Simulation of wind-driven-rain around a building

The weather resistance design of building facades requires adequate knowledge on the wind and rain environments around the building. In the present paper a numerical method for the simulation of wind-driven-rain around a building is proposed. The model involves two components. Flow around the building is computed by solving the k-ϵ two equation turbulence model. Movements of raindrops in the wind field are calculated by considering the forces acting on the droplets. Raindrop trajectories are then calculated by solving the equations of motion. Wind-driven-rain around rectangular buildings of different aspect ratios are investigated. Raindrops trajectories for droplets of different sizes are calculated. Their velocities and directions of impingement on various locations of the building are computed. The amount of rain water and its intensity falling onto different parts of the building surface are obtained. The effects of wind speed, rainfall intensity and building geometry on wind-driven-rain are investigated. It is observed that the movements of the smaller raindrops (less than 1mm) are strongly influenced by the local flow around the building. For wide buildings, they are swept upwards over the top of the front face at an angle of more than 45 degrees to the horizontal. The amount of rain water hitting the front face is observed to be strongly influenced by the wind speed. For the same building geometry, the average rain intensity on the front face for wind speed of 20 m/s is 10 times that for 5 m/s. Different locations on the faces of the building also received very different amount of rainfall. The upper quarter of the front face received much more rainfall than the sum of the remaining three quarters.