Linear and nonlinear modeling of self-excited acoustic oscillations in a T-shaped thermoacoustic engine

Geng Chen,Aidong Deng,Haitian Hao

doi:10.1063/5.0059774

Abstract

Branch tubes are often used in thermoacoustic engines (TAEs) for acoustic power extraction or acoustic field adjustment. Their roles, although critical for the performance of the thermoacoustic system, are not fully understood yet. To address this issue, this study investigates the self-excited acoustic oscillations inside a T-shaped TAE where a branch tube is connected to a classical standing-wave TAE. First, system-level theoretical models based on the linear acoustic and thermoacoustic theories in the frequency domain were established to study the acoustic modes and their stability. System-wide computational fluid dynamics (CFD) simulations were carried out to simulate the evolution of the unstable acoustic modes from the initial start-up to the steady state in the time domain. Second, parametric studies on the coupling position of the branch tube and its length were conducted. The effects of the coupling position and branch length on the natural frequencies and mode shapes of the T-shaped TAE were determined by theoretical derivations and substantiated by CFD simulations. The growth/attenuation rate of each acoustic mode was also examined. The CFD results show that bifurcation in steady-state dynamics occurs when the coupling position is altered or the branch length is increased. The steady-state behavior of the T-shaped TAE can transit from limit-cycle oscillations to quasi-periodic oscillations, or vice versa. The theoretical and CFD methodologies in this work are valuable in comprehending the acoustic/dynamic characteristics of the T-shaped standing-wave TAE, providing useful guidelines for studying the coupling of external loads in traveling-wave thermoacoustic systems that usually have more complex structures but are inherently more efficient.

Highlights

This study focuses on the self-excited acoustic oscillations inside a T-shaped Thermoacoustic engines (TAEs) that consists of a classical standing-wave TAE, coupled with a branch tube
The computational fluid dynamics (CFD) results agree well with the linear theory, which gives credence to the theoretical and CFD models used in this study
This paper focused on the self-excited acoustic oscillations, from linear to nonlinear regimes, inside a T-shaped thermoacoustic engine (TAE)

Summary

Introduction

Thermoacoustic engines (TAEs) are thermally-driven devices that produce high-intensity acoustic power from external heat flows by using no/fewer moving components and environmentally friendly working fluids (e.g., air and inert gases). They offer a new approach to recovering the large amount of untapped low-grade heat, such as industrial waste heat, solar energy, and geothermal energy, which is beneficial for addressing the energy shortage and greenhouse gas emission problems faced by the globe. The fundamental working principle of TAEs is the thermoacoustic effect that concerns the thermal-acoustic energy conversion between the still solid and oscillatory fluid within the thermal boundary layers. InTAEs, a piece of porous material dubbed a “stack” or “regenerator,” which has a large effective fluid–solid contact area, is often employed to enhance the thermoacoustic effect.In the literature, TAEs are normally classified into standingwave and traveling-wave types. Thermoacoustic engines (TAEs) are thermally-driven devices that produce high-intensity acoustic power from external heat flows by using no/fewer moving components and environmentally friendly working fluids (e.g., air and inert gases).. Thermoacoustic engines (TAEs) are thermally-driven devices that produce high-intensity acoustic power from external heat flows by using no/fewer moving components and environmentally friendly working fluids (e.g., air and inert gases).1,2 They offer a new approach to recovering the large amount of untapped low-grade heat, such as industrial waste heat, solar energy, and geothermal energy, which is beneficial for addressing the energy shortage and greenhouse gas emission problems faced by the globe.. Classical standing-wave TAEs consist of a straight tube with one end or both ends closed, a stack, and two heat exchangers.. Classical traveling-wave TAEs consist of a scitation.org/journal/adv looped tube, a regenerator, and two heat exchangers.. They often have more complex configurations and may suffer from nonlinear mass streaming.

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