Abstract
Experimental and numerical results of a propeller of 0.3 m diameter operated in quiescent standard ambient conditions at 5000 RPM and axial velocity ranging from 0 to 20 m/s and advance ratio ranging from 0 to 0.8 are presented as a preliminary step towards the definition of a benchmark configuration for low Reynolds number propeller aeroacoustics. The corresponding rotational tip Mach number is 0.231 and the Reynolds number based on the blade sectional chord and flow velocity in the whole radial and operational domain ranges from about 54000 to 106000. Force and noise measurements carried out in a low-speed semi-anechoic wind-tunnel are compared with scale-resolved CFD and low-fidelity numerical results. Results identify the experimental and numerical challenges of the benchmark and the relevance of fundamental research questions related to transition and other low Reynolds number effects.
Highlights
The development of tools for the design and optimization of propellers employed in multicopter unmanned air vehicles and drones has to face two major difficulties
Recent attempts to validate Lattice-Boltzmann Method / Very Large Eddy Simulation (LBM/VLES) results [1] revealed that the flow recirculation induced by a rotor operated in a confined environment, and the consequent interaction between blades and turbulent eddies, generates high-order Blade-Passing Frequency (BPF) loading noise harmonics
Other sources of experimental uncertainties are: (i) the vibration of the test rig resulting in additional sources related to the random blade motion [3], (ii) the presence of electric motor noise, which is affected by the rotor torque [4] and not separable from the rotor aerodynamic noise, or treatable as a background noise contribution, and (iii) the flow regime at several radial stations and the presence of laminar separation bubbles
Summary
The development of tools for the design and optimization of propellers employed in multicopter unmanned air vehicles and drones has to face two major difficulties. Experimental and numerical results of a propeller of 0.3 m diameter operated in quiescent standard ambient conditions at 5000 RPM and axial velocity ranging from 0 to 20 m/s and advance ratio ranging from 0 to 0.8 are presented as a preliminary step towards the definition of a benchmark configuration for low Reynolds number propeller aeroacoustics.
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