Large-eddy simulation of impinging jets with embedded azimuthal vortices

摘要: We have carried out large-eddy simulations of an impinging jet with embedded azimuthal vortices, a model the wake helicopter hovering in ground effect. The vortices are generated by sinusoidal forcing velocity at exit. They strengthen while they advected towards ground; when close to solid surface, layer opposite-sign vorticity is formed wall, and lifted up form secondary vortex that interacts primary one. Regions reversed flow caused strong, localised, adverse pressure gradient. After this interaction, begin decay, mostly due Reynolds shear stresses, which contribute turbulent diffusion term budget phase-averaged vorticity. This mechanism extremely robust, plays most important role decay even if no turbulence initially present jet, or no-slip condition removed. A three-dimensional instability a...