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Etude expérimentale et théorique des processus non linéaires de saturation dans un générateur d'ondes thermoacoustique annulaire

Abstract : For the transformation of thermal energy into mechanical energy, thermoacoustic prime movers employ the interaction between an inhomogeneously heated stack of solid plates and gas oscillations, which results in the onset of self-excited acoustic oscillations. For the past ten years, an important research effort has been devoted to the study of nonlinear processes which are responsible for the saturation of the acoustic wave amplitude; experimental observations were not only poorly mastered and badly documented, but were also unexplained because of the lack of adequate models to describe such complex processes. Thus, the work presented in this report has been initiated to list, classify, interpret the experimental observations analytically, and to propose a model able to describe various transient regimes in an annular thermoacoustic prime mover.

The experimental results obtained for various heating processes show complicated transient regimes : periodic switch on-off of the acoustic wave, low frequency modulation of the acoustic wave amplitude, double-threshold effect during the onset of the thermoacoustic instability and so on. Significant variations of the temperature field have also been observed during these transient regimes indicating that, in addition to the classical cascade process of higher harmonic generation and minor losses (vortex generation at the edges of the stack), the nonlinear processes involving interaction between acoustic and temperature fields play an important role in the dynamics of the transient regime. In particular, the development of a high amplitude acoustic field induces both thermoacoustic enthalpy flow (equivalent to acoustically enhanced thermal conductivity of the stack walls) and acoustic streaming which modifies the shape of the temperature field.

The influence of sound amplification on temperature distribution is studied analytically, and shows that the distribution of the acoustic field (pressure, velocity and phase shift), and consequently the thermoacoustic amplification, strongly depends on the shape of the temperature field. Then, the analytical description of the above mentioned nonlinear effects and of the transient interaction between acoustic and temperature fields is proposed : the simulation results are very close to experimental results, thus confirming the major role of acoustically enhanced conductivity and acoustic streaming. Finally, a more qualitative description of the transient regime is proposed as a set of ordinary differential, equations, and allows to extract the predominant physical processes.

Because it supplies a new undestanding of fundamental processes which control the acoustic wave saturation, this work contributes, in our opinion, to the progress in designing thermoacoustic engines so that they become much more efficient.
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https://tel.archives-ouvertes.fr/tel-00008096
Contributor : Guillaume Penelet <>
Submitted on : Monday, January 17, 2005 - 2:09:36 PM
Last modification on : Tuesday, March 31, 2020 - 3:21:02 PM
Long-term archiving on: : Friday, April 2, 2010 - 9:41:50 PM

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  • HAL Id : tel-00008096, version 1

Citation

Guillaume Penelet. Etude expérimentale et théorique des processus non linéaires de saturation dans un générateur d'ondes thermoacoustique annulaire. Acoustique [physics.class-ph]. Université du Maine, 2004. Français. ⟨tel-00008096⟩

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