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

Abstract

a b s t r a c tThis paper describes an optical set-up for measuring density fluctuations associated to acoustic oscillations in a thermoacoustic prime-mover. A time-resolved, full-field holographic interferometry technique is used, which enables to measure the optical phase difference between a reference beam and a probe beam passing through the acoustic resonator. The paper first presents the experimental set-up and the processing of holograms from which the instantaneous variations of the gas density along the line of sight of the probe beam are obtained. Then, the measurement technique is applied to the analysis of density fluctuations in the neighborhood of the heated side of a stack in a standing wave thermoacoustic prime mover during the transient regime of wave amplitude growth. The experimental results reveal that there exists very significant entrance effects, which lead to the generation of higher harmonics as well as mean (time-averaged) mass rarefaction in the vicinity of the stack termination. Finally, a short discussion is provided, based on a simplified modeling of higher harmonics generation in temperature associated to the oscillations of an inviscid gas through the stack, but the model fails in explaining the magnitude of the phenomena observed.

Cold wire constant voltage anemometry to measure temperature fluctuations and its application in a thermoacoustic system

“…A model for temperature fluctuations developed by Gusev et al 20 predicts a nonlinear character of the temperature oscillations close to the stack. Berson et al 21 and Penelet et al 1 experimentally confirmed the appearance of harmonics. Even though no harmonic decomposition has been made in the present study, Figure 15 strongly supports the hypothesis of nonlinearities in the temperature signal clearly visible for point A.…”

“…where χ is the temperature coefficient of resistivity and R 0 the resistance of the wire at the reference temperature T 0 . For an ideal cold wire devoid of thermal inertia and placed in a flow of instantaneous temperature T a (t), relation (1) gives…”

“…Recently, Penelet et al 1 presented the measurement of a temperature field in a thermoacoustic oscillator using digital holographic interferometry. As this method is an optical method, it necessitates optical access to the test area.…”

Common features in the thermoacoustics of flames and engines

“…In practice, this suppression is achieved more or less empirically by means of jetpumps' 17 membranes 19 or tapered tubes. 92 However, Penelet et al 93 have shown that the amplification may actually be increased by the streaming through its influence on the shaping of the temperature field.…”

Determination of Dynamic Viscosity of Viscous Oils using Mach Zehnder Digital Holographic Method

“…For example, the plankton and other marine organisms as well as bacteria and fruit flies have been explored using the DH method (Sun et al, 2007;Xu et al, 2001). The density fluctuations of a standing wave in a thermoacoustic oscillation (Penelet et al, 2015) and the phase compensation of spherical beam (Sánchez-Ortiga et al, 2011) have been analyzed by the hologram patterns as well. The fingerprint patterns of human can also be observed and separated by investigating their profile intensity fringes (Plaipichit and Buranasiri, 2014).…”