Transition control of instability waves over an acoustically excitedflexible surface

Experimental results are presented that demonstrate the coupling of a laminar boundary-layer flow with a typical flexible aircraft panel. It is shown that the boundary layer induces plate oscillations that, in turn, perturb the flow at the same frequencies. This feedback mechanism is an inherent property of laminar boundary-layer flow passing over a flexible plate. As a result, the flexibility of the plate becomes a source of early transition. The laminar boundary layer at the leading edge of the plate reacts to small unsteady disturbances from upstream due to a streamwise pressure gradient. The experiments demonstrate that a nominal sound pressure incident at the leading edge triggers early transition. It is shown that this transition can be delayed by activating a heat source at the leading edge of the plate, which results in downstream cooling.