Field measurement and numerical simulation on distribution characteristics of wind-driven rain in setback buildings

Under wind driven-rain (WDR) environment, building facades will absorb rainwater to varying degrees, which directly affects the heat and moisture migration of walls and the durability of wall materials. So far, the majority of research on architectural WDR has been focused on regular buildings with cubic shapes, and little research has been conducted on WDR for the widely used setback buildings. Therefore, it has become essential work in the field of WDR to reveal the spatial movement and facade distribution pattern for this type of building. In this paper, field measurements are conducted on a setback building and the WDR results are compared with traditional semi-empirical model predictions. Based on this, the Eulerian multiphase model is used to simulate the WDR field of setback buildings and analyze the influence of key factors such as wind speed, rain intensity, and shape size on the WDR flow characteristics and distribution for different typical setback buildings. The results show that, unlike the case of cubic building facades where the WDR catch ratio gradually increases along the height and is continuously distributed, the step shape of the setback building seriously disturbs the wind field and creates complex turbulence, resulting in a sudden plunge in the WDR distribution of the upper setback facade and a drastic change in the catch ratio along the height. In the simulated range of variables, the plunge rises with the increase of the upper setback facade indentation size; the plunge of the catch ratio at the base of the setback facade compared to the top of the bottom facade grows from 28.8% to 81.6% when the setback indentation size changes from 2 m to 8 m. When wind speed U-10 = 10 m/s and rain intensity R-h = 2 mm/h, the difference between the maximum and minimum values of catch ratio on the vertical midline of the upper setback facade can reach 308.2%, reducing the wind speed and rainfall intensity can lessen the difference. The field measurement results indicate that the difference between the measured mean value of WDR at the upper measurement point and the lower measurement point reaches 287.1%, which is similar to the numerical simulation, both significantly different from the traditional cubic building case. It demonstrates that the WDR field of the setback building is more complicated owing to the interference of the step profile.