I spent this evening studying some well-respected sand dune theory before my upcoming trip to the Libyan Sahara. It had been a long day, with lots of fresh air, and I may have bitten off more than I could chew. Let me share a small excerpt of it with you:
‘Confining ourselves to fully developed turbulent flow throughout the fluid, there remains the question of the small-scale flow over and round the individual grains on the surface. This depends on Reynolds’ Number of the form V*d/v, where d is the mean surface roughness which is of the order of the grain diameter. It has been found that when V*d/v>3.5 the grain behaves as an isolated obstacle in the path of the fluid, and throws off a chain of eddies from its lee face.’
From ‘The Physics of Blown Sand and Desert Dunes’ by R.A. Bagnold. 1954.
Great stuff, I’m sure, but enough to make anyone head into the wilderness.