Premixed Swirling Flame Response to Acoustic Forcing Studied With High-Speed PIV and OH* Chemiluminescence

2015 ◽  
Author(s):  
Alexey Denisov ◽  
Abhishek Ravi
Keyword(s):  
Heat Release ◽  
High Speed ◽  
Decomposition Analysis ◽  
Acoustic Oscillations ◽  
Acoustic Frequency ◽  
Precessing Vortex Core ◽  
Technological Advances ◽  
Flame Response ◽  
Swirling Flame ◽  
Acoustic Forcing

Studies of swirling flames have been boosted by technological advances in high-speed lasers and cameras. Temporal and spatial evolution of swirling flows has been revealed by high-speed particle image velocimetry (PIV). We have studied the response of a perfectly premixed swirling flame to weak acoustic perturbations induced by a pair of loudspeakers upstream of the burner. Phase-resolved response of the flame was observed with PIV and OH* chemiluminescence measurements running at 12 times the forcing frequency. The flow dynamics was not affected by the flame compared to non-reacting conditions and the flame responded to flow variations by changing its angle. Proper orthogonal decomposition analysis revealed that the strongest coherent structure in the flow was precessing vortex core that caused transversal variation of the heat release without producing acoustic oscillations. Axisymmetric vortices were not observed at this level of acoustic forcing, but precession modes were modulated at acoustic frequency as additional frequency peaks appeared at the sum and the difference of precession and forcing frequencies. Average time of vortex convection from the burner to the flame is close to the delay of the flame response to acoustic forcing, measured by microphones. This supports the importance of vortex propagation to acoustic modulation of flame heat release.

scholarly journals Studies of the Precessing Vortex Core in Swirling Flows

2012 ◽  
Vol 10 (5) ◽  
Author(s):  
M.O. Vigueras-Zuñiga ◽  
A. Valera-Medina ◽  
N. Syred
Keyword(s):  
Vortex Core ◽  
High Speed ◽  
Large Scale ◽  
Combustion Regime ◽  
Complex Nature ◽  
High Speed Photography ◽  
Acoustic Oscillations ◽  
Lean Premixed Combustion ◽  
Precessing Vortex Core ◽  
Different Types

Large scale coherent structures play an important role in the behavior of the combustion regime inside any type ofcombustor stabilized by swirl, with special impact on factors such as flame stability, blow off, emissions and theoccurrence of thermo-acoustic oscillations. Lean premixed combustion is widely used and is known to impact many ofthese factors, causing complex interrelationships with any coherent structure formed. Despite the extensiveexperimentation in this matter, the above phenomena are poorly understood. Numerical simulations have been usedto try to explain the development of different regimes, but their extremely complex nature and lack of time dependentvalidation show varied and debatable results. The precessing vortex core (PVC) is a well-known coherent structurewhose development, intensity and occurrence has not been well documented. This paper thus adopts an experimentalapproach to characterize the PVC in a simple swirl burner under combustion conditions so as to reveal the effects ofswirl and other variables on the latter. Aided by a high speed photography (HSP) system, the recognition and extentof several different types of PVCs were observed and discussed.

Acoustic Perturbation Effects on the Fluid Dynamics and Swirling Flame Response in a Non-Premixed Co-Flow Burner

2010 ◽  
Author(s):  
Uyi Idahosa ◽  
Abhishek Saha ◽  
Navid Khatami ◽  
Chengying Xu ◽  
Saptarshi Basu
Keyword(s):  
Heat Release ◽  
Low Frequency ◽  
Ccd Camera ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Fuel Flow ◽  
Flame Dynamics ◽  
Flame Response ◽  
Low Pass ◽  
Swirling Flame

