Receptivity and Transient Growth of Roughness-Induced Disturbances

Abstract

Receptivity of transient disturbances to surface roughness is a complicated phenomenon that governs both initial disturbance amplitudes and features of the disturbances’ growth and decay throughout the boundary layer. The experiments described here use hotwire measurements in a Blasius boundary layer to obtain detailed information on the initial disturbances generated by a spanwise-periodic array of roughness elements and the transient growth that follows the initial disturbances. The results indicate that disturbance energy associated with the roughness-induced disturbances scales with the roughness-based Reynolds number, Rek, for values as high as 119. At Rek 162 there is some preliminary evidence for nonlinear amplitude saturation, but this requires more complete verification.