Abstract
This paper presents a computational study of flow incidence effects on the aeroacoustics of a propeller operating at low blade-tip Mach numbers. The numerical flow solution is obtained by using the Lattice-Boltzmann/Very Large Eddy Simulation method, while far-field noise is computed through the Ffowcs-Williams & Hawkings' acoustic analogy applied on the propeller surface. The presence of an angular inflow leads to: (i) the radiation of tonal loading noise along the propeller axis; (ii) the increment/reduction of the sound pressure level in the region from/to which the propeller is tilted away/towards. However, contrarily to propellers operating at high blade-tip Mach numbers, the noise directivity change is found to be governed only by the rise of periodic unsteady loadings, with the modulation of the strength of the noise sources on the blade, associated to the periodic variation of the observer-source relative Mach number (in the blade reference frame), being negligible. Finally, thickness noise and turbulent boundary-layer trailing-edge noise did not show a significant directivity variation due to the propeller yaw angle change.
Highlights
The use of small-to-medium size fully-electric flying vehicles in large metropolitan areas, from drones and Unmanned Aerial Vehicles (UAVs) for goods delivery to Personal Aerial Vehicles (PAVs) for people mobility, is envisaged in the near future as a solution to roads congestion [1,2]
The employed computational approach, which is based on the use of a zig-zag transition trip to promote the generation of resolved pressure fluctuations within the boundarylayer that are scattered as sound at the blade trailing-edge, is able to capture the moderate changes of the broadband noise levels at high frequency due to the change of the propeller yaw angle
This paper presented a computational study on flow incidence effects on the aeroacoustics associated to low-speed propeller operated at a yaw angle with respect to the free-stream
Summary
The use of small-to-medium size fully-electric flying vehicles in large metropolitan areas, from drones and Unmanned Aerial Vehicles (UAVs) for goods delivery to Personal Aerial Vehicles (PAVs) for people mobility, is envisaged in the near future as a solution to roads congestion [1,2]. A method for rotating steady line sources (acoustically compact), accurate to the first order in the in-plane Mach number, was formulated by Mani [16] He included, in a frequency domain farfield method, the effect of the propeller yaw angle on the radiation of both the steady loading and thickness noise, in addition to that of the unsteady loading. Envia [19] proposed a frequency domain formulation based on a moving-medium variant of the Ffowcs-Williams & Hawkings’ equation to predict the noise from a propfan operating at incidence His approach involved the use of the Airy’s function and its derivatives, as alternative to numerical integration, and incorporated both in-plane convective effects and loading unsteadiness with no limitations on the source chordwise compactness, showing a rather favorable agreement with the experimental data.
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