Crater Evolution Due to a Jet Impinging on a Bed of Loose Particles

We investigate by means of laboratory experiments crater evolution in a bed of loose particles caused by an impinging subsonic jet. Attending physical considerations, which may apply to rocket-propelled vehicles during landing and take-off operations, are based on a simple force balance between the fluid forces and particle weight and account for the effects of bed permeability on cratering. Three bed materials were used with mean diameter ranging from 134-μm to 6-mm and particle density ranging from 0.9 g cm–3 to 2.65 g cm–3. We show that the equilibrium crater depth is weakly influenced by permeability of the bed material and introduce a Reynolds number, based on bed permeability, which captures this effect. Finally, we provide an empirical means to the estimate the maximum crater sidewall slopes and evolving crater depth as a function of jet strength.