Excitation of wave packets and random disturbances in a boundary layer

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Virginia Polytechnic Institute and State University

A study on the behaviour of wave-packets and random disturbances, introduced by the vibrating-ribbon technique in a Blasius boundary layer, is presented. The experiments were conducted in the VPI & SU low turbulence wind tunnel. The flat plate model was constructed from an aluminum-paper honeycomb laminate and an aluminum leading edge with an elliptical profile.

A theoretical model was developed to verify the random and step-function-form motion of the vibrating ribbon. In the case of random disturbance introduction it was found that the random disturbances behave like infinite number, single-frequency waves and measurements of their growth made possible to verify regions of the neutral-stability curve.

In the case of wave-packet creation it was found that the wave packets behave like a structure that consists of waves of certain frequencies that grow or decay not necessarily according to the stability curve but in that way as to maintain the wave-packet structure.

Their growth as they move downstream and their quick destruction into turbulence was compared to previously published data.