Response of the boundary layer developing over a blunt-nosed flat plate tofree-stream non-uniformities

The response of the boundary layer on a flat plate with blunt nose to infin itesimally small non-uniformity in the freestream velocity along the span h as been studied. The non-uniformity was shown to excite boundary-layer dist urbances similar to streaks or Klebanoff modes generally observed in experi ments conducted with a high level of free-stream turbulence. The boundary l ayer disturbances have a predominantly streamwise velocity component and ex hibit transient growth. In contrast to streaks generated by streamwise vort ices impinging on the sharp nose of a plate, the disturbances produced by f ree-stream non-uniformity interaction with a blunt nose have a different le vel of growth. Their maximal amplification scales with the Reynolds number, based on the size of nose bluntness and is almost independent of the spanw ise period of disturbances. This difference was shown to be caused by addit ional amplification of disturbances via vortex lines stretching around the leading edge. (C) 2001 Editions scientifiques et medicales Elsevier SAS.