The development of a perturbed, incompressible, turbulent boundary layer

Abstract

The response of a fully-developed equilibrium turbulent boundary layer to a small disturbance was observed experimentally under low-Mach number conditions: a turbulent boundary layer in an axisymmetric channel under zero pressure gradient was perturbed by a single fence like two dimensional protuberance, and the subsequent development of the velocity profile, the turbulent-shear-stress profile, and the wall shear stress was recorded by a constant-temperature hot-wire anemometer and a Preston tube. The height of the five roughness elements used ranged from 0.011 to 0.100 inches (2-15% of the original boundary layer thickness). The perturbation effects are observable only in the vicinity of their origin and each parameter undergoes an individual recovery process. The wall shear stress exhibits a unique style in its development. A perturbed turbulent-shear-stress profile shows a maximum as in the case of a turbulent boundary layer in an adverse pressure gradient. The analysis of the data has revealed a self-preserving feature of the developing velocity profile in form for small enough disturbances: the wall region of the boundary layer is in a local equilibrium after 30 roughness-heights and the unaffected outer layer retains its original characteristics.