Large eddy simulation of the proximal region of a spatially developing circular jet

Abstract

Large eddy simulations (LES) of spatially developing circular jets were carried out. The subgrid scale (SGS) model was of a dynamic type and was based on an assumed asymptotic behaviour of the SGS-stress. This assumption is valid only for adequate spatial and temporal resolutions. The effects of the SGS-model were studied by comparing simulations with and without SGS-model. LES with different spatial resolutions were performed to study the effects of the spatial resolution on the numerical solution. The numerical results were compared with experimental data. Simulations were performed for the Reynolds numbers 1⋅104, 5⋅104 and 50⋅104 to study the Reynolds numbers effects in the proximal region of the jet. The turbulent intensity increases from a low initial level, given by a low amplitude white noise disturbance in the inlet, to a high level in the studied proximal region of the jet. For the lower Reynolds numbers certain amplified frequencies were found, at Strouhal numbers about 0.3 and the corresponding first two harmonics, which agree well with experimental observations. The spatial resolution was found to be adequate to support the longitudinal and transversal Taylor length scales. A new bound for the dynamic model parameter is proposed and it is studied a priori using the computed flow fields. This bound is based on the non-negativity of the total dissipation, i.e. an entropy condition for the sum of viscous-, SGS- and numerical- dissipation, in the discrete transport equation of the resolved scale-energy.