Volumetric Force Analysis Around a Free-Flying Quadcopter Using Shake-the-Box Lagrangian Particle Tracking Data

Abstract

This thesis focuses on the volumetric force analysis around a free-flying DJI Mavic 2 quadcopter using Shake-The-Box particle tracking and the FlowFit3 data assimilation algorithm to obtain continuous flow field data. By comparing the resulting thrust with the known mass of the drone, the flow fields were validated for correctness. The analysis builds on previous thrust analysis carried out by the German Aerospace Center and aims to improve on observed anomalies such as offsets in the time-averaged thrust and oscillating instantaneous thrust values for each time step. To improve the analysis, pressure was included in the equations and particle acceleration was used directly rather than relying on velocity data in the Eulerian frame. The availability of spatial data for the entire flow around the drone allowed the use of volumetric integrals to further analyse the acceleration and velocity data spatially. It was found that the inclusion of pressure dampened the oscillations as the pressure is accounting for local unsteady pressure gradients convecting downstream across control volume boundaries. However, the mean thrust offset was not improved due to false mean pressure gradients caused by yet unsolved convergence problems identified in the non-linear FlowFit3. This problem also caused errors in the reconstructed acceleration fields, making it not yet possible to use direct particle acceleration to calculate thrust. Additionally, it was discovered that pressure fields cannot be uniquely reconstructed from velocity and acceleration data when unknown external forces are present within the flow. Despite these challenges, the use of volumetric velocity data demonstrated improved reconstruction capabilities of the non-linear FlowFit3 over simple binning of particle data, especially in regions of low tracking density. These results contribute to the further development of FlowFit3 and provide a basis for future non-intrusive three-dimensional force analysis techniques in the study of aerodynamic interactions around various objects.