Transformation of Transverse Acoustic Velocity of the Burner Approach Flow Into Flame Dynamics

2012 ◽  
Author(s):  
Martin Hauser ◽  
Michael Wagner ◽  
Thomas Sattelmayer
Keyword(s):  
Acoustic Field ◽  
Velocity Fluctuation ◽  
Gas Turbines ◽  
Transverse Velocity ◽  
Excitation Frequency ◽  
Rotational Flow ◽  
Acoustic Oscillations ◽  
Flow Oscillation ◽  
Low Frequencies ◽  
The Stability

Modern, large gas turbines for power generation have multiple burners, which are distributed around the circumference of the engine and which generate flames in combustors of either annular or can-annular geometry. In both cases considering only the axial modes has proven to be insufficient for the assessment of the thermoacoustic stability. An adequate analysis requires consideration of the circumferential acoustic coupling, generated by the acoustic field in the upstream and downstream annuli and the open passages between the cans, respectively. As in annular combustors the particularly critical eigenmodes with low frequencies are predominantly of circumferential nature, the stability of annular combustors is often governed by the onset of circumferential acoustic oscillations. In this study one single radial swirl burner is exposed to a transverse velocity fluctuation comparable to a circumferential oscillation in the plenum annulus. The transverse velocity fluctuation is transformed into a rotational flow oscillation through a convective process depending on excitation frequency and mass flow rate. The characteristics of this process are determined and the resulting dynamic flow structure in the burner nozzle is analyzed. Phase plots show that the rotational flow oscillation is transported into the flame causing a rotational flame pulsation. The influence of transverse velocity fluctuation on the global dynamic flame behavior is determined through FTF measurements. It is concluded from the increased FTF amplitude observed for transverse velocity excitation that the modification of the acoustic field at the burner exit due to circumferential acoustic modes has to be taken into account for a reliable prediction of the stability limits of annular gas turbines.

Influence of Transversal Acoustic Excitation of the Burner Approach Flow on the Flame Structure

2010 ◽  
Vol 133 (4) ◽  
Author(s):  
Martin Hauser ◽  
Manuel Lorenz ◽  
Thomas Sattelmayer
Keyword(s):  
Combustion Chamber ◽  
Acoustic Field ◽  
Gas Turbines ◽  
Phase Distribution ◽  
Flame Structure ◽  
Excitation Frequency ◽  
Acoustic Properties ◽  
Acoustic Oscillations ◽  
Test Rig ◽  
Low Frequencies

Modern large gas turbines for power generation have multiple burners, which are distributed around the circumference of the engine and which generate flames in combustors of either annular or can-annular geometry. In both cases, considering only the axial modes has proven to be insufficient for the assessment of the thermoacoustic stability. An adequate analysis requires consideration of the circumferential acoustic coupling generated by the acoustic field in the upstream and downstream annuli and the open passages between the cans, respectively. As in annular combustors, the particularly critical eigenmodes with low frequencies are predominantly of circumferential nature; the stability of annular combustors is often governed by the onset of circumferential acoustic oscillations. To determine the influence of these circumferential acoustic modes on the dynamic flame behavior, a new single burner test rig was developed. The unique acoustic properties of the test rig allow the exposure of a single swirl burner to a two-dimensional acoustic field that resembles the circumferential mode in an annular combustor. Measurements were performed for axial as well as transversal excitation of the burner and the combination of both. To investigate the dynamic flame structure, phase-resolved flame images have been evaluated in terms of amplitude and phase distribution. Under transversal excitation, the flame structure becomes highly asymmetrical. A region of higher OH∗ intensity is generated in the combustion chamber, which rotates with the excitation frequency. From phase-resolved particle image velocimetry (PIV) measurements of the isothermal flow, it is concluded that the transversal excitation modulates the swirl generation leading to an asymmetrical velocity distribution in the burner nozzle and the combustion chamber.

