Management of a Stronger Wall Jet by a Pair of Streamwise Vortex. Production Terms in the Vorticity Transport Equations.

Abstract

Evolution and interaction processes of the three mean vorticity components were investigated experimentally by evaluating production terms in the vorticity transport equations. The measurement was made in a stronger wall jet managed by two kinds of streamwise vortex pair, namely, common-flow up and common-flow down. It is discussed that contribution of the production terms on the evolution of the mean vorticity and differences in the results between the two kinds of vortex pair. The production term expressed by product of mean vorticity and velocity gradient can be understood as the reorientation between the spanwise and vertical vorticity components under existence of the streamwise vorticity. The reorientation mechanism produces negative mean velocity gradient ∂U/∂y intensifying the large-scale eddies in the outer layer of stronger wall jet. Magnitude of the produced negative mean velocity gradient ∂U/∂y is larger in common-flow up case in which the streamwise vortex holds relatively round shape, that is, smaller ratio of spanwise radius and vertical one.