Bushfire-enhanced wind load on building structures

The present thesis aims to explore the fundamental mechanisms governing the interaction between the fire-enhanced wind and residential low-rise structures, with a focus on the aerodynamic load on the roof and smoke transport. For this purpose, an immersed boundary - lattice Boltzmann method - finite difference method (IB-LBM-FDM) is developed, and applied to three scenarios at high Reynolds numbers (Re > 2.5 × 105). To address the intense computational cost of high-fidelity fire simulations, an efficient geometry-adaptive multi-block solver is developed by employing the Boussinesq approximation and the volumetric heating and smoke source models for fire and smoke modeling, respectively. The solver is specifically designed for high temperature gradient flows with ground effects using wall-modelled large eddy simulation (WM-LES) and is vali- dated against extensive numerical and experimental benchmark cases with/without a fire showing satisfactory accuracy for the scales of fire considered in this study. Chapter 3 explores the role of fire-enhanced wind on the aerodynamics of a gable roof structure and designs a bio-inspired geometry modification to reduce the roof load. The results show that the fire-enhanced wind can generate very high uplift forces on the building, about three times that of the wind-only cases. Inspired by flippers of humpback whales, scalloping the edges of the building generates strong streamwise vorticity and significantly improves the flow separation in both normal and oblique directions in both wind-only and fire-enhanced wind conditions, leading to a reduction in overall roof load. In chapter 4, the role of openings on both aerodynamics and smoke ventilation into the building during a fire event is studied. It is found that the net pressure load on the building roof increases even with a small-sized windward opening. In addition, during fire events, buildings with multiple openings allow for more smoke to penetrate compared to those with single openings. In chapter 5, a study on the effect of neighboring structures on the aerodynamics and smoke ventilation around the structures in urban-like geometries is presented. A notable increase in wind load of all buildings is found under the fire-enhanced wind condition compared to the wind-only condition. A combined vortex-entraining and vortex-trapping mechanisms are found to generate a downward flow that allows smoke to be entrained and trapped from the smoke plume in the wake of the last row of buildings.