The weather resistance design of building facades requires adequate kn
owledge on the wind and rain environments around the building. In the
present paper a numerical method for the simulation of wind-driven-rai
n around a building is proposed. The model involves two components. Fl
ow around the building is computed by solving the k-epsilon two equati
on turbulence model. Movements of raindrops in the wind field are calc
ulated by considering the forces acting on the droplets. Raindrop traj
ectories are then calculated by solving the equations of motion. Wind-
driven-rain around rectangular buildings of different aspect ratios ar
e investigated. Raindrop trajectories for droplets of different sizes
are calculated. Their velocities and directions of impingement on vari
ous locations of the building are computed. The amount of rain water a
nd its intensity falling onto different parts of the building surface
are obtained. The effects of wind speed, rainfall intensity and buildi
ng geometry on wind-driven-rain are investigated. It is observed that
the movements of the smaller raindrops (less than 1mm) are strongly in
fluenced by the local flow around the building. For wide buildings, th
ey are swept upwards over the top of the front face at an angle of mor
e 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 fr
ont face for wind speed of 20 m/s is 10 times that for 5 m/s. Differen
t 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.