Effects of Wind Tunnel Disturbances on Boundary-Layer Transition with Emphasis on Radiated Noise: A Review

Abstract : Effects of wind tunnel free-stream disturbances on boundary-layer transition are reviewed. Experimental results show that free-stream disturbances dominate the transition process as determined by the experimentally measured transition Reynolds numbers on simple geometries (flat plates and sharp cones). Principal modes of disturbance are turbulence (u(tilde)/U infinity) and acoustic sound (p(tilde)/q infinity) at subsonic speeds; hole/slot acoustic resonance at transonic speeds (p(tilde)/q infinity); and tunnel wall turbulent-boundary layer radiated noise at supersonic-hypersonic speeds (p(tilde)/q infinity). Data correlations and resulting empirical equations that show the direct relationship between transition Reynolds numbers and free-stream disturbance levels are presented and discussed.