Aeroacoustic Wind Tunnel experiments on propeller noise at the University of Bristol

This presentation will describe the various types of experimental propeller test campaigns conducted in the national Aeroacoustic wind tunnel (Aeroacoustic facility | Fluid and Aerodynamics Research Group | University of Bristol) and the national Pressure neutral acoustic wind tunnel (Pressure-neutral acoustic wind tunnel | Fluid and Aerodynamics Research Group | University of Bristol) at the University of Bristol in collaboration with academic and industrial partners. The experimental campaigns incorporated a wide range of techniques including far-field microphone arrays, near-field pressure measurements, Particle-Image-Velocimetry, and hot-wire flow-field measurements to create large datasets, and to permit a comprehensive evaluation of the key flow behaviour and noise characteristics produced by propellers. Observations on acoustic directivity, and spectral content were also related to noise generation mechanisms, and their sensitivity to operational and design parameters. The propeller test configurations investigated include:
1.Distributed electric propulsion [1,2] – Where multiple propellers are distributed in parallel along the wing of an electric vertical take-off and landing (eVTOL) aircraft.
2.Boundary layer ingestion [3] – A configuration where the propellers are located close to the aircraft body such that it ingests the boundary layer and is a propulsion-airframe installation configuration.
3.Tilting rotors [4] – Used on vertical take-off and landing (VTOL) aircraft where the propellers can tilt vertically for vertical lift and horizontally for forward flight.
4.Edge-wise flight [5-7] – A configuration where the propeller axis is vertical and is subject to horizontal winds. This simulates the take-off and landing conditions of eVTOLs under windy conditions.
5.Scale model eVTOL aircraft – The University of Bristol is currently collaborating with an eVTOL company based in Bristol to build and test a 10 % scale model of its aircraft to assess the noise generated by their propellers in the national wind tunnel facilities.
The experimental setups and studies performed at the University of Bristol in the field of propellers laid the groundwork for the current project of designing and building the versatile National Propeller Testbed (NPTB).

References:
[1]Luke Bowen, Burak Turhan, Hasan Kamliya Jawahar, Djamel Rezgui and Mahdi Azarpeyvand. "Aeroacoustic characteristics of distributed electric propulsion configuration with turbulent flows," AIAA 2023-4294. AIAA AVIATION 2023 Forum. June 2023.
[2]Burak Turhan, Hasan Kamliya Jawahar, Luke Bowen, Djamel Rezgui and Mahdi Azarpeyvand. "Aeroacoustic characteristics of distributed electric propulsion system in forward flight," AIAA 2023-4490. AIAA AVIATION 2023 Forum. June 2023.
[3]Ismaeel Zaman, Michele Falsi, Bin Zang, Mahdi Azarpeyvand, Roberto Camussi. "Aeroacoustics of the propeller Boundary Layer Ingestion configuration for varying thrusts,” Journal of Sound and Vibration. 589 118604. 2024.
[4]Nur Syafiqah Jamaluddin, Alper Celik, Kabilan Baskaran, Djamel Rezgui, Mahdi Azarpeyvand. "Aerodynamic noise analysis of tilting rotor in edgewise flow conditions,” Journal of Sound and Vibration. 582 118423. 2024.
[5]Liam P. Hanson, Luke Bowen, Bin Zang and Mahdi Azarpeyvand. "Interactions of Propellers in Edgewise Flight with Turbulence," AIAA 2023-3656. AIAA AVIATION 2023 Forum. June 2023.
[6]Jamaluddin, Nur Syafiqah, Alper Celik, Kabilan Baskaran, Djamel Rezgui, and Mahdi Azarpeyvand. "Experimental Analysis of Rotor Blade Noise in Edgewise Turbulence" Aerospace 10, no. 6: 502. 2023.
[7]Liam P. Hanson, Bin Zang and Mahdi Azarpeyvand. "Experimental Characterisation of Cylinder-Induced Turbulence Ingestion in Propellers Operating in Edgewise Flight," AIAA 2024-3100. 30th AIAA/CEAS Aeroacoustics Conference (2024). June 2024.