Influence of Transversal Acoustic Excitation of the Burner Approach Flow on the Flame Structure

2010 ◽  
Author(s):  
Martin Hauser ◽  
Manuel Lorenz ◽  
Thomas Sattelmayer
Keyword(s):  
Combustion Chamber ◽  
Acoustic Field ◽  
Gas Turbines ◽  
Phase Distribution ◽  
Flame Structure ◽  
Excitation Frequency ◽  
Acoustic Properties ◽  
Acoustic Oscillations ◽  
Test Rig ◽  
Low Frequencies

Modern large gas turbines for power generation have multiple burners, which are distributed around the circumference of the engine and which generate flames in combustors of either annular or can-annular geometry. In both cases considering only the axial modes has proven to be insufficient for the assessment of the thermoacoustic stability. An adequate analysis requires consideration of the circumferential acoustic coupling, generated by the acoustic field in the upstream and downstream annuli and the open passages between the cans, respectively. As in annular combustors the particularly critical eigenmodes with low frequencies are predominantly of circumferential nature, the stability of annular combustors is often governed by the onset of circumferential acoustic oscillations. To determine the influence of these circumferential acoustic modes on the dynamic flame behavior, a new single burner test rig was developed. The unique acoustic properties of the test rig allow the exposure of a single swirl burner to a two-dimensional acoustic field that resembles the circumferential mode in an annular combustor. Measurements were performed for axial as well as transversal excitation of the burner and the combination of both. To investigate the dynamic flame structure phase-resolved flame images have been evaluated in terms of amplitude and phase distribution. Under transversal excitation the flame structure becomes highly asymmetrical. A region of higher OH*-intensity is generated in the combustion chamber which rotates with the excitation frequency. From phase-resolved PIV measurements of the isothermal flow it is concluded that the transversal excitation modulates the swirl generation leading to an asymmetrical velocity distribution in the burner nozzle and the combustion chamber, respectively.

Nonparallel Effects on the Stability of Jet Flows

1978 ◽  
Vol 45 (4) ◽  
pp. 717-722 ◽  
Author(s):  
V. K. Garg ◽  
G. F. Round
Keyword(s):  
Transverse Velocity ◽  
Outer Region ◽  
Wave Number ◽  
Jet Flows ◽  
Frequency Range ◽  
Governing Equations ◽  
Low Frequencies ◽  
High Frequencies ◽  
The Stability ◽  
Asymptotic Forms

A theoretical analysis of the linear, spatial stability of Bickley’s jet is presented. The analysis takes into account the effects of transverse velocity component and the axial variations of the basic flow and of the disturbance amplitude, wavenumber and spatial growth rate. The integration of stability equations is started from the outer region of the jet toward the jet axis using the solution of the asymptotic forms of the governing equations. Results are compared with those for the parallel-flow stability analysis. It is found that the nonparallel effects decrease the wave number at low frequencies but increase it at high frequencies. Thus the nonparallel effects make Bickley’s jet unstable over a wider frequency range.

Acoustic Nearfield Characteristics of a Premixed Flame in a Longitudinal Acoustic Field

2001 ◽  
Author(s):  
Doh-Hyoung Lee ◽  
Tim C. Lieuwen
Keyword(s):  
Acoustic Field ◽  
Acoustic Waves ◽  
Near Field ◽  
Premixed Flame ◽  
Acoustic Wave Equation ◽  
Acoustic Oscillations ◽  
Acoustic Characteristics ◽  
Low Frequencies ◽  
Longitudinal Acoustic ◽  
One Dimensional

The occurrence of self excited, combustion driven oscillations pose significant problems in lean, premixed gas turbine combustors. The interactions between flames and longitudinal acoustic oscillations play a key role in many of these instabilities. This paper analyzes the acoustic field in the vicinity of a premixed flame front in order to clarify these interactions. Specifically, it describes a numerical analysis of the acoustic characteristics of a premixed flame that is excited by longitudinal disturbances. Solutions are determined from an integral formulation of the acoustic wave equation that is solved via boundary element techniques. Analyses of these results are performed to characterize the deviations of the acoustic field from one-dimensionality. First, as can be anticipated from quasi one-dimensional considerations, the flame’s reflection coefficient is lower than that predicted by purely one-dimensional calculations. The results also show that the acoustic pressure is nearly one-dimensional in the vicinity of the flame. Finally, they show that the velocity oscillations are strongly multidimensional, even in acoustically compact flames. At very low frequencies, these local velocity oscillations are in phase with each other, while at higher frequencies, their phase may change significantly along the flame. The results of this study show