Laminar instability and transition on the X-51A.

摘要

A 20% scale model of the X-51A was tested in the Boeing/AFOSR Mach-6 Quiet tunnel. Freestream noise was found to have a major impact on transition on the windward and leeward vehicle surfaces. The effect of noise on transition was observed with a smooth wall and for roughness-induced transition on both surfaces.;Temperature sensitive paint (TSP) and hot wires were used to characterize transition onset on the windward surface. The transition Reynolds number (R etau) increased by a factor of at least 2.2 for a smooth wall, 2.4 with ramp roughnesses, and 1.7 for diamond roughnesses when the freestream noise was decreased.;Pressure sensors and TSP determined the presence of the second-mode instability on the lee side. Disturbances near 100 kHz were observed to grow in amplitude with both downstream distance and increasing freestream Reynolds number. At one condition, transition on the center line occurred when the the disturbance amplitude reached about 3%. Reducing noise levels increased Re tau by a factor of at least 2. Transition was not observed on the lee side at the maximum Reynolds number giving quiet flow. Computations predicted that the most unstable instability is the second-mode near 100 kHz, in good agreement with the experimental data.