Numerical investigation of flows around small-scale propellers: Possibilities and challenges

Abstract

This talk focuses on flows induced by small-scale propeller blades and the wakes shedding from their tips. Flows around propellers for unmanned air vehicles (approximately 25-75 cm in diameter) in hover are simulated by different approaches to considering turbulence. The challenges to simulating these kinds of flows mainly arise from the relatively low values of Reynolds numbers (several tens to several hundreds of thousands) when transition and other flow phenomena may be expected. The adopted numerical set-ups are validated though comparisons with available experimental data. It can be concluded that global aerodynamic performance can be determined with satisfactory accuracy (the discrepancies between computed and measured values of thrust and torque remain below several percents). However, discerning the actual flow characteristics remains challenging. Here, some distinguishing features of small Re rotational flows are accentuated and discussed. Vortex wakes shedding from the blades are visualized and analyzed. These two benchmark examples provide useful guidelines for further numerical and experimental studies of small-scale propellers.