Turbulence Simulation for Wind Tunnel Testing of a Fixed-Wing Unmanned Aerial Vehicle

Abstract: Small fixed-wing Unmanned Aerial Vehicles (UAVs) usually fly at low altitudes within the atmospheric boundary layer, characterized by random continuous turbulence. To investigate the unsteady aerodynamic behavior of a flying UAV, it is necessary to simulate the fluctuations in flows as seen by the UAV, i.e., to simulate the relative turbulence spectra, particularly in the vertical direction due to its significance in changing the instantaneous angle of attack. Therefore, this study aims to replicate the turbulence spectrum of the vertical velocity component as seen by a flying UAV in the wind tunnel using an active grid. The Kaimal neutral atmospheric spectrum at a fixed point is adopted. The modified vertical airspeed spectrum, as seen by a flying UAV moving through the wind field at its flying speed at multiple flying conditions, is determined and is the target spectrum to simulate. The motor controlling the active grid is programmed with random motions so that the vertical velocity spectrum generated at the unmanned aircraft location closely matches the above target spectrum. The results show that the vertical velocity spectrum generated in the wind tunnel agrees with the target spectrum and the turbulence intensity is well matched. Keywords: turbulence simulation, unmanned aerial vehicles, wind tunnel testing, neutral atmospheric spectra, vertical dynamic response, active grid