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- Title
Rotor aeroacoustic response to an axisymmetric turbulent boundary layer.
- Authors
Di Zhou; Kan Wang; Meng Wang
- Abstract
The acoustic response of a five-bladed rotor to an axisymmetric turbulent boundary layer at the tail end of a body of revolution (BOR) is investigated numerically to elucidate the physical sources of acoustics, particularly the role of coherent structures in sound generation. The BOR is at a length-based Reynolds number of 1.9 × 106 and free-stream Mach number of 0.059. Two rotor advance ratios, 1.44 and 1.13, are considered. The turbulent boundary layer on the nose and midsection of the BOR is computed using wall-modelled large-eddy simulation, whereas that in the acoustically important tail-cone section is wall-resolved. The radiated acoustic field is calculated using the Ffowcs Williams-Hawkings equation. The computed flow statistics and sound pressure spectra agree well with the experimental measurements at Virginia Tech. In addition to broadband turbulence-ingestion noise, spectral humps near multiples of the blade-passing frequency and accompanying valleys are captured. They are shown to be caused by correlated blade unsteady-loading dipole sources and their constructive and destructive interference as a result of successive blades cutting through the same coherent structures. The latter undergo rapid growth in the decelerating tail-cone boundary layer before their interaction with the rotor. The acoustic radiation is dominated by the outer region of the blade owing to a combination of larger blade chord-length, inflow turbulence intensity and blade speed. The numerical results also correctly predict the effect of the rotor advance ratio on the acoustic field. A mixed free-stream/convection Mach-number scaling successfully collapses the sound pressure spectra at the two advance ratios.
- Subjects
VIRGINIA Polytechnic Institute &; State University; TURBULENT boundary layer; MACH number; SOUND pressure; REYNOLDS number; PHYSICAL acoustics; BOUNDARY layer (Aerodynamics); ACOUSTIC vibrations; ROTOR vibration
- Publication
Journal of Fluid Mechanics, 2024, Vol 981, p1
- ISSN
0022-1120
- Publication type
Article
- DOI
10.1017/jfm.2024.29