When acoustic waves propagate through turbulent pipe flow, the coherent incident signal can be scattered and distorted due to the random change of the physical properties in the turbulence. This paper experimentally investigates the propagation of high frequency acoustic waves in a low Mach number turbulent pipe flow. A linear modulated wave signal from 5kHz to 70kHz and a Gaussian modulated sine pulse with various central frequencies are used to excite radial-mode waves. We tested each specific frequency signal under different Reynolds number which ranges fromfíe = 2x 104 tofíe = 4x 104. These experimental results demonstrate that the realizations exhibit random fluctuations in both amplitude and phase. When Re > 3 x 104, the amplitude of probing wave exhibits a sharp decay to 10% at 2m away from the source. The mechanism of acoustic waves in high frequency regime attenuated by turbulence is multiple scattering. Under high Reynolds numbers, acoustic waves near the cut-off frequency and higher-order radial-mode waves decrease significantly along the propagation distance due to the multiple zigzag-type paths effects.
Meng et al. (Wed,) studied this question.