Streamwise scaling of streaks in laminar boundary layers subjected to free-stream turbulence

A flat plate laminar boundary layer subjected to free-stream turbulence, generated by grids upstream of the leading edge, has been studied. Correlations between a wall wire and a hot wire in the boundary layer have been obtained. The hot wire has been traversed to 328 positions for each of the five wall-wire positions studied. The length, height, and width of the correlation distributions is seen to increase in the downstream direction being self-similar in coordinates scaled with the boundary-layer length scale. The propagation speeds of the structures are obtained from the data and its variation in the streamwise and wall-normal directions is found to agree with what is obtained from a simple kinematic model. (C) 2004 American Institute of Physics.