On the Effect of Free-Stream Turbulence on the Structure of Turbulent Wake

Abstract

With a view to clarifying the effect of free-stream turbulence on the structure of a turbulent wake, hot-wire experiments were carried out in the wake behind a circular cylinder of 1-millimeter diameter in an air stream of velocity 10 meters per second. The measurements were made for the two cases; the one when the free stream was undisturbed and the other when it was disturbed by inserting a grid in such a way that the resulting turbulence was of the scale comparable to the width of wake.Determinations were made of the mean velocity U and quantities pertinent to the velocity fluctuations such as u2, (∂u/∂x)2, u4 and uv. It was found that the effect of free-stream turbulence increased the turbulent intensity in the wake. Moreover, the structure of large eddies responsible for uv and u4 appeared to be scarcely affected, while that of small eddies pertinent to (∂u/∂x)2 noticeably affected at far distances downstream. These circumstances seem to suggest the rapid approach of large eddies toward a structural equilibrium.