Influence of Freestream Turbulence on Boundary-Layer Development

Abstract

The influence of the wind-tunnel turbulence on the development of a turbulent boundary was studied. The experiments were carried out in the low-turbulence wind tunnel of the DFVLR-AVA at a freestream velocity of U^ = 20 m/s. The turbulence level (Tut -0.06%) was increased up to Tuj «1% by means of various grids at different positions in the settling chamber or nozzle. For a fixed transition and constant distance from the nozzle throat, the effect of the wind-tunnel turbulence on the wall shear stress was investigated. In particular, an attempt was made to separate the effects which result from the turbulence intensity and from the turbulence structure, which is different in each wind tunnel.