Response of Autoignition-Stabilized Flames to One-Dimensional Disturbances: Intrinsic Response

2021 ◽  
Author(s):  
Harish Subramanian Gopalakrishnan ◽  
Andrea Gruber ◽  
Jonas Moeck
Keyword(s):  
Flame Front ◽  
Acoustic Waves ◽  
Gas Turbines ◽  
Temperature Fluctuations ◽  
Feedback Mechanism ◽  
Stable Operation ◽  
One Dimensional ◽  
Flame Response ◽  
Mean Pressure ◽  
Stabilized Flames

Abstract Burning carbon-free fuels such as hydrogen in gas turbines promises power generation with reduced greenhouse gas emissions. A two-stage combustor architecture with an autoignition-stabilized flame in the second stage allows for efficient combustion of hydrogen fuels. However, interactions between the autoignition-stabilized flame and the acoustic field of the combustor may result in self-sustained oscillations of the flame front position and heat release rate, which severely affect the stable operation of the combustor. We study one such 'intrinsic' mode of interaction wherein acoustic waves generated by the unsteady flame travel upstream and modulate the incoming mixture resulting in flame front oscillations. In particular, we study the response of an autoignition-stabilized flame to upstream traveling acoustic disturbances in a one-dimensional configuration. We first present a numerical framework to calculate the response of autoignition-stabilized flames to acoustic and entropy disturbances in a one-dimensional combustor. The flame response is computed by solving the energy and species mass balance equations. We validate the framework with compressible direct numerical simulations. Lastly, we present results for the flame response to upstream traveling acoustic perturbations. The results show that autoignition-stabilized flames are highly sensitive to acoustic temperature fluctuations and exhibit a characteristic frequency-dependent response. Acoustic pressure and velocity fluctuations constructively or destructively superpose with temperature fluctuations, depending on the mean pressure and relative phase between the fluctuations. The findings of the present work are essential for understanding the intrinsic feedback mechanism in combustors with autoignition-stabilized flames.

Response of Autoignition-Stabilized Flames to One-Dimensional Disturbances: Intrinsic Response

2021 ◽  
Author(s):  
Harish S. Gopalakrishnan ◽  
Andrea Gruber ◽  
Jonas Moeck
Keyword(s):  
Flame Front ◽  
Acoustic Waves ◽  
Gas Turbines ◽  
Temperature Fluctuations ◽  
Feedback Mechanism ◽  
Stable Operation ◽  
Detailed Chemistry ◽  
One Dimensional ◽  
Flame Response ◽  
Stabilized Flames

Abstract Burning carbon-free fuels such as hydrogen in gas turbines promises power generation with strongly reduced greenhouse gas emissions. A two-stage combustor architecture with a propagation-stabilized flame in the first stage and an autoignition-stabilized flame in the second stage allows for efficient combustion of hydrogen fuels. However, interactions between the autoignition-stabilized flame and the acoustic field of the combustor may result in self-sustained oscillations of the flame front position and heat release rate, which severely affect the stable operation of the combustor. We study one such ‘intrinsic’ mode of interaction wherein acoustic waves generated by the unsteady flame front travel upstream and modulate the incoming mixture resulting in flame front oscillations. In particular, we study the response of an autoignition-stabilized flame to upstream traveling acoustic disturbances in a simplified one-dimensional configuration. We first present a numerical framework to calculate the response of autoignition-stabilized flames to acoustic and entropy disturbances in a one-dimensional combustor. The flame response is computed by solving the energy and species mass balance equations, coupled with detailed chemistry. We validate the framework with compressible direct numerical simulations. Lastly, we present results for the flame response to upstream traveling acoustic perturbations. The results show that autoignition-stabilized flames are highly sensitive to acoustic temperature fluctuations and exhibit a characteristic frequency-dependent response. Acoustic pressure and velocity fluctuations can either constructively or destructively superpose with temperature fluctuations, depending on the mean pressure and relative phase between the fluctuations. The findings of the present work are essential for understanding and modeling the intrinsic feedback mechanism in combustors with autoignition-stabilized flames.

