The production of uniform shear flow in a wind tunnel

Abstract

A nearly uniform shear flow, was obtained in the working section of a wind tunnel by inserting a grid of parallel rods with varying spacing.The function of such a grid is to impose a resistance to the flow, so graded across the working section as to produce a linear variation in the total pressure at large distances downstream without introducing an appreciable gradient in static pressure near the grid. A method of calculating a suitable arrangement of the rods is described. Although this method is strictly applicable only to weakly sheared flows, an experiment made with a grid designed for a shear parameter as large as 0·45 gave results in close agreement with the theory. There was no evidence from the experiment of any large-scale secondary flow accompanying the shear–a danger inherent in an empirical attempt to grade the resistance of the grid–nor was any tendency observed for the shear to decay with increasing distance from the grid.