Abstract
A detailed study of the three-dimensional sound fields around a monopole point source in subsonic and supersonic rotation is investigated. We calculate the sound pressure, the acoustic velocity, as well as the instantaneous and time-averaged acoustic intensity fields with the advanced time approach. The advanced time approach is applied for sound sources at subsonic and supersonic rotation and yield comparable results as those obtained from the spherical harmonic series expansion method or the solution of the retarded time equation. Further, the direction of the time-averaged acoustic energy flow is derived from the acoustic intensity vectors. It is shown, that the direction of the energy flow path differs from the radial direction and depends on the rotational direction and rotational velocity. Those findings are useful, for example, to improve the acoustic absorption performance of sound absorbers and acoustic liners around turbomachines.
Highlights
Turbomachines, like axial fans or aircraft engines, are often used in direct vicinity of humans due to their applications in transportation, cooling and air-conditioning
The calculation of the sound field and the acoustic energy flow may help to develop and to improve the acoustic absorption performance of micro-perforated duct absorber of axial fans [1,2,3] and acoustic liners, which were integrated into the casing around an aircraft engine [4, 5]
The waveform of the pressure signal is reproduced well compared to the other methods, but high sampling rates are needed and a low-pass filter has to be applied to the time signals
Summary
Turbomachines, like axial fans or aircraft engines, are often used in direct vicinity of humans due to their applications in transportation, cooling and air-conditioning. The calculation of the sound field and the acoustic energy flow may help to develop and to improve the acoustic absorption performance of micro-perforated duct absorber of axial fans [1,2,3] and acoustic liners, which were integrated into the casing around an aircraft engine [4, 5] For those absorbers, the best absorption performance is obtained if the angle of the acoustic intensity vector corresponds to the normal direction of the absorbing surface.
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