Improved Empirical Model and Numerical Simulation of an Impinging Jet with Application to Steady-State Flows of Downbursts

Downburst events generate extreme near-surface winds over a considerable area, posing significant threats to structures. The existing empirical models usually model the vertical and radial steady-state profiles of the downburst separately based on empirical equations. However, these models are difficult to consider the effects of the nonlinear growth of boundary layer thickness, and a spatial wind velocity field encompassing the core region has yet to be established. This study proposes a novel empirical model based on a generalized modal decomposition. It features an improved vertical shaping function for the radial velocity and a set of data-based characteristic functions for the model parameters. Furthermore, the integral expression for the vertical velocity field is derived based on the mass continuity equation. Detailed computational fluid dynamics (CFD) simulations using large eddy simulation were conducted for model calibration and validation. The results demonstrate that the improved vertical shaping function significantly improves the accuracy of the simulated radial velocity, particularly in the near-wall region near the downburst center. By employing the empirical model alongside the CFD simulation data, continuous radial and vertical velocity fields in space of downbursts are constructed for the computational region. These fields show excellent agreement with the validated CFD simulations and available wind tunnel test data, indicating that the model can provide a valuable reference for wind load calculation and structural safety assessment of structures subjected to downburst winds.