An investigation into the response of non-premixed swirling flames to acoustic perturbations at various frequencies (fp = 0–315 Hz) and swirl intensities (S = 0.09 and 0.34) is carried out. Perturbations are generated using a loudspeaker at the base of an atmospheric co-flow burner with resulting velocity oscillation amplitudes |u′/Uavg| in the 0.03–0.30 range. The dependence of flame dynamics on the relative richness of the flame is investigated by studying various constant fuel flow rate flame configurations. Flame heat release is quantitatively measured and simultaneously imaged using a photomultiplier (PMT) and a phase-locked CCD camera. Both of which are fitted with 430nm bandpass filters for observing CH*chemiluminescence. The flame response is observed to exhibit a low-pass filter characteristic with minimal flame response beyond pulsing frequencies of 200Hz. Flames at lower fuel flow rates are observed to remain attached to the central fuel pipe at all acoustic pulsing frequencies. PIV imaging of the associated isothermal fields show the amplification in flame aspect ratio is caused by the narrowing of the inner recirculation zone (IRZ). The Rayleigh criterion (R) is used to assess the potential for instability of specific perturbation configurations and is found to be a good predictor of unstable modes. Phase conditioned analysis of the flame dynamics yield additional criteria in highly responsive modes to include the effective amplitude of velocity oscillations induced by the acoustic pulsing. Highly amplified responses were observed in pulsed flame configurations with Strouhal numbers (St = fpUavg/dm) in the 1–3.5 range. Heat release to velocity perturbation time delays on the order of the acoustic pulsing period also characterized the highly responsive flames. Finally, wavelet analyses of heat release perturbations indicate sustained low frequency oscillations that become more prominent for low acoustic pulsing frequencies in lean flame configurations.

Direct Numerical Simulation Study of Premixed Flame Response to Fuel-Air Ratio Oscillations

2011 ◽  
Author(s):  
Santosh Hemchandra
Keyword(s):  
Heat Release ◽  
Equivalence Ratio ◽  
Flame Length ◽  
Acoustic Oscillations ◽  
Lean Premixed Combustion ◽  
Fuel Injectors ◽  
Reduced Order ◽  
Hydrodynamic Coupling ◽  
Flame Response ◽  
Mass Flow Rates

The coupling between heat release oscillations produced by equivalence ratio fluctuations with combustor acoustic modes in lean premixed combustion systems, is a serious problem that limits the operation envelope of these devices. Such oscillations are produced by an oscillating pressure drop across air inlets and/or fuel injectors due to the presence of acoustic oscillations. This results in fluctuations in mass flow rates of air and/or fuel entering the combustor, thereby, changing the local equivalence ratio of the mixture at these injector/inlet locations. These perturbations in equivalence ratio are advected by the flow into the flame, causing its heat release to oscillate. Detailed reduced order models for the heat release response of premixed flames to equivalence ratio oscillations, based on this phenomenological picture, have been developed in the past. A key problem in validating these models is the ambiguity of interpretation of chemiluminescence signals when, the length scale of equivalence ratio fluctuations is smaller than the characteristic flame length. As such, the present work performs a DNS of a premixed methane-air flame, subject to unsteady forcing in upstream methane mass fraction. Predictions from prior reduced order modelling approaches are compared with present DNS results. The agreement between modelling and DNS predictions in the characteristics of flame response is good at low excitation frequencies and amplitudes. This agreement, however, degrades as forcing amplitude and frequency increase due to the influence of hydrodynamic coupling between the flow-fields on either side of the flame as well as damping of equivalence ratio perturbations by diffusion, on the dynamics of the flame.

