INFLUENCE OF FREE-STREAM TURBULENCE ON CHARACTERISTICS OF A TURBULENT BOUNDARY LAYER

Abstract

The characteristics of -a turbulent boundary layer forming on a smooth flat plate have been studied in detail in the past but essentially for a very low level of tur-bulence in the free-stream. Some studies have also been carried out in the past concerning the effect of free-stream turbulence on the growth of boundary layer. These studies, however, were confined to the effect of intensity of turbulence in the free-stream and the effect of the scale of turbulence has not been studied. Hence a wind tunnel study was undertaken in the labora-tory with the intention of studying the characteristics of a turbulent boundary layer forming on a flat plate in streams of varying levels and scales of turbulence. The variations in velocity profiles, nominal, displace-men and momentum thicknesses of boundary layer and the skin-friction coefficient for various intensities and scales of free-stream turbulence have been studied. On the basis of above study the following main conclusions have been drawn : (1) The velocity distribution in the outer region of the boundary layer is relatively nsensitive-to the turbulence intensity-but is strongly affected by the scale of turbulence.