From transport to deposition: Mapping snow distribution under the particle size effects

Natural snow is a heterogeneous material whose mechanical properties are significantly influenced by its varying particle size and gradation. This study systematically investigates the effects of snow particle size and gradation on roof snow distribution through integrated computational fluid dynamics (CFD) simulations and wind tunnel tests. Wind tunnel tests employing high density silica sand of three sizes to simulate snow particles were first conducted to elucidate the influence of particle size on snow distribution and validate the numerical method. Subsequent CFD simulations analyzed the effects of the coupling of wind velocity, roof span, and particle gradation with particle size on flat roof snow deposition. Through quantitative comparisons of simulation results obtained with various equivalent particle sizes, a method was ultimately developed to determine an equivalent size that effectively represents complex gradations. Results indicate that roof snow distribution is governed by the coupled effects of wind velocity and roof span with snow particle size. Higher wind velocity enhances transport, reducing snow depth for a given particle size, whereas larger particles increase depth by resisting erosion more effectively, an effect intensified under stronger winds. Concurrently, a larger roof span leads to greater snow accumulation depth by providing increased storage capacity. This expanded capacity is optimally utilized by a critical particle size of approximately 0.5 mm, with both finer and coarser particles showing reduced adaptability. The arithmetic mean diameter proves to be a superior equivalent value, as it effectively replicates the complex snow distribution obtained from full gradation analyses.