Large Eddy Simulations of mixing in an impinging jet

The mixing characteristics of different sub grid scale (SGS) models were investigated using Large Eddy Simulations (LES) of a circular jet (Re=11000) impinging on a fiat plate. The unsteady spatially filtered incompressible Navier-Stokes equations were solved together with a transport equation for the concentration of an inert additive using a multi-grid finite difference code with a staggered grid. The un-resolved scales of the flow were modelled by a Scale Similarity Model (SSM) and a Dynamic Divergence Model (DDM). The sub grid scale mixing was modelled using a scale similarity approach (CSSM) as well as implicitly through the truncation errors of the discretisationi for the passive scalar. Spreading angle, average profile, mean fluctuation intensity and pdf-functions for the additive were calculated and compared with implicit LES and PLIF measurements. Our results show that the inclusion of explicit SGS models gives approximately the same increase in spreading angle close to the wall as a refinement of the grid in the implicit case, about 1 degrees - 3 degrees. All Sub Grid Scale models show improved results as compared to implicit LES at the same grid resolution.