scholarly journals Resonant excitation of acoustic waves in one-dimensional exciton-polariton systems

2019 ◽  
Vol 100 (4) ◽  
Author(s):  
A. V. Yulin ◽  
V. K. Kozin ◽  
A. V. Nalitov ◽  
I. A. Shelykh
Keyword(s):  
Acoustic Waves ◽  
Resonant Excitation ◽  
One Dimensional

Models of the scalar spectrum for turbulent advection

1978 ◽  
Vol 88 (3) ◽  
pp. 541-562 ◽  
Author(s):  
R. J. Hill
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Schmidt Number ◽  
Temperature Fluctuations ◽  
Limited Extent ◽  
Temperature Spectrum ◽  
One Dimensional ◽  
Moderate Reynolds Number ◽  
Temperature Spectra ◽  
High Reynolds

Several models are developed for the high-wavenumber portion of the spectral transfer function of scalar quantities advected by high-Reynolds-number, locally isotropic turbulent flow. These models are applicable for arbitrary Prandtl or Schmidt number, v/D, and the resultant scalar spectra are compared with several experiments having different v/D. The ‘bump’ in the temperature spectrum of air observed over land is shown to be due to a tendency toward a viscous-convective range and the presence of this bump is consistent with experiments for large v/D. The wavenumbers defining the transition between the inertial-convective range and viscous-convective range for asymptotically large v/D (denoted k* and k1* for the three- and one-dimensional spectra) are determined by comparison of the models with experiments. A measurement of the transitional wavenumber k1* [denoted (k1*)s] is found to depend on v/D and on any filter cut-off. On the basis of the k* values it is shown that measurements of β1 from temperature spectra in moderate Reynolds number turbulence in air (v/D = 0·72) maybe over-estimates and that the inertial-diffusive range of temperature fluctuations in mercury (v/D ≃ 0·02) is of very limited extent.

Dynamic Simulation of Full Start-Up Procedure of Heavy Duty Gas Turbines

2001 ◽  
Author(s):  
J. H. Kim ◽  
T. W. Song ◽  
T. S. Kim ◽  
S. T. Ro
Keyword(s):  
Gas Turbines ◽  
Guide Vane ◽  
Inlet Guide Vane ◽  
Stable Operation ◽  
Heavy Duty ◽  
Operating Characteristics ◽  
Fully Implicit ◽  
Start Up ◽  
Full Speed ◽  
Stage Characteristic

A simulation program for transient analysis of the start-up procedure of heavy duty gas turbines for power generation has been constructed. Unsteady one-dimensional conservation equations are used and equation sets are solved numerically using a fully implicit method. A modified stage-stacking method has been adopted to estimate the operation of the compressor. Compressor stages are grouped into three categories (front, middle, rear), to which three different stage characteristic curves are applied in order to consider the different low-speed operating characteristics. Representative start-up sequences were adopted. The dynamic behavior of a representative heavy duty gas turbine was simulated for a full start-up procedure from zero to full speed. Simulated results matched the field data and confirmed unique characteristics such as the self-sustaining and the possibility of rear-stage choking at low speeds. Effects of the estimated schedules on the start-up characteristics were also investigated. Special attention was paid to the effects of modulating the variable inlet guide vane on start-up characteristics, which play a key role in the stable operation of gas turbines.

The Effect of Transient Fuel Staging on Self-Excited Instabilities in a Multi-Nozzle Model Gas Turbine Combustor

2017 ◽  
Author(s):  
Wyatt Culler ◽  
Janith Samarasinghe ◽  
Bryan D. Quay ◽  
Domenic A. Santavicca ◽  
Jacqueline O’Connor
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
High Speed ◽  
Equivalence Ratio ◽  
Growth Time ◽  
Stable Operation ◽  
Time Constants ◽  
Decay Times ◽  
Fuel Staging ◽  
Passive Techniques

