Experimental investigation of acoustic streaming in a cylindrical wave guide up to high streaming Reynolds numbers

Abstract

Measurements of streaming velocity are performed by means of Laser Doppler Velocimetry and Particle Image Velociimetry in an experimental apparatus consisting of a cylindrical waveguide having one loudspeaker at each end for high intensity sound levels. The case of high nonlinear Reynolds number ReNL is particularly investigated. The variation of axial streaming velocity with respect to the axial and to the transverse coordinates are compared to available Rayleigh streaming theory. As expected, the measured streaming velocity agrees well with the Rayleigh streaming theory for small ReNL but deviates significantly from such predictions for high ReNL. When the nonlinear Reynolds number is increased, the outer centerline axial streaming velocity gets distorted towards the acoustic velocity nodes until counter-rotating additional vortices are generated near the acoustic velocity antinodes. This kind of behavior is followed by outer streaming cells only and measurements in the near wall region show that inner streaming vortices are less affected by this substantial evolution of fast streaming pattern. Measurements of the transient evolution of streaming velocity provide an additional insight into the evolution of fast streaming.

Inertial effects on acoustic Rayleigh streaming flow: Transient and established regimes

“…Fig. 1(b) shows the distorted streaming pattern (result from the numerical simulation N 2 further described in this paper) in the fast streaming regime, when two new streaming cells are observed in the center of the guide, near the acoustic velocity antinode (z/L = 0) [19,28,29]. Several sources could potentially be responsible for this mutation of streaming pattern: thermal effects were considered [26], as well as nonlinear propagation [29] and it was concluded that inertial effects on acoustic streaming could be the main source [29].…”

“…The established streaming flow behavior for high acoustic amplitudes (i.e. in the nonlinear regime of streaming) was previously analyzed numerically [19] (with a DNS code) and experimentally [28]: additional streaming cells were observed inside the resonator [29]. Fig.…”

“…Those measurements are performed at different locations within the streaming cells. The laser system used and the processing of the laser signal are described in [28].…”

“…In the experiments, the establishment of acoustics at low amplitudes is very long (see Fig. 13 of [28]). In this case, the evolution of streaming is intrinsically linked to that of acoustics and the associated establishment time scales, determined by fitting an exp(−t/τ ) law to experimental data, are very close (τ ac = 190 s and τ st = 233 s).…”

Measurement of density fluctuations using digital holographic interferometry in a standing wave thermoacoustic oscillator

“…Laser Doppler Velocimetry and Particle Image Velocimetry provide information about the gas parcel velocity and have been used previously to characterize acoustic streaming [14][15][16][17] or vortex shedding processes [18][19][20], while cold wire anemometry [21] has been used to characterize the nonlinear temperature fluctuations in the vicinity of the stack termination. In this paper, attention is focused on the development of another measurement method allowing to get information about density http://dx.doi.org/10.1016/j.expthermflusci.2015.09.012 0894-1777/Ó 2015 Elsevier Inc. All rights reserved.…”