Research on winddriven rain CFD simulation and method calculating mean rain load

Based on harmonic wave superimposing method and Kaimal spectral，the time history of fluctuating wind in open site was generated and then used as the velocity inlet for CFD flow field simulation. Fluctuating wind field and raindrops were respectively simulated by detached eddy model and discrete phase model. Using windrain coupling CFD model, hitting velocity and time of raindrops at different heights of transmission towers can be obtained. According to the impulse theorem and the impulse equivalence principle, a method for calculating rain load averaged over any time interval was proposed. Take a 176m high transmission tower as case, rain load averaged over 0.25s was calculated. The influence of horizontal wind speed and rain intensity on mean rain load are as follows: horizontal mean rain load increases with wind speed and rain intensity, while the ration of rain load to wind load decreases with the increment of height. Although single raindrops can induce considerable rain load, this load would last only about 10 -5s. Thus, rain load averaged over a certain time interval is rather small by use of the impulse equivalence principle. For the case of a 176m high transmission tower, the ration of mean rain load to mean wind load is no more than 2.6%