Nonlinear Heat-Release/Acoustic Interactions in a Gas Turbine Combustor

2004 ◽  
Author(s):  
Ben Bellows ◽  
Tim Lieuwen
Keyword(s):  
Transfer Function ◽  
Heat Release ◽  
Gas Turbines ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Amplitude Dependence ◽  
Acoustic Oscillations ◽  
Bunsen Flame ◽  
Flame Response ◽  
Acoustic Transfer Function

This paper describes an experimental investigation of the response of the flame in a lean, premixed combustor to imposed acoustic oscillations. The ultimate objective of this work is to develop capabilities for predicting the amplitude of combustion instabilities in gas turbines. Simultaneous measurements of CH* and OH* chemiluminescence, pressure, and velocity were obtained over a range of forcing amplitudes and frequencies. These data show that nonlinearity in the heat release/acoustic transfer function is manifested in two ways. First, the flame chemiluminescence response to imposed oscillations saturates at pressure and velocity amplitudes on the order of p’/po ∼0.02 and u’/uo∼0.3. In addition, the phase between the CH* or OH* oscillations and acoustic oscillations exhibits some amplitude dependence, even at disturbance amplitudes where the amplitude transfer function is linear. We also find that the response of this swirling, highly turbulent flame exhibits similarities to those of simple, laminar flame configurations. First, the “linear”, low amplitude flame response is similar to the laminar, V-flame measurements and predictions of Schuller et al. [1]. Also, at large disturbance amplitudes, the subharmonic characteristics of the oscillations exhibit analogous characteristics to those observed by Bourehla & Baillot [2] in a conical Bunsen flame, and Searby & Rochwerger [3] in a flat flame.

High-speed simultaneous PLIF/PIV imaging of a lift-off swirling flame under acoustic forcing

2021 ◽  
Vol 121 ◽  
pp. 110259
Author(s):  
Xunchen Liu ◽  
Sirui Wang ◽  
Guoqing Wang ◽  
Liangliang Xu ◽  
Lei Li
Keyword(s):  
High Speed ◽  
Swirling Flame ◽  
Acoustic Forcing ◽  
Lift Off

Flame Leading Edge and Flow Dynamics in a Swirling, Lifted Flame

2012 ◽  
Author(s):  
Michael Malanoski ◽  
Michael Aguilar ◽  
Jacqueline O’Connor ◽  
Dong-hyuk Shin ◽  
Bobby Noble ◽  
...  
Keyword(s):  
Heat Release ◽  
Shear Layer ◽  
High Speed ◽  
Vortex Breakdown ◽  
Leading Edge ◽  
Flame Stabilization ◽  
Stagnation Points ◽  
Flow Stagnation ◽  
Flame Response ◽  
Stabilized Flames

Flames in high swirl flow fields with vortex breakdown often stabilize aerodynamically in front of interior flow stagnation points. In contrast to shear layer stabilized flames with a nearly fixed, well defined flame attachment point, the leading edge of aerodynamically stabilized flames can move around substantially, due to both the inherent dynamics of the vortex breakdown region, as well as externally imposed oscillations. Motion of this flame stabilization point relative to the flow field has an important dynamical role during combustion instabilities, as it creates flame front wrinkles and heat release fluctuations. For example, a prior study has shown that nonlinear dynamics of the flame response at high forcing amplitudes were related to these leading edge dynamics. This heat release mechanism exists alongside other flame wrinkling processes, arising from such processes as shear layer rollup and swirl fluctuations. This paper describes an experimental investigation of acoustic forcing effects on the dynamics of leading edge of a swirl stabilized flame. Vortex breakdown bubble dynamics were characterized using both high-speed particle image velocimetry (PIV) and line-of-sight high-speed CH* chemiluminescence. A wide array of forcing conditions was achieved by varying forcing frequency, amplitude, and acoustic field symmetry. These results show significant differences in instantaneous and time averaged location of the flow stagnation points. They also show motion of the flame leading edge that are of the same order of magnitude as corresponding particle displacement associated with the fluctuating velocity field. This observation suggests that heat release fluctuations associated with leading edge motion may be just as significant in controlling the unsteady flame response as the flame wrinkles excited by velocity fluctuations.

