A revised empirical model and CFD simulations for 3D axisymmetric steady-state flows of downbursts and impinging jets

It has been recognized that downburst wind accounts for a high proportion in annual extreme winds. Although real downburst wind characteristics are complicated and far from fully understood, simplified analytical and empirical models are useful tools in wind-resistant design of structures in areas where extreme winds are dominated by downbursts. This paper aims to establish a simple empirical model with improved accuracy for 3D axisymmetric steady-state velocity fields of downbursts and impinging jets. The original OBV model (Oseguera and Bowles, 1988; Vicroy, 1991) considers the boundary layer effects by shaping functions only and the development of boundary layer is regarded as a linear variation. However, the boundary layer thickness of downbursts and impinging jets grows nonlinearly. The revised model developed in this paper integrates the nonlinear effects by incorporating varying characteristic lengths into the velocity shaping functions and adds external shaping functions for intensity scalars. Besides, based on in-depth analysis of the intrinsic properties of the shaping functions, a simple vertical shaping function of radial velocity and a modification to radial shaping function of radial velocity are proposed to improve the simplicity and accuracy of the model. A detailed 3D CFD simulation study using Reynolds Stress Model (RSM) is performed for the fitting and verification of the revised model. Compared with the original OBV model, the revised model yields more accurate steady-state flow fields especially for radial velocity profiles.