Turbulence control in wall jets

A new method for the control of mixing of a plane turbulent wall jet has be en investigated. A thin wire, mounted in the vicinity of the wall-jet nozzl e, changes the formation of the shear-layer structures in the early stages of the development of the wall jet. The wire is operated in two ways: (1) a still wire inhibits the natural shear layer roll-up and reduces the size o f the turbulent structures and thereby the mixing; (2) a self-excited oscil lating wire introduces large coherent structures and thereby enhances the m ixing. The size of these structures does not depend on the shear-layer inst ability but rather on the wire frequency. Measurements of the mean and fluctuating velocities have been performed wit h hot-wire anemometry as well as measurements of the skin friction by means of Preston tubes, surface fences and wall hot-wires. The Reynolds number b ased on the slot width was Re-j = 10000. (C) 2000 Editions scientifiques et medicales Elsevier SAS.