The resonant interaction of disturbances at laminar-turbulent transition in a boundary layer

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Abstract
The three-dimensional resonant interaction of a plane Tollmien-Schlichting wave, having a frequencyf1, with a pair of oblique waves having frequencies ½f1, was observed and studied experimentally. In the initial stages, the interaction proved to be a parametric resonance, resulting in the amplification of small random priming (background) oscillations of frequency ½f1, and of a packet of low-frequency oscillations. The resonant interaction of waves in a boundary layer was investigated also by introducing a priming oscillation with frequencyf’ = ½f1+ Δffor different values of the frequency detuning Δf. The importance of the discovered wave interaction in boundary-layer transition is demonstrated. Causes of realization of different types of laminar-flow breakdown are discussed.