Combustion instability in gas turbines can be mitigated using active techniques or passive techniques, but passive techniques are almost exclusively used in industrial settings. While fuel staging, a common passive technique, is effective in reducing the amplitude of self-excited instabilities in gas turbine combustors at steady-state conditions, the effect of transients in fuel staging on self-excited instabilities is not well understood. This paper examines the effect of fuel staging transients on a laboratory-scale five-nozzle can combustor undergoing self-excited instabilities. The five nozzles are arranged in a four-around-one configuration and fuel staging is accomplished by increasing the center nozzle equivalence ratio. When the global equivalence ratio is φ = 0.70 and all nozzles are fueled equally, the combustor undergoes self-excited oscillations. These oscillations are suppressed when the center nozzle equivalence ratio is increased to φ = 0.80 or φ = 0.85. Two transient staging schedules are used, resulting in transitions from unstable to stable operation, and vice-versa. It is found that the characteristic instability decay times are dependent on the amount of fuel staging in the center nozzle. It is also found that the decay time constants differ from the growth time constants, indicating hysteresis in stability transition points. High speed CH* chemiluminescence images in combination with dynamic pressure measurements are used to determine the instantaneous phase difference between the heat release rate fluctuation and the combustor pressure fluctuation throughout the combustor. This analysis shows that the instability onset process is different from the instability decay process.

Flame Characteristics and Turbulent Flame Speeds of Turbulent, High-Pressure, Lean Premixed Methane/Air Flames

2005 ◽  
Author(s):  
P. Griebel ◽  
R. Bombach ◽  
A. Inauen ◽  
R. Scha¨ren ◽  
S. Schenker ◽  
...  
Keyword(s):  
Flame Front ◽  
Gas Turbines ◽  
Equivalence Ratio ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Operating Conditions ◽  
Turbulent Flame Speed ◽  
Front Position ◽  
Preheating Temperature ◽  
Lean Premixed

The present experimental study focuses on flame characteristics and turbulent flame speeds of lean premixed flames typical for stationary gas turbines. Measurements were performed in a generic combustor at a preheating temperature of 673 K, pressures up to 14.4 bars (absolute), a bulk velocity of 40 m/s, and an equivalence ratio in the range of 0.43–0.56. Turbulence intensities and integral length scales were measured in an isothermal flow field with Particle Image Velocimetry (PIV). The turbulence intensity (u′) and the integral length scale (LT) at the combustor inlet were varied using turbulence grids with different blockage ratios and different hole diameters. The position, shape, and fluctuation of the flame front were characterized by a statistical analysis of Planar Laser Induced Fluorescence images of the OH radical (OH-PLIF). Turbulent flame speeds were calculated and their dependence on operating conditions (p, φ) and turbulence quantities (u′, LT) are discussed and compared to correlations from literature. No influence of pressure on the most probable flame front position or on the turbulent flame speed was observed. As expected, the equivalence ratio had a strong influence on the most probable flame front position, the spatial flame front fluctuation, and the turbulent flame speed. Decreasing the equivalence ratio results in a shift of the flame front position farther downstream due to the lower fuel concentration and the lower adiabatic flame temperature and subsequently lower turbulent flame speed. Flames operated at leaner equivalence ratios show a broader spatial fluctuation as the lean blow-out limit is approached and therefore are more susceptible to flow disturbances. In addition, because of a lower turbulent flame speed these flames stabilize farther downstream in a region with higher velocity fluctuations. This increases the fluctuation of the flame front. Flames with higher turbulence quantities (u′, LT) in the vicinity of the combustor inlet exhibited a shorter length and a higher calculated flame speed. An enhanced turbulent heat and mass transport from the recirculation zone to the flame root location due to an intensified mixing which might increase the preheating temperature or the radical concentration is believed to be the reason for that.

Zener tunneling of acoustic waves in a one-dimensional phononic crystal

2007 ◽  
Vol 144 (10-11) ◽  
pp. 433-436 ◽  
Author(s):  
Zhaojian He ◽  
Shasha Peng ◽  
Yun Wang ◽  
Manzhu Ke ◽  
Zhengyou Liu
Keyword(s):  
Acoustic Waves ◽  
Phononic Crystal ◽  
One Dimensional ◽  
Zener Tunneling
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