Theoretical and experimental demonstration of minimizing self-excited thermoacoustic oscillations by applying anti-sound technique

The Journal of the Acoustical Society of America

2018

In this work, the effects of background noises on nonlinear dynamics of a modelled standing-wave thermoacoustic system with subcritical Hopf bifurcation behaviors are studied. These noises include (1) pressure-coupled (acoustic), (2) velocity-coupled (flow), and (3) external combustion noise. It is found that these three types of background noises play important, but different roles in changing the hysteresis width and stability boundary. In addition, the stochastic transition from stability to instability is investigated, as the noise intensity is varied. Two different stochastic P-bifurcations are identified. One is related to a craterlike probability density distribution. The other is associated with a probability density distribution characterized with two peaks and one trough. With each type of noise affecting the system's stochastic behaviors being evaluated, the effect of two different types of noises is then studied. It is shown that the combined noises (types 1 and 2) cannot only destabilize global stable thermoacoustic system, but also stabilize linearly unstable system. This depends strongly on the superimposition form of the two types of noises. In addition, when the thermoacoustic system is disturbed by the combined noise (types 3 and 1 or types 3 and 2), the transition process is dominated by the combustion noise.

Section: The Nonlinear Thermoacoustic Modelmentioning

confidence: 99%

Effects of background noises on nonlinear dynamics of a modelled thermoacoustic combustor

The Journal of the Acoustical Society of America

2018

“…Equivalence ratio Ф is a critical parameter indicating combustion conditions such as rich or lean combustion. Ф denotes the fuel air ratio, which affect the combustion efficiency and thermoacoustic stability [40,41]. When stoichiometric combustion (also known as complete combustion) occurs, ϕ = 1.0.…”

Section: Description Of Experimentsmentioning

confidence: 99%

Experimental study of equivalence ratio and fuel flow rate effects on nonlinear thermoacoustic instability in a swirl combustor

et al. 2017

Applied Energy

Self Cite

Industrial combustion systems such as power generation gas turbines, rocket motors, furnaces and boilers often face the problem of large-amplitude self-excited pressure oscillations that occur due to the onset of thermoacoustic instability. To prevent the onset of such instability, understanding the effects of fuel-air equivalence ratio ϕ, fuel flow rate V f on self-excited nonlinear thermoacoustic oscillations is of fundamental and practical importance. Experimental investigation of the roles of these parameters on triggering thermoacoustic instability in a swirl combustor has received very little attention. In this work, we design a swirling thermocoustic combustor and conduct a series of experimental tests. Autocorrelation and recurrence analysis of phase space trajectories reconstructed from the acoustic pressure time trace are performed. These experimental tests allow us to study the effect of fuel-air equivalence ratio ϕ on the onset of thermoacoustic instability by varying the fuel volume flow rate V f . We demonstrate that the fuel volume flow rate and the equivalence ratio play different but critical roles on generating thermoacoustic instability at different frequencies and amplitudes. Maximum sound pressure level can be as high as 135 dB. In addition, mode switching, (i.e. frequency swap) is found to occur between approximately ω 3 ≈ 510 Hz and ω 1 ≈ 170 Hz, depending on the equivalence ratio ϕ. Furthermore, the dominant frequency corresponding to the maximum amplitude is shown to be shifted by approximately 20%, as the fuel flow rate V f is increased and the combustion condition is changed from lean to rich. These findings are quite useful for designing a feedback control strategy to stabilize an unstable combustor. The present work opens up an applicable means to design a stable swirling combustor.

“…Passive control techniques generally involves modifying the structure of combustor by installing acoustic damper such as perforated liners or resonators. However, modifying the combustion system can be high-cost, inefficient and lack of flexibility [10]. Recently, alternative methods have recently been proposed and investigated besides the classical active and passive control methods.…”

Section: Introductionmentioning

confidence: 99%

Numerical Study of Nonlinear Self-sustained Thermoacoustic Instability in a Swirling Combustor

Sun

AIAA Propulsion and Energy 2020 Forum

2020

Self-exited thermoacoustic instability is undesirable in gas turbines and other propulsion systems due to structural vibration, overheating and flame flashback. Such instability is characterized with large-amplitude limit cycle oscillations. It is typically resulting from the dynamic interaction between turbulence flow-flame-acoustics. A better understanding on the interaction, and an alternative design of effective damping/control approach to stabilize combustors are wanted. In this work, 3D numerical simulations are conducted on a swirling combustor to gain insight on the generation of nonlinear swirling flow-flame-coupled thermoacoustic instability. To capture the turbulence flow-combustion-acoustics interaction, the classical turbulence model for swirling flow RNG k-ε and eddy dissipation concept model with 2-steps are applied. The model is validated first with the experimental data available in the literature. Then it is applied to study the effect of swirling number SN. It is found that increasing the SN leads to the amplitude of combustion instability being increased. The dominant frequency is found to shift to a higher value with increased SN. To attenuate the selfexcited thermoacoustic instability, we propose an alternative passive control approach by implementing a heat exchanger at a pre-selected segment of combustor wall; its temperature TH could be varied. Numerical results show that properly setting TH can attenuate the thermoacoustic instability by approximately 20 dB. The present study contributes to developing a platform to simulate nonlinear thermoacoustic instability in a swirling combustor. It also opens up an alternative control means to prevent the onset or attenuate the undesirable limit cycle oscillations.