Urban Turbulence and Wind Gusts for Micro Air Vehicle Bio-inspired Designs

Abstract : We discuss the effects of wind turbulence encountered in an urban street canyon on very small unmanned aerial vehicles (UAVs) in the context of field data from the Joint Urban 2003 Experiment in Oklahoma City, OK. We present equations for the aerodynamics of such a UAV and derive equations to estimate the torque and forces encountered as a function of turbulent changes in wind velocity. We use sonic anemometer data from the experiment to compute wind velocity changes over a daylong sampling period with a temporal resolution of one tenth of a second. These changes are then used to compute resulting forces on notional UAVs of size comparable to small birds and butterflies, and for a Wasp II UAV for comparison. Computations are made for three locations using data measured near the middle of the street canyon at 1.5 and 15.7 m above ground level (AGL), as well as at 8.0 m AGL in a nearby intersection. We show graphs of turbulent kinetic energy, maximum acceleration encountered, and others. We found that accelerations greater than one gravity occur frequently, especially for the lighter vehicles, and accelerations of several gravities were common.