Unsteady Airflows and Their Impact on Small Unmanned Air Systems in Urban Environments

Existing unmanned air system platforms currently do not lend themselves well to autonomous operation within complex, highly variable aerodynamic environments. As such, there is a need for accurate high-fidelity urban airflow models to help reduce the risk of failure of urban unmanned air system surveillance and engagement missions. Although urban aerodynamics are exceptionally complicated because of complex interactions between geometry, physical conditions, and varying meteorology, high-fidelity computational fluid dynamics models exist that capture these interactions effectively. Using sufficient resolution, these large-eddy simulation models provide a viable means to characterize urban airflow environments when wind-tunnel testing and field trials are too expensive or impossible. This paper presents a simulation tool that captures unsteady aerodynamics of aircraft flight in an urban environment for the study of vehicle-environment interactions. By combining a high-resolution model of the terrain/buildings with a precomputed large-eddy simulation wind field throughout the urban environment and the closed-loop dynamics of a vehicle flying a desired trajectory, the simulation computes in real time the response of the vehicle linear and angular velocity to the unsteady wind field. The paper describes the mathematical development and implementation of several new environment-vehicle interaction models that could, through the unmanned air system simulation tool, revolutionize the understanding of these interactions in urban environments.