Measurement of acoustic streaming in a closed-loop traveling wave resonator using laser Doppler velocimetry

Abstract

This paper deals with the measurement of acoustic particle velocity and acoustic streaming velocity in a closed-loop waveguide in which a resonant traveling acoustic wave is sustained by two loudspeakers appropriately controlled in phase and amplitude. An analytical model of the acoustic field and a theoretical estimate of the acoustic streaming are presented. The measurement of acoustic and acoustic streaming velocities is performed using laser Doppler velocimetry. The experimental results obtained show that the curvature of the resonator impacts the acoustic velocity and the profile of acoustic streaming. The quadratic dependence of the acoustic streaming velocity on the acoustic pressure amplitude is verified and the measured cross-sectional average streaming velocity is in good agreement with the value predicted by the theoretical estimate.

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.…”

Weakly Nonlinear Propagation in Thermoacoustic Engines: A Numerical Study of Higher Harmonics Generation up to the Appearance of Shock Waves

“…The saturation of the growth of amplitude is then controlled by nonlinear phenomena which are the cause for both acoustic and thermal power dissipation. Among the many effects usually described are the acoustically enhanced thermal pumping [1,2], acoustically induced DC flows [3,4,5], complex aerodynamical effects due to geometrical singularities at interfaces between elements of different porosity or at geometric discontinuities [6], or nonlinear propagation leading to higher harmonics generation [7,8].…”

Active control of thermoacoustic amplification in an annular engine

“…Note that the placement of the acoustic sources, separated by a distance L 2 − L 1 Ϸ L / 4, has not been chosen aimlessly: it has been demonstrated 23,24 that in the case of a closed-loop resonator of unwrapped length L, it is possible, by means of two acoustic sources separated by a distance L / 4 and operating at frequency f 0 = c 0 / L ͑where c 0 stands for the sound velocity͒, to sustain an acoustic field which have the characteristics of a traveling wave ͑if the drivers are / 2 out of phase͒, a standing wave ͑if the drivers are in phase͒, or any intermediate situation ͑in terms of standing/traveling wave component͒. Each of these sources is an electrodynamic loudspeaker ͑model Audax HP 170 MO͒ loaded by a rear enclosure of volume V Ӎ 6.4ϫ 10 −3 m 3 , and connected to the waveguide through a cylindrical tube of circular cross section ͑radius r 0 = 3 mm, length l 0 =30 mm͒.…”

“…23 An experimental study is undertaken to investigate the possibility to tune the acoustic field inside the thermoacoustic core, by two loudspeakers, so that the thermoacoustic amplification process is maximized and the overall efficiency of the thermoacoustic engine ͑accounting for the electrical energy provided to the loudspeakers͒ is larger than its initial value without active control. This control ͑here called "active" to denote that, unlike passive methods, it requires to supply additional energy into the system in order to control its performances͒ is applied to an annular thermoacoustic engine, for which the presence of a closed-loop waveguide allows an easy control of the acoustic field by means of two acoustic transducers appropriately tuned in terms of amplitude, frequency and relative phasing.…”