Aeroacoustic and Aerodynamic Characteristics of Propeller Tip Geometries

Abstract

A series of experiments were conducted in an aeroacoustic wind tunnel facility to investigate the aerodynamic performance and noise characteristics of propellers with various modifications to its tip geometry. A baseline propeller was designed for static hover conditions. The blade was adapted with the intention to reduce, divert or eliminate the blade tip vortex which is responsible for blade vortex interaction noise. All of the propellers were fabricated using advanced additive manufacturing techniques and tested experimentally in both static hover and forward flight modes of operation. The blade thrust and torque, as well as the radiated far-field noise were collected over a range of rotational speeds in static hover and forward flight conditions. Data was also collected at a thrust-matched condition for each tip modification permitting comparison of figure of merit at static hover. Particular attention was given to the 1st blade passing frequency tone and its directivity and magnitude. Various treatments show promise in changing the directivity and reducing the magnitude of this tone. Each of the categories of tip modification; anhedral, swept and tapered show potential in reducing the overall sound pressure levels as well as the blade passing frequency tone while providing the same thrust output as the unmodified blade. Numerical simulations using the SU2 solver were performed on selected tip modifications to provide further insights into the effects of changing the propeller tip geometry while in forward flight conditions. The numerical simulation results correlate well with the experimental data.

Interactions of Propellers in Edgewise Flight with Turbulence

“…Experiments to investigate the effects of turbulent inflow on a single propellers aerodynamic and aeroacoustic performance in edgewise flight was undertaken in the University of Bristol pressure-neutral aeroacoustic wind tunnel. This wind tunnel has been used in previous studies to investigate propeller aerodynamics and aeroacoustics [27]. The tunnel is an open section, closed-loop wind tunnel.…”

“…The propeller has a constant pitch of 6" and features a Clark-Y airfoil with a varying chord, 𝐶, across each radial section. The propeller pitch-to-diameter ratio (P/D) of 0.5 was selected as it is within a P/D range consistent with off-the-shelf propellers with a good performance in static hovering flight [27]. A full description of the propellers spanwise pitch and chord distribution is presented in Fig.…”

“…These rotational rates were tested to factor in effects of compressible flow which are likely to occur in real flight conditions (𝑀 𝑇 > 0.3). Crucially, the reader must note that comparisons between FOM are only valid when the disk loading of the propeller, 𝐷 𝐿 = 𝑇/𝐴, is equal between cases [27,37]. As a result comparison of static FOM to determine respective efficiencies across both RPM conditions is not valid.…”

Numerical and experimental investigation of propeller noise with trailing-edge serrations

“…Aerodynamic loads were measured by a 6-component ATI mini40 multi axis load cell fitted directly behind the motor; giving an isolated load path. The test rig used in this study has been previously utilised in previous experiments which can offer further information on the test rig and setup [17][18][19][20][21][22].…”