Coexistence and transition of weak and strong wave turbulence in acoustic broadening

This study experimentally demonstrates the coexistence and transition between weak and strong wave turbulence during the interaction of acoustic waves and turbulent flows. We identify conditions under which different wave turbulence regimes occur based on the wavenumber of the turbulent flow and acoustic waves. As the sound frequency increases, strong wave turbulence dominates, requiring a specific scaling factor to reconcile the spectra with the weak turbulence theory. Our analysis using the wave turbulence framework is confirmed by experimental results, providing deep insights into the complex interaction between acoustics and turbulence.

Methods
Our experiments take place in an anechoic wind tunnel with a 0.4 m0.4 m jet nozzle at the Hong Kong University of Science and Technology (39). By introducing turbulence through jet injection into the surrounding medium, we can examine the interaction between incident sound waves and turbulent shear layers. This interaction can trigger both weak and strong wave turbulence, generating additional sound waves that we capture in the opposite direction. To capture the intricate dance of these waves, we use a highly sensitive microphone, GRAS 46BE, at a sampling frequency of 100 kHz for 1 s using a National Instruments-PXIE 4497 system. We conduct 75 independent measurements for each working condition to ensure repeatability. We also use a Dantec hot-wire X-Probe to scan the flow field of the jet from the wind tunnel at a spatial resolution of 1 cm and a temporal sampling frequency of 100 kHz. The acoustic propagating distance is 1.4 m, while the hot-wire X-Probe measurement distance is 0.6 m.