Acoustically induced turbulence and shock waves under a traveling-wave condition

Experimental investigations of acoustically induced turbulence and shock waves in a traveling-wave tube are performed with and without the introduction of an air flow through the system. Frequency (f) and intensity (I) effects of the acoustic field are studied using a hot-film anemometer and FFT data processing unit. The effect of the acoustically induced turbulence on a laminar flow is also investigated. Sampled data are first conditioned, then processed to estimate the characteristics of turbulence. It is found that for sound pressure level > 158 dB turbulence appears. Furthermore, at slightly higher level (~160 dB) shock waves appear over the range of all frequency. Turbulence measurements were performed over a frequency range of 500–2200 Hz, with intensity over a range of 06.-4.0 W/cm2. Below I = 0.6 W/cm2 no turbulent bursts are found. The turbulent spectrum F and the wavenumber k are found to safisfy a power law Fαka with a~ — 1.7 to — 2.1. The rms turbulent velocity w. is found experimentally to have a I1/2dependence, yet is relatively insensitive to variation of f. Throughout the whole measuring range of f. and I, the rate of energy dissipation per unit mass ε is estimated to be 106—107cm2/s3. It is also found that superimposing a laminar air stream through the tube will suppress the turbulence.