Generation and manipulation of uniform shear with the use of screens

A procedure for the generation of uniformly sheared turbulent flow in the wind-tunnel using separate channels with adjustable blockage is described in detail. Measurements of the reduction of mean shear in a flow crossing transverse grids and gauzes with uniform solidities are also reported: for small flow disturbances, i.e. small relative screen element thickness, d/h, the shear reduction factor, A, was found comparable to predictions, A p; however, for d/h > 0.01, the ratio A/Ap decreased rapidly with increasing d/h. Results on the effect of screen insertion on the upstream shear and the combined effects of multiple screens are briefly discussed.