Drag measurement and dynamic simulation of Martian wind-driven sensor platform concepts

The purpose of this work is to (a) determine the drag coefficient of three wind-driven systems (referred to as tumbleweeds) in a simulated Martian atmospheric boundary layer; two concepts from NASA Langley (LaRC) and one from Texas Tech University (TTU), and (b) perform a dynamic analysis of the TTU tumbleweed to establish the feasibility of operation in a simulated Martian environment. The TTU Wind Tunnel is used in order to determine the drag coefficient for the tumbleweeds in both the aerodynamic and atmospheric boundary layer (ABL) test sections. A comparison of the two mean drag coefficients for each tumbleweed model reveals the extent to which an ABL affects drag on the models. 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 ABL tests is important. It is generally accepted that a complete ABL test under conditions of neutral atmospheric stability requires knowledge of the incoming (approach) mean velocity and turbulent intensity profile, spectral distribution, roughness height, and Reynolds number. Given the fact that limited data exists for the Martian flows, physical simulations of an atmospheric surface layer with knowledge of the mean velocity and general turbulence characteristics was developed in order to obtain drag coefficients for several tumbleweed wind platform designs. The tumbleweeds drag coefficients were effectively constant with the boundary layer affected coefficient less than the respective aerodynamically obtained coefficient. Of particular interest in this study is the TTU tumbleweed, which underwent extensive testing in order to obtain a force function to describe its aerodynamic characteristics in any orientation relative to the wind.