Measurements of inner and outer streaming vortices in a standing waveguide using laser doppler velocimetry

Abstract

Measurements of the axial streaming velocity are performed by means of laser doppler velocimetry in an experimental apparatus consisting of a waveguide having loudspeakers at each end for high intensity sound levels. Streaming is characterized by an appropriate Reynolds number Re(NL), the case Re(NL)<<1 corresponding to the so-called slow streaming and the case Re(NL)>/=1 being referred to as fast streaming. The variation of axial streaming velocity with respect to the transverse coordinate is compared to the available slow streaming theory. Streaming fluid flow is measured both in the core region and in the near wall region. Streaming velocity in the center of the guide agrees reasonably well with the slow streaming theory for small Re(NL) but deviates significantly from such predictions for Re(NL)>20 and its evolution for further increasing Re(NL) is discussed. Then streaming behavior in the near wall region is particularly studied. For Re(NL)<70, two vortices are present across the guide section as predicted by slow streaming theory. Then it appears that, when the Reynolds number is increased, two other vortices become visible in the near wall region. Different stages for the generation and evolution of these inner streaming vortices are presented.

Fast acoustic streaming in standing waves: Generation of an additional outer streaming cell

“…The LDV measurements yield the Eulerian particle velocity. In agreement with Moreau et al 11 , measurements were performed more than 26 min after the acoustic field is switched on and are stable after this time. Also, following this latter reference, in order to reach convergence in the measured streaming velocity, we choose to acquire either 70000 points or to stop acquisition after 10…”

Two-dimensional numerical simulations of nonlinear acoustic streaming in standing waves

“…This motion 5 was initially studied by Rayleigh [1] in the case of wide channels, in which the 6 boundary layer thickness is negligible in comparison with the channel width. streaming recently observed in several experimental works [7,8,9], where 33 the temperature gradient along the resonator wall has a significant influence. …”

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.…”