Drag measurement and dynamic simulation of martian wind driven sensor platform concepts

The purpose of this work is to determine the drag coefficient of three tumbleweed concept models in a simulated Martian atmospheric boundary layer; two concepts from NASA Langley (LaRC) and one from Texas Tech University (TTU). The TTU Atmospheric Boundary Layer (ABL) Wind Tunnel is used in order to determine the drag coefficient for the tumbleweeds in both the aerodynamic and ABL test sections. A comparison of the two drag coefficients for each tumbleweed model reveals the extent to which an atmospheric boundary layer affects drag. It appears that no transformation exists that can be used to transform aerodynamic-based drag coefficients into boundary layer-based drag coefficients; therefore, reliance upon atmospheric boundary layer tests is important. It is generally accepted that a complete atmospheric boundary layer test under conditions of neutral stability requires knowledge of the incoming (approach) mean velocity and turbulent intensity profile, roughness height, and Reynolds number. Given the fact that limited data exists for the Martian surface flows, the mean velocity and roughness height are extracted from log-law profile provided in the literature. Of particular interest in this study is the Texas Tech Tumbleweed, which underwent extensive testing in order to obtain a force function to describe its aerodynamic characteristics in any orientation relative to the wind. This information was then be used in a dynamic model intended to provide a predictive tool in determining the mobility of the sensor platform in a simulated Martian environment.