Combined effect of jet impingement and density perturbation forcing on the evolution of laboratory-simulated microbursts

A laboratory simulation was assessed for its capacity to reproduce the actual conditions found in a microburst. In our experimental set-up, the flow was driven by combined impinging jet and density perturbations forcing with the aim of determining their relative influence on the overall microburst behavior and, in particular, the initiation and structural evolution of the resulting vortex. These results were compared with those reported in the previous simulation works. Such comparisons showed that the laboratory model may satisfactorily reproduce relevant aspects of a microburst. An expression for the characteristic microburst propagation velocity was derived, accounting for the combined effects of forced velocity and flotation forces generated by the density difference, whose predictions are in good agreement with experimental data. The vortex structure is largely affected by the forcing type. The succession of vortex is best defined when a large density perturbation is combined with a weak jet impingement. The opposite configuration causes a main vortex to be succeeded by a wake where vortex structures are not clearly defined. Such behavior is caused by the fact that larger density perturbations inhibit the mean and turbulent velocities, favouring a well defined vortices structure, associated with weaker momentum diffusion.