Abstract
The self-excited thermoacoustic instability in a two-dimensional Rijke-type burner with a center-stabilized premixed methane–air flame is numerically studied. The simulation considers the reacting flow, flame dynamics, and radiation model to investigate the important physical processes. A finite volume-based approach is used to simulate reacting flows under both laminar and turbulent flow conditions. Chemical reaction modeling is conducted via the finite-rate/eddy dissipation model with one-step reaction mechanisms, and the radiation heat flux and turbulent flow characteristics are determined by using the P-1 model and the standard k-ε model, respectively. The steady-state reacting flow is first simulated for model verification. Then, the dynamic pressure, velocity, and reaction heat evolutions are determined to show the onset and growth rate of self-excited instability in the burner. Using the fast Fourier transform (FFT) method, the frequency of the limit cycle oscillation is obtained, which agrees well with the theoretical prediction. The dynamic pressure and velocity along the tube axis provide the acoustic oscillation mode and amplitude, also agreeing well with the prediction. Finally, the unsteady flow field at different times in a limit cycle shows that flame-induced vortices occur inside the combustor, and the temperature distribution indicates that the back-and-forth velocity changes in the tube vary the distance between the flame and honeycomb in turn, forming a forward feedback loop in the tube. The results reveal the route of flame-induced thermoacoustic instability in the Rijke-type burner and indicate periodical vortex formation and breakdown in the Rijke burner, which should be considered turbulent flow under thermoacoustic instability.
Highlights
In 1859, Rijke discovered strong acoustic oscillations when heat was added to the lower half of a vertical tube opened at both ends [1]
One type in which the flow is combustible gas and the heat is produced by the flame is called a Rijke burner or a Rijke tube burner
Chatterjee investigated the occurrence of combustion instabilities in a Rijke tube-type combustor using a two-dimensional (2-D) finite volume method, captured the instability growth to a limit cycle of the pressure oscillation, and predicted the frequency and magnitude of the thermoacoustic instability [21]
Summary
In 1859, Rijke discovered strong acoustic oscillations when heat was added to the lower half of a vertical tube opened at both ends [1]. Chatterjee investigated the occurrence of combustion instabilities in a Rijke tube-type combustor using a two-dimensional (2-D) finite volume method, captured the instability growth to a limit cycle of the pressure oscillation, and predicted the frequency and magnitude of the thermoacoustic instability [21]. On the research of the interaction of turbulence and combustion, numerical simulation has shown its extraordinary ability [26] These CFD simulations help in understanding the detailed flow parameters, such as pollution control, efficiency enhancement, and mass transport processes, for further analysis and can serve as an aid to engineers and designers for building combustion systems with a decreased possibility of thermoacoustic instabilities. The results of this work show that there are vortices in the Rijke-type burner when thermoacoustic instability occurs, and it should be considered a turbulent reacting flow field
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