Shocked and unshocked thermoacoustic oscillations in a looped tube

Sugimoto, Naotoshi; Minamigawa, Keisuke

doi:10.1121/2.0000847

Cited by 3 publications

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“…For the difference between the shocked and unshocked oscillations in the case of 100 cells=in 2 , see Sugimoto and Minamigawa. 18) Next the axial distributions of pressure amplitudes measured are discussed in light of the linear theory for the 1-wave mode at the marginal state. For the case of the stacks of 600 cells=in 2 with R s ¼ 0:48 mm and ¼ 0:86, Fig.…”

Section: Pressure Profiles Of the Oscillationsmentioning

confidence: 99%

Experiments on Self-excited Thermoacoustic Oscillations in an Air-filled Looped Tube with a Pair of Stacks

Sugimoto

Minamigawa

2018

J. Phys. Soc. Jpn.

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This paper investigates experimentally the onset of thermoacoustic instability and ensuing emergence of self-excited oscillations of air in a looped tube with a pair of identical stacks installed inside on diametrically opposite positions. Each stack is sandwiched by hot and cold (ambient) heat exchangers so that a temperature gradient may be imposed on it in the same sense. The loop is circular except for two short straight sections in which the stack and the heat exchangers are housed. Four sets of stacks of 100, 300, 600, and 900 cells=in 2 are used to examine influences of stack's pore radius on the onset of instability and the steady state of oscillations. It is found that thermoacoustic self-excited oscillations emerge spontaneously for all sets of the stacks in a 1-wave mode where the loop length corresponds to one wavelength of oscillations. It is also found that for the stacks of 900 cells=in 2 , a 2-wave mode also emerges besides the 1-wave mode. Temperatures of the heaters are constantly monitored and excess pressures are measured at four positions. The onset of instability is examined in light of marginal conditions obtained theoretically and step-up behaviors are discussed in terms of the temperature ratio and the growth rate. It is revealed that the pressure profiles of oscillations at the steady state propagate along the loop in the same sense as the temperature gradient and that the peak-to-peak pressure takes a maximum near the stack. As it increases, emergence of acoustic shock waves is observed except for the case with the stacks of 100 cells=in 2. Physical mechanisms of shock formation are discussed in terms of eigenfrequencies of oscillations in higher modes.

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Section: Pressure Profiles Of the Oscillationsmentioning

confidence: 99%

Experiments on Self-excited Thermoacoustic Oscillations in an Air-filled Looped Tube with a Pair of Stacks

Sugimoto

Minamigawa

2018

J. Phys. Soc. Jpn.

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Marginal conditions for the onset of thermoacoustic oscillations due to instability of heat flow

Sugimoto

2018

IMA Journal of Applied Mathematics

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This paper derives marginal conditions for the onset of thermoacoustic oscillations of a gas due to instability of heat flow in a closed tube and a looped tube. Steady heat flow is created by installing in the tube a stack consisting of many pores axially, sandwiched by hot and cold heat exchangers to impose a temperature gradient. Assuming a time-harmonic disturbance and a temperature gradient given, an eigenvalue problem is posed on Rott's equation. Given a pore radius of the stack, a marginal condition is determined so that an unknown frequency may take a real value by a suitable choice of a temperature ratio and neutral oscillations may occur. This problem is solved numerically by a shooting method combined with Runge-Kutta method and Newton's method. The marginal conditions for the temperature ratio are displayed in curves versus the pore radius relative to a typical thickness of viscous diffusion layer. At marginal states corresponding to the conditions obtained, angular frequencies of neutral oscillations are also displayed. The same problem is solved by using the approximate equations derived from the thermoacoustic-wave equation for a case of thin or thick diffusion layer relative to a pore radius. Comparing the marginal conditions and the angular frequencies against the ones by Rott's equation, the validity of the approximate equations is checked. Influences of the porosity on the marginal conditions and the angular frequencies are examined. Also obtained are those in higher modes of oscillations in both tubes. Finally axial variations of amplitudes in pressure and mass flux density and of acoustic energy flux density (intensity) at a marginal state in the lowest mode are displayed to highlight physical differences between a standing wave in the closed tube and a travelling wave in the looped tube.

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A unified approach for dynamic characteristic analysis of a standing-wave thermoacoustic engine with general impedance ends

Guo

Liu

2022

Journal of Vibration and Control

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As promising devices for energy conversion, thermoacoustic engines (TAEs) are attracting more and more research attention with regard to renewable thermal energy application. For a TAE, the oscillation frequency is a critical parameter in its design and operation, which can only be estimated currently through an often tedious process using a shooting method or a numerical iteration method, and an analysis model with classical boundary conditions. In this context, this study seeks to establish a unified model for dynamic analysis of a one-dimensional (1D) standing-wave TAE with general impedance ends. First, the differential equations governing the thermoacoustic behavior of the TAE and its impedance boundary conditions are simultaneously solved using the Galerkin method and an improved Fourier series expansion method. Then, the characteristic distributions of oscillation frequency, sound pressure, and volume flow rate are obtained by solving a standard eigenvalue problem. Finally, the effects of engine length, stack length and position, and impedance ends on the dynamic behavior of the TAE’s thermoacoustic system are investigated and analyzed. The results show that engine length has a significantly negative correlation with the modal frequencies in different working gases, and stack position and stack length have a slight effect on the oscillation frequency of the TAE. The arbitrary variations in impedance boundary conditions can be simulated from the open end to the rigid wall and all intermediate cases. The proposed model can efficiently predict changes in dynamic parameters of 1-D TAEs with impedance ends in a unified pattern and can serve as a reliable analysis tool for further research on TAEs coupled with various energy harvesters.

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Shocked and unshocked thermoacoustic oscillations in a looped tube

Cited by 3 publications

References 0 publications

Experiments on Self-excited Thermoacoustic Oscillations in an Air-filled Looped Tube with a Pair of Stacks

Experiments on Self-excited Thermoacoustic Oscillations in an Air-filled Looped Tube with a Pair of Stacks

Marginal conditions for the onset of thermoacoustic oscillations due to instability of heat flow

A unified approach for dynamic characteristic analysis of a standing-wave thermoacoustic engine with general impedance ends

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