Evolution and Breakdown of a Wave Packet Propagating in a Laminar Boundary Layer.

摘要

The program of work contained in the proposal covered a number of associated topics concerned with the evolution of instability waves and associated topics concerned with the evolution of instability waves in laminar flows, their subsequent amplification and their eventual breakdown into turbulence. Initial emphasis was placed on the non-linear growth of wave packets, following the observation that marked non-linear behavior occurred at surprisingly low signal levels. The Reynolds stresses controlling these events arise mainly from the modulation envelope of the wavetrain, and are consequently important in the types of deeply modulated wavetrain that are generated naturally by free-stream turbulence. It is intended to document this behaviour so that quantitative assessment can be made. Experiments with the addition of controlled excitation noise are in progress. The main effort on the theoretical front has been put on the question of the 'receptivity' of the laminar boundary layer to free-stream disturbances. Great Britain. (edc)