Research On Wind-induced Non-uniform Snow Distribution On Building Roofs Using Wind Tunnel Test And Numerical Simulation

The snow particles undergo complex drift movements under the action of wind,and the aerodynamic characteristics of the building change with the uneven deposition of snow around the building and on the roof.A large number of cases have shown that the uneven deposition of snow on the roof and the aerodynamic effects caused by it have a significant impact on the safety,comfort,and durability of the large-span structure of the large public housing roofs.Building collapses caused by snow often occur in large-span structures and simple steel structures.The main contents carried out in this paper are as follows.1)The formulas of the fluid incipience and impact incipience of snow particles were deduced,and the snow distribution on the stepped roofs was stimulated by using the commonly used snow erosion test method.The limitations of the conventional method were found.Aiming at the problem that the snow erosion test method can not consider the snowfall factors and is difficult to apply to the complex roof model,the snowfall simulation test method is proposed.The distribution law of non-uniform snow load onstepped roofs under the snowfall environment is summarized.Wind tunnel tests were carried out on spherical roof models with different rise-span ratios using snowfall simulation experiments.The distribution of snow on spherical roof under different wind speeds and different rise-span ratios was obtained.2)A probability-based half-steady Eulerian-Lagrangian method was proposed to simulate snow change on a roof.The snowfall process was divided into N steady stages,and the snow boundary of each stage was updated according to the snow deposition probability on the roof in the previous stage.In the numerical simulation,the steady wind field was calculated,and then the motion of particles was calculated using the Lagrangian method.Calculation time was effectively reduced by computing the deposition probability of snow particles on the roof.This method was used to calculate snow distribution on a stepped flat roof model under different wind velocities.Results of the numerical simulation and wind tunnel test exhibited good agreement with the measured results,which accurately reproduced the typical snow distribution on the lower roof.3)A Single-Phase Steady-State(SPSS)CFD model using Immersed Boundary Method(IBM)was proposed to simulate the snow drifts development on large roofs.Flow field of wind was described under the Eulerian framework and modeled with Reynolds-averaged Navier–Stokes(RANS)equations.The movement of snow particles in the air was modeled using the Eulerian method.The snowfall process was divided into n steady stages,and the snow boundary of each stage was updated by moving the coordinates of Immersed Boundary(IB)points.This method can adapt to complex and changeable snow boundary without re-meshing.The friction velocity over snow surface can be calculated accurately using the modified model of wall shear stress proposed in this paper.Numerical simulation results were verified by field observation and wind tunnel test of snow distribution on stepped flat roof models.Good agreement between numerical simulations and experimental results of spherical shell model was achieved and the applicability of this method to curved roofs was verified.The effects of different threshold friction velocities and test durations on the snow distribution on spherical shells were also analyzed.4)Because the first two methods are difficult to apply to the simulation of snow distribution on full-scale long-span roofs.A quasi-steady state numerical strategy based on volume of fluid method(VOF)and solidification / melting(SAM)model is proposed.The roof and snow boundary are simulated by solidified liquid,and the background grid is orthogonal grid to simplify the modeling process in this method.The deposition process of snow particles on the stepped flat roof model and the pitched roof model in snowfall weather is simulated.The simulation results of snow distribution on the roofs are similar to the measured results,which verifies the feasibility of the proposed numerical method.Finally,the distribution of snow on a full-scale three span suspension roof in snowy weather is predicted.