimensional Test Facility of the National Aeronautical Establishment (Canada). The airfoil was the BGK No. 1 with the design Mach number and the lift coefficient of 0.75 and 0.63, respectively. Unsteady pressure data were obtained from 16 fast-response miniature transducers installed on the upper surface of the airfoil. The results of data analysis disclosed discrete frequency shock-wave oscillations for certain flow conditions beyond the buffet onset boundary. The time it took a disturbance to propagate from the shock to the trailing edge plus the additional time it took for an upstream traveling wave generated at the trailing edge to reach the shock agreed quite closely with the period of shock oscillation measured from unsteady force spectra. The results support the proposed mechanism of self-sustained shock motion observed in transonic shock boundary-layer interaction. (I.S.)