Div. of Fluid Mech., Dept. of Eng. Mech., Tsinghua Univ., Beijing 100084, People's Republic of China
Shanghai Jiaotong Univ., Shanghai 200030, People's Republic of China
To do research on the aeroacoustic mechanism of turbomachinery or any other rotating machines, it is important to study the acoustic characteristics of the rotating sources. Based on the frequency domain solution of moving sound sources, an approximate acoustic solution of a rotating point source in the near field, which is the superposition of a far-field solution and three near-field modification items, is given if the rotating radius is acoustical compact when compared with the field sound wavelength. Accordingly, the near-field Green's function in free space is obtained. Then, the directionality characteristics of the sound field induced by rotation is discussed, and the influence of source position, source frequency, and rotating frequency is studied in detail. The results reveal that the distribution of near-field modifications is discrete around the viewing angle, and the influence on near-field modification by the rotating radius happens mostly around the rotating plane, while the influence of the axial position of the source happens mostly near the rotating axis.