Study On The Influence Characteristics Of Building Facade Opening On Wind-driven Rain

Wind-driven rain（WDR）is a natural phenomenon that raindrops in the process of vertical fall are dragged by horizontal wind to obtain horizontal velocity,and at the same time fall diagonally under the action of their own gravity.It is one of the main moisture sources of building facades and directly affects the durability of buildings.For example,after the raindrops hit the building facade,they adhere to accumulate and penetrate into the interior.It is easy to cause freeze-thaw damage,water seepage erosion,weathering,fading and even cracking of the wall.The wall moisture also constitutes an important boundary affecting the thermal and humidity performance of the building.At present,the domestic and foreign existing WDR research mainly on the enclosed building,and there are few researches on WDR of open-hole buildings with large openings.When building with larger hole,with the wind field flow exist significant differences in the enclosed building,inevitably affect WDR catch ratio and distribution characteristics of the facade,especially in open hole construction form of the hole and open hole rate changes,the wind field,the influence of different level will be generated to rain trajectory change.In addition,when there is a hole,rainwater is also easy to enter the building through the hole driven by wind,which will have an impact on the inside of the building and even cause damage.In this paper,Fluent UDF programming was used to realize the simulation of WDR based on Euler Multiphase（EM）Model,and CFD method was verified according to the building WDR data measured by Kubilay et al in 2014.On the basis of showing the effectiveness of the method,WDR simulation analysis is carried out for typical single buildings with openings and series layout buildings:（1）For isolated single buildings with openings,the influences of openings form,opening rate,wind speed and rain intensity on WDR distribution of buildings are studied,and compared with closed buildings.（2）In the serial layout,WDR distribution of the windward facade of rear building was analyzed when the building spacing,wind speed,rain intensity and the size of the opening of the front building were changed under two conditions:whether the front building had holes or not.The results show that:（1）the presence of openings increases the catch ratio of windward facades,especially at the edge of openings,and the increase degree is related to the shape of openings;With the increase of the size of openings and wind speed,the catch ratio of windward facade and indoor ground of building with openings increases significantly.When the rain intensity changes around the light rain intensity,the catch ratio of windward facade and indoor ground of the open-hole building has no obvious change.When the rain intensity increases to 20mm/h,the catch ratio of windward facade and indoor ground of the open-hole building will decrease significantly.（2）In the tandem layout,with the increase of building spacing,the maximum catch ratio of windward facade of the rear buildings increases gradually when the front buildings have openings,while the maximum catch ratio of windward facade of the rear buildings decreases gradually when the front buildings have no openings.With the increase of opening rate of front buildings,the maximum catch ratio of windward facade of back buildings has little difference,which is smaller than that of front buildings without opening rate,and the difference is about 0.5.As the wind speed increases,the maximum catch ratio of windward facade of the rear building increases regardless of whether the opening is set.When the wind speed is at U₁₀=5 m/s and rain intensity is around 5 mm/h-10 mm/h,the catch ratio of windward facade of the rear building changes slightly regardless of whether the opening is set.When the rain intensity increases to 20 mm/h,the maximum catch ratio of windward facade of rear building decreased obviously.