Effect of noise on roughness-induced boundary-layer transition for scramjet inlet

Boundary-layer transition was studied on an axisymmetric scramjet-inlet mod el with compression corners, using the Purdue Mach 4 quiet-flow Ludwieg tub e. Although the Reynolds number was not large enough to achieve natural tra nsition under quiet-flow conditions on the smooth model, transition was inv estigated by applying isolated roughness elements near the nose of the mode l. Surface hot-film measurements were obtained under both quiet and noisy w ind-tunnel conditions. Both the noisy tunnel flow and the roughness element s generated intermittency in the boundary layer. The effect of the tunnel n oise was comparable to the effect of the roughness. The change from quiet t o noisy flow also changes the character of the intermittency and the effect s or the roughness, which suggests that ground tests for boundary-layer tra nsition should be interpreted with care. These results form the first subst antial quiet-flow measurements available in the open literature for superso nic boundary-layer transition over compression corners.