High-resolution LES of a starting jet

Abstract An impulsively started jet is investigated by a highly resolved large-eddy simulation (LES). The numerical calculations are presented, analyzed and compared to the experimental data by Soulopoulos et al. (2014). Different inlet velocity profiles and their turbulence intensity are employed in the simulations to identify the appropriate boundary conditions by comparing the obtained mixture fraction and its dissipation rate against the experimental data. A sensitivity analysis of the numerical calculations to the different filter sizes is performed, and the ramp-up functions of the inlet flow are investigated. A satisfactory agreement between the simulation and the experiment is achieved. It is found that the potential core, which is observed in our calculations, was absent in the experiments, likely due to premature mixing in the nozzle. Two parameters, namely the mixture fraction and its dissipation rate, are chosen for the statistical evaluation, which is presented for both the calculation and the experiment. It is clear that the initial/boundary conditions influence the flow dynamics, thus considerable differences in the statistics can be observed. The comparison of the resolved scales shows that the simulation resolves structures smaller than those from the experiment by a factor of two. However, this does not lead to the discrepancy of the numerical and experimental statistics, which is independent of the resolution. It is observed that the high scalar dissipation rate (SDR) values are mainly located in the mixing layer, however the vortex ring is occupied by the considerably lower SDR values.