PIV measurements of intracrater flow dynamics utilizing a mound-bearing impact crater model in a refractive index matched environment

Abstract:

Impact craters are the most dominant large-scale topographic features on Mars and play a critical role in uncovering Mars’ ancient history. One particular topology of interest concerns craters hosting a central mound, the most prominent example of which is Gale Crater, which was the landing site of the NASA’s Mars Curiosity rover. Study of the sedimentary strata suggests that the crater was initially fully-filled in a once wet Martian climate and later eroded by aeolian processes to arrive at its present form. Knowledge of intracrater wind circulations is crucial in assessing the aerodynamic mechanisms that dictate the Martian sedimentary budget and impact crater evolution. These vortical circulations are formed and modified due to an interplay between vortex shedding, ambient velocity gradients, and spatial inhomogeneity of Reynolds stresses. Planar particle image velocimetry (PIV) measurements were conducted at multiple Reynolds numbers of flow over an idealized crater model in a refractive index matched (RIM) flume environment. The RIM technique acts to render the acrylic model transparent by equating its RI with that of the working fluid. In turn, this affords optical access to the interior of the crater model and minimizes laser aberrations and reflections, thus allowing near-surface measurements. Our results elucidate the dominant characteristics of intra- and extracrater flow induced by unidirectional wind. Mean flow statistics reveal four large-scale symmetric counter-rotating recirculation regions coupled with a complex dynamic of detaching and reattaching flow in the intracrater region. By collecting vector fields at two laterally offset wall-normal planes and vertically offset wall-parallel planes, we are able to infer the highly three-dimensional flow structure.