Aeolian Simulations: A Comparison of Numerical and Experimental Results, with Projections for Titan.

Aeolian processes are major determinants of geomorphology on bodies in the Solar System possessing an atmosphere-surface interface and transportable sediment, including Earth, Mars, Venus, and Titan. Substantial efforts have been made over the last few decades to understand these processes using specialized wind tunnels, field studies, and, more recently, numerical simulations. This thesis describes a model of aeolian sediment transport using computational fluid dynamics (CFD), and compares the results with those obtained in the Martian Surface Wind Tunnel (MARSWIT) testing conducted in the Planetary Aeolian Laboratory at NASA Ames Research Center. The ultimate goal of the thesis was to develop an experimentally validated computational approach for modeling aeolian sediment saltation on Titan and other planetary bodies.

In this thesis, sieved walnut shell particles with diameters of 175-250 microns were placed on the test section floor of the MARSWIT tunnel, the tunnel was started, and the free stream airspeed was raised to ~2.5 to 7.5 m/s. A Phantom v12 high-speed camera was used to image the resulting particle motion at 1000 frames per second, and the open source software, ImageJ, was used to evaluate particle motion.

Airflow in the MARSWIT facility was modeled with Ansys FLUENT, a commercial CFD program. Surface properties for roughness height (K_s) and roughness constant (C_s) were determined through computation of a dimensionless roughness height parameter, , while using von Kármán's constant. The turbulent scheme used in FLUENT to obtain closed-form solutions to the Navier-Stokes equations was a 1st Order Discretization, k-epsilon (two-equation) model. These methods produced computational velocity profiles that agreed with experimental data to within 10-15%. Once satisfactory modeling of the flow field had been achieved, a Discrete Phase Model (DPM) was utilized to simulate particle trajectories numerically. A Euler-Lagrangian scheme was employed, treating the particles as spheres and tracking each particle at its center. Calculated particle trajectories agreed closely with experimental results, within error bounds. Projections of Titan trajectories for specific conditions are among the major results presented and discussed and show higher and longer lofts than currently estimated.

Final copy.