On scalar dissipation and partially premixed flame propagation

2003 ◽  
Vol 175 (4) ◽  
pp. 649-664 ◽  
Author(s):  
K.A. Watson ◽  
K.M. Lyons ◽  
J.M. Donbar ◽  
C.D. Carter
Keyword(s):  
Flame Propagation ◽  
Premixed Flame ◽  
Scalar Dissipation ◽  
Partially Premixed ◽  
Partially Premixed Flame

Effect of Acoustic Feedback on Lagrangian Coherent Structures in a Backward Facing Step Combustor With a Partially Premixed Flame

2017 ◽  
Author(s):  
Ramgopal Sampath ◽  
S. R. Chakravarthy
Keyword(s):  
Coherent Structures ◽  
Large Scale ◽  
Pressure Oscillation ◽  
Velocity Fields ◽  
Premixed Flame ◽  
Time Resolved ◽  
Acoustic Feedback ◽  
Acoustic Characterization ◽  
Partially Premixed ◽  
Partially Premixed Flame

The thermoacoustic oscillations of a partially premixed flame stabilized in a backward facing step combustor are studied at a constant equivalence ratio in long and short combustor configurations corresponding to with and without acoustic feedback respectively. We perform simultaneous time-resolved particle image velocimetry (TR-PIV) and chemiluminescence for selected flow conditions based on the acoustic characterization in the long combustor. The acoustic characterization shows a transition in the dominant pressure amplitudes from low to high magnitudes with an increase in the inlet flow Reynolds number. This is accompanied by a shift in the dominant frequencies. For the intermittent pressure oscillations in the long combustor, the wavelet analysis indicates a switch between the acoustic and vortex modes with silent zones of relatively low-pressure amplitudes. The short combustor configuration indicates the presence of the vortex shedding frequency and an additional band comprising the Kelvin Helmholtz mode. Next, we apply the method of finite-time Lyapunov exponent (FTLE) to the time-resolved velocity fields to extract features of the Lagrangian coherent structures (LCS) of the flow. In the long combustor post transition with the time instants with dominant acoustic mode, a large-scale modulation of the FTLE boundaries over one cycle of pressure oscillation is evident. Further, the FTLEs and the flame boundaries align each other for all phases of the pressure oscillation. In the short combustor, the FTLEs indicate the presence of small wavelength waviness that overrides the large-scale vortex structure, which corresponds to the vortex shedding mode. This behaviour contrasts with the premixed flame in the short combustor reported earlier in which such large scales were found to be seldom present. The presence of the large-scale structures even in the absence of acoustic feedback in a partially premixed flame signifies its inherent unstable nature leading to large pressure amplitudes during acoustic feedback. Lastly, the FTLE boundaries provide the frequency information of the identified coherent structure and also acts as the surrogate flame boundaries that are estimated from just the velocity fields.

Modeling Unsteady Flow of a Lean Partially Premixed Flame on a Dry Low NOx Combustion System

2013 ◽  
Author(s):  
Salvatore Matarazzo ◽  
Hannes Laget ◽  
Evert Vanderhaegen ◽  
Jim B. W. Kok
Keyword(s):  
Gas Turbine ◽  
Limit Cycle ◽  
Gas Turbines ◽  
Premixed Flame ◽  
Computational Domain ◽  
Pressure Oscillations ◽  
Combustion Dynamics ◽  
Partially Premixed ◽  
Partially Premixed Flame ◽  
Limit Cycle Behavior

The phenomenon of combustion dynamics (CD) is one of the most important operational challenges facing the gas turbine (GT) industry today. The Limousine project, a Marie Curie Initial Training network funded by the European Commission, focuses on the understanding of the limit cycle behavior of unstable pressure oscillations in gas turbines, and on the resulting mechanical vibrations and materials fatigue. In the framework of this project, a full transient CFD analysis for a Dry Low NOx combustor in a heavy duty gas turbine has been performed. The goal is to gain insight on the thermo-acoustic instability development mechanisms and limit cycle oscillations. The possibility to use numerical codes for complex industrial cases involving fuel staging, fluid-structure interaction, fuel quality variation and flexible operations has been also addressed. The unsteady U-RANS approach used to describe the high-swirled lean partially premixed flame is presented and the results on the flow characteristics as vortex core generation, vortex shedding, flame pulsation are commented on with respect to monitored parameters during operations of the GT units at Electrabel/GDF-SUEZ sites. The time domain pressure oscillations show limit cycle behavior. By means of Fourier analysis, the coupling frequencies caused by the thermo-acoustic feedback between the acoustic resonances of the chamber and the flame heat release has been detected. The possibility to reduce the computational domain to speed up computations, as done in other works in literature, has been investigated.

H2/CO/air premixed and partially premixed flame structure at different pressures based on reaction limit analysis

2018 ◽  
Vol 63 (19) ◽  
pp. 1260-1266 ◽  
Author(s):  
Zaigang Liu ◽  
Wenjun Kong ◽  
Jean-Louis Consalvi ◽  
Wenhu Han
Keyword(s):  
Limit Analysis ◽  
Flame Structure ◽  
Premixed Flame ◽  
Partially Premixed ◽  
Partially Premixed Flame
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