Dynamics of a Transversely Excited Swirling, Lifted Flame: Part I — Experiments and Data Analysis

2013 ◽  
Author(s):  
Michael Malanoski ◽  
Michael Aguilar ◽  
Vishal Acharya ◽  
Tim Lieuwen
Keyword(s):  
High Speed ◽  
Acoustic Excitation ◽  
Response Model ◽  
Combustion Instabilities ◽  
Excitation Field ◽  
Azimuthal Mode ◽  
Flow Response ◽  
Flame Response ◽  
Swirling Flame ◽  
Helical Mode

This paper is the first of two parts, and describes measurements of the response of a transversely forced, single nozzle, swirling flame. This study is motivated by combustion instabilities coupling with azimuthal combustor modes. Two different forcing configurations are applied, where the flame/nozzle are located at a pressure node and anti-node, respectively. High speed velocimetry and chemiluminescence measurements were made of the forced and unforced flow in multiple orthogonal planes, revealing both the axial and azimuthal development of the unsteady flow. Spectra and azimuthal mode decompositions of these data show the dominance of the m = 1 helical mode in the unforced flow. Depending upon the nature of the forcing, the flow response at the forcing frequency can be dominated by the axisymmetric, m = 0 mode, or the m = 1 mode. These results clearly show that the dominant fluid mechanic structures exciting flames during transverse instabilities varies from nozzle to nozzle, depending upon the phase characteristics of the acoustic excitation field. Part II of this paper uses these time averaged and fluctuating measurements as inputs to a flame response model of the unsteady global heat release fluctuations.

Nonlinear interaction between a precessing vortex core and acoustic oscillations in a turbulent swirling flame

2012 ◽  
Vol 159 (8) ◽  
pp. 2650-2668 ◽  
Author(s):  
Jonas P. Moeck ◽  
Jean-François Bourgouin ◽  
Daniel Durox ◽  
Thierry Schuller ◽  
Sébastien Candel
Keyword(s):  
Nonlinear Interaction ◽  
Vortex Core ◽  
Acoustic Oscillations ◽  
Precessing Vortex Core ◽  
Swirling Flame

scholarly journals Wall Temperature Measurements in Gas Turbine Combustors With Thermographic Phosphors

2018 ◽  
Vol 141 (4) ◽  
Author(s):  
Patrick Nau ◽  
Zhiyao Yin ◽  
Oliver Lammel ◽  
Wolfgang Meier
Keyword(s):  
Gas Turbine ◽  
Wall Temperature ◽  
Gas Turbines ◽  
High Speed ◽  
Bluff Body ◽  
Temperature Measurements ◽  
Transient Temperature ◽  
High Time Resolution ◽  
Ceramic Surface ◽  
Precessing Vortex Core

Phosphor thermometry has been developed for wall temperature measurements in gas turbines and gas turbine model combustors. An array of phosphors has been examined in detail for spatially and temporally resolved surface temperature measurements. Two examples are provided, one at high pressure (8 bar) and high temperature and one at atmospheric pressure with high time resolution. To study the feasibility of this technique for full-scale gas turbine applications, a high momentum confined jet combustor at 8 bar was used. Successful measurements up to 1700 K on a ceramic surface are shown with good accuracy. In the same combustor, temperatures on the combustor quartz walls were measured, which can be used as boundary conditions for numerical simulations. An atmospheric swirl-stabilized flame was used to study transient temperature changes on the bluff body. For this purpose, a high-speed setup (1 kHz) was used to measure the wall temperatures at an operating condition where the flame switches between being attached (M-flame) and being lifted (V-flame) (bistable). The influence of a precessing vortex core (PVC) present during M-flame periods is identified on the bluff body tip, but not at positions further inside the nozzle.

Soot evolution and flame response to acoustic forcing of laminar non-premixed jet flames at varying amplitudes

2018 ◽  
Vol 198 ◽  
pp. 249-259 ◽  
Author(s):  
Kae Ken Foo ◽  
Zhiwei Sun ◽  
Paul R. Medwell ◽  
Zeyad T. Alwahabi ◽  
Graham J. Nathan ◽  
...  
Keyword(s):  
Jet Flames ◽  
Flame Response ◽  
Acoustic Forcing
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