Modelling fluvial flow with Ansys fluent and comparison with Martian analogue lab-scale experiments and Martian gullies

Abstract

We explore the possibility of using ANSYS’ FLUENT computational fluid dynamics software to model the flow of water down beds of fine sand, medium sand and crushed rock at both Earth and Mars ambient temperatures (293K and 253K respectively) and atmospheric pressures (1000 mBar and 7 mBar respectively). The aim of the project is twofold; firstly to test the applicability of FLUENT for modelling such systems, and secondly using it to gain insight into observed martian flow features, such as kilometre-scale gullies by up-scaling the model. The results of the modelling have been validated against a well characterised set of lab-scale experiments which showed that the flow runout distance increases with decreasing pressure and temperature due to the freezing of the water at the base of the flow. This effectively decreases the permeability of the granular bed. Careful comparison of modelled to experimental results gives us confidence in the model parameters and enables us to extend the model to include the effect of reduced martian gravity. Modelling was performed using V12.1 of FLUENT and several different 3-D model setups were investigated involving erosion (mass transport) of the bed, heat transfer between the bed and the water, and the effect of sublimation and freezing of the water. This gives a full topographical model of the bed to compare with the experimental data