An investigation of snow drifting on flat roofs: Wind tunnel tests and numerical simulations

Abstract

In snowy areas, the accurate prediction of snow distributions on roofs plays an important role in designing structures. The process of snow accumulations on roofs is complicated due to the action of wind, which is related to the wind field conditions (e.g., wind velocity, turbulence intensity, and wind direction), the geometry of roofs, temperature, humidity, and the property of the snow. To systematically study the effect of the length-height ratio of the flat roof and approach flow velocity on the uneven accumulation of snow loads on 3D flat roofs, wind tunnel tests of snow drifting are carried out using silica sand to simulate snow particles. Four models are designed with length-height ratios of 1, 2, 3, and 4, and then four nominal wind velocities are taken into consideration, namely 5.0 m/s, 5.5 m/s, 6.0 m/s, and 6.5 m/s. Two newly added parameters, the snow residual rate η and the erosion rate λ, are set up to illustrate the snow redistribution on 3D flat roofs. Then the effects of wind velocity or roof length on the average transport rate and the mass flux of flat roofs are systematically analyzed. Furthermore, the flow characteristics around the flat roof are obtained by means of numerical simulation, and the relationships between the flow characteristics (vorticity magnitude and friction velocity) near the flat roof and the snow redistribution pattern are carefully discussed. The snow redistribution on flat roofs is obviously uneven due to erosion mainly on both sides where the vorticity magnitude and friction velocity are also larger than in other places. The quantitative analysis indicates that the transport rate of snowdrift on the whole flat roof is proportional to the 4.45 power of the approaching wind velocity, which is slightly larger than the 3.8 derived from the empirical formula from field measurements.