Article ID: e24.121
Amplitude modulations of an aerodynamic sound by sound source movement or convection is investigated experimentally. The directivities of an aeolian tone sound radiated from a cylinder fixed in a wind tunnel were measured with horizontally aligned microphones outside the flow as a simplified dipole component of aerodynamic sound generated by pressure fluctuations, which is dominant at low Mach number. The results show that the acoustic intensity of radiated sound can increase approximately in inverse proportion to the fourth power of the ratio of the apparent wavelength of the radiate sound to the original wavelength. The amplitude modulation of the sound by convection was measured and then compared with the modulation of the same sound by source movement. The result revealed that an aerodynamic sound leads to a larger amplitude modulation by source movement compared with the modulation measured in a wind tunnel experiment, although the apparent wavelength of sound radiated from the same source in the atmosphere changes by the same proportion.
