Title

Infuence Of Free-Stream Turbulence On Boundary Layers

Document Type

Report

Report Number

ARC-12397

Funder

National Aeronautics and Space Administration (NASA)

Publication Date

6-1-1992

First Page

1

Last Page

55

Abstract

The influence of near isotropic free-stream turbulence on the shape factors and skin friction coefficients of turbulent boundary layers is presented for the cases of zero and mild adverse pressure gradients. With free- stream turbulence, improved fluid mixing occurs in boundary layers with adverse pressure gradients relative to the zero pressure gradient condition, with the same free-stream turbulence intensity and length scale. Stronger boundary layers with lower shape factors occur as a result of a lower ratio of the integral scale of turbulence to the boundary layer thickness, and to vortex stretching of the turbulent eddies in the free-stream, both of which act to improve the transmission of momentum from the free-stream to the boundary layers.