Intercomparison of calculation models for wind-driven rain on buildings

Three different calculation models for wind-driven rain (WDR) on buildings are compared by
applying them to four idealised, isolated building configurations. The three models are the semiempirical model in the European Standard Draft for WDR assessment (ESD), the semi-empirical
model by Straube and Burnett (SB) and the CFD model by Choi. The buildings are a low-rise
cubic building, a low-rise wide building, a high-rise wide building and a tower building. The
calculations are made for steady-state conditions of wind and rain. Validation of the CFD wind
flow simulations and of the WDR simulations was performed in earlier studies. The CFD
simulations of the WDR coefficient are considered as the reference case, and the performance of
the two semi-empirical models is evaluated by comparison with these CFD results based on two
criteria: (1) the ability to model the wind-blocking effect on the WDR coefficient; and (2) the
ability to model the variation of the WDR coefficient with horizontal rainfall intensity Rh. It is
shown that the ESD and SB model, as opposed to the CFD model, can not reproduce the windblocking effect. In addition, the ESD model provides WDR coefficients that are independent of
Rh, while the SB model shows a dependency that is opposite to that by CFD. Future
improvements to semi-empirical models should take into account these rather fundamental
differences.