Large Eddy Simulation of Unsteady Downburst Outflow Based on Wall Jet Model

The feasibility of a large-scale experiment for downburst in a boundary layer wind tunnel was investigated. Large eddy simulation （LES） was employed to investigate the characteristics of stationary and travelling downburst using the impinging jet and wall jet methods, respectively. The velocity profiles from LES were compared with those obtained from the Wood model, the Oseguera model, the Victory model, and the classical wall jet experiment to verify the reasonableness of the two methods. Then, three time functions of the inlet velocity were used to obtain similar time series of the full-scale data. The results show that the fully-developed velocity profiles of the wall jet cohere with those of the three theoretical models and the classical wall jet experiment. When the translational velocity is 15% of the impinging jet velocity, the maximum horizontal wind speed increased by 15.8% compared to that of the stationary impinging jet, while when the velocity of co-flow is 19.2% of the wall jet velocity, the maximum horizontal wind speed increased by 16.9% compared to that of the wall jet without co-flow. The stationary downburst can be appropriately simulated using the wall jet model without co-flow, while the travelling downburst can be effectively simulated using the wall jet model with co- flow. The results from large eddy simulation （LES） and data obtained from Andrews AFB downburst are in good agreement. The unsteady characteristics of downburst outflow can be perfectly reproduced by the time functions of the velocity inlet.