On the effects of freestream turbulence on a small drone propeller aerodynamics and aeroacoustics.

This study investigates how turbulence affects the sound generated by propellers operating at low Reynolds number, combining both analytical and experimental approaches. Initially, incoming turbulence is analyzed using experimental data obtained via Particle Image Velocimetry (PIV) and Hot-Wire Anemometry (HWA). Additionally, oil-flow measurements were conducted. These experiments were conducted in the TU Delft A- tunnel, where acoustic measurements were also taken using a microphone arc. Turbulence is generated by means of a grid, and its statistical properties, such as the turbulence intensity and the integral length scale, are examined. A comparison is made between these properties in scenarios with and without the propeller. Subsequently, the turbulence statistics serve as input to an analytical noise-prediction model. This model predicts the power spectral density of the broadband noise emitted by the propeller when observed from a far-field position. Finally, the experimental spectrum obtained from microphone data is compared with the spectra predicted by the model.