A lattice Boltzmann model for particle transport and de - positionA

(received ; accepted) PACS. 47.11+j { Computational methods in uid dynamics. PACS. 02.70Ns { Molecular dynamics and particle methods. Abstract. { Solid particles (such as snow or sand) can get eroded and transported by the wind, and little understanding has been achieved in this domain. We propose a description of the phenomenon in terms of a cellular automata and lattice Boltzmann model. Numerical simulations show that plausible mechanisms are suucient to explain a wide range of deposition patterns occurring at diierent space scales. In particular, we reproduce the so-called ripples, that is oscillations of the deposition surface for which no formation mechanism is clearly established. Introduction. { The dynamics of solid particles erosion, transport and deposition due to the action of a steaming uid plays a crucial role in sand dune formation, sedimentation problems and snow transport. This eld remains rather empirical compared to other domains of science and experts do not all agree on the mechanisms involved in these process. In what follows, we focus the discussion on the problem of snow erosion and deposition. Diverse patterns of accumulations occur 1, 2], with quite diierent characteristic sizes: they range from the small ripples (oscillations of a few centimeters over a at surface) up to large wind slabs leeward a mountain crest (tens of meters). In addition to interesting academic problems, snow transport by wind raises important practical questions that strongly innuences human activities in mountain or nordic areas: snowdrifts burying roads or buildings 3], wind slabs launching avalanches. Obstacles are built in such places so as to innuence the wind pattern and modify the deposit. But, as no forecasting tool exists, their shape and location are rather empirical 1]. Phenomenologically, snow transport (i.e. erosion and deposition) has been divided in three main processes, each corresponding to a diierent scale 1]: (i) Creeping: particles are \rolling" on the snow surface or making very little jumps; (ii)Saltation: in the rst half meter above the surface, snow particles have been observed to be ejected vertically and follow a ballistic