Numerical simulations are employed to investigate the macro-flow dynamics and scale (Reynolds number) dependency of impinging jets with applications to downburst related high intensity winds. The flow is quasi-periodic with vortex rings, generated by the initial jet instability, impinging on the surface where they determine an unsteady separation-reattachment of the boundary layer. The maximum velocities are encountered at less than 0.05 jet diameters from the surface immediately after the touch down of the main ring-vortex. Due to the unstable separation-reattachment of the boundary layer the flow is Reynolds number (scale) dependent. The maximum in the mean velocity profiles increases and tends towards the wall as the Reynolds number increases. The unsteady Reynolds Averaged Navier-Stokes simulations provide time series which when fitted to the RFD full-scale data, (Gast, K.D., Schroeder, J.L., 2005. Extreme wind events observed in the 2002 thunderstorm outflow experiment. In: Proceedings of the 10th Americas Conference on Wind Engineering (10 ACWE), Baton Rouge, LA, USA), are used to estimate both the length and the velocity scales of the full-scale event. Moreover, these simulations provide a first spatio-temporal flow model for wind loading on structures due to downbursts. (c) 2006 Elsevier Ltd. All rights reserved.
