Instability threshold of vehicles in floodwaters based on CFD

Abstract

[Objective] The surface flood pathway is a critical component of major drainage system. To ensure the safety and stability of vehicles when the road plays the role of drainage path, [Methods] Audi A4L was selected as the research object. The optimal Latin hypercube design was used to select the flow velocity and water depth of the flood. The VOF method and CFD numerical simulation are used to calculate the flow force on the vehicle and analyze the change of the free water level near the vehicle body, so as to reveal the instability mechanism of the vehicle under different flow conditions.[Results] The result show that the drag force and buoyancy of the vehicle are affected by the water depth and velocity at the same time. The value of the drag coefficient is stable within a certain range, and the buoyancy of the vehicle is significantly affected by the drastic change of the free surface height of the water flow.[Conclusion] When the flow velocity is less than 1 m/s, the threshold of instability water depth is 0.4 m; When the flow velocity is between 1 m/s and 4.5 m/s, and the friction coefficient is 0.25 or 0.35, the threshold of instability water depth can be expressed as a cubic function of the flow velocity; When the flow velocity is 4.5 m/s, the threshold of instability depth is 0.24 m(μ=0.25) and 0.27 m(μ=0.35). The area below the curve of the most unfavorable instability threshold is the safe zone, and the area between the two curves is defined as the instability risk area. Research result can provide reference for the risk assessment of vehicle instability in the roadway drainage path.

Keywords

floodwaters / vehicle stability / instability threshold / flow force / CFD / numerical simulation / flood forecasting / urban waterlogging