Stretching of freestream turbulence in the stagnation region

Characteristics of stretched vortices in the stagnation region, due to the presence of freestream turbulence in the incident stream, were studied by means of spatial correlation. The spanwise length scale of the stretched vortices, lm, and the characteristic height corresponding to the distance between the averaged position of the centers of the stretched vortices and the plate, H_v, are successfully correlated with the integral length scale of freestream turbulence. It is found that for each of the cases studied l_m and H_v are comparable, and l_m falls in the range of ∼ 0.61-0.81 times the integral length scale of the corresponding freestream turbulence. Thus, the mechanism of inviscid vorticity stretching is suggested responsible for the development of three-dimensional vortical structures in the stagnation region outside the viscous layer.