Similarity of a wall jet with a uniform external stream and tangential suction

Abstract

The two-dimensional turbulent wall jet in the presence of an external stream and downstream tangential suction at zero and adverse pressure gradients were experimentally studied. Hot wire measurements of streamwise mean velocity distributions show that the outer regions of the velocity profiles are practically self similar for wall jets with external streams with or without suction for the ratio of the maximum local and external stream velocities U ∞/Um ≤ 0.8. Self-similarity is lacking however in the inner region, particularly very near the wall. This fact is similarly reflected in the turbulence intensity distributions and is likely due to viscous friction at the wall causing a lack of flow equilibrium. While the effect of downstream suction is negligible on the mean velocity profiles, the turbulent intensity profiles show that such suction reduces the turbulence level of the flow even far upstream of the suction slot with zero pressure gradient. An adverse pressure gradient however inhibits this stabilizing effect of suction. The adverse pressure gradient also has a similar effect to increasing the jet Reynolds number with regards to producing better data collapse when scaled appropriately. This means that both of these factors have the effect of creating a flow nearer equilibrium and thus attain a higher level of self-similarity. Copyright © 2008 by the authors.