Wind tunnel model tests of snow drifting on a two-level flat roof

Abstract Consistent similarity of the flow regime and the behaviour of individual snow particles is difficult to achieve at a reduced geometric scale. As a result, model studies of snow drifting and accumulation invariably require the relaxation of some of the similarity parameters. This paper examines drift formation on the lower level of a large-area two-level roof at different wind speeds and in two different approach terrains. In relatively rough terrains, the effective surface shear stress is determined primarily by the collective drag of various buildings and the loss of horizontal momentum during saltation is less significant. In such situations both the deposition and drifting of snow at roof level is strongly influenced by the overall aerodynamics of the building shape and its surroundings.