'Shift the Dip' - Aeroelastic Effects of Shock-Control Bumps on a Supercritical Airfoil in Transonic Flow

Kurzfassung

Shock control bumps (SCBs) have been shown to improve the aeroelastic stability of transonic wings by shifting the transonic dip toward higher Mach numbers and pressures. While this global benefit has been demonstrated in earlier work, the accompanying changes in the local flow response are less well documented. The present study explores this aspect through transonic wind-tunnel flutter tests on an elastically suspended OAT15A airfoil in clean and SCB configuration, combining structural and balance measurements with time-resolved pressuresensitive paint (iPSP). This combination allows the global aeroelastic response to be related to the spatially resolved unsteady surface pressure. The measured flutter boundary confirms a clear stabilizing effect of the bump: the limit-cycle-oscillation (LCO) region is reduced in extent and displaced toward higher pressures. For the heave-dominated cases examined here, both configurations show a structurally driven oscillation at essentially the same frequency, with a near stationary shock in both cases. The most noticeable difference between the two configurations is local: in the clean case the leading-edge suction region exhibits a strong, coherent unsteady pressure response to the heave motion, whereas in the bump case this forward response is markedly weaker and less coherent. The observations are consistent with a picture in which the bump reduces the unsteady pressure response of the forward suction region rather than altering the nature of the oscillation, and they offer a possible local interpretation of the observed shift of the transonic dip. The present results are based on two representative operating points and are intended as a description of the observed behavior rather than a general proof of mechanism.