Prediction of the effect of free-stream turbulence on turbulent boundary layers.

Abstract

The effect of free-stream turbulence on turbulent boundary layers is calculated using a second-moment closure which was previously shown to reproduce various turbulent flows. The numerical results are mainly compared with Hancock and Bradshaw's empirical correlation between the fractional increase in skin friction and a single parameter involving the intensity and length scale of free-stream turbulence. The model calculation well reproduces the empirical correlation unless the free-stream turbulence parameter is very large. In particular, the effect of the length scale is correctly captured in contrast to previous studies. Calculated profiles of the mean velocity and the Reynolds stress components are also in reasonable agreement with experiments. These improvements are traced to a particular generation term in the dissipation-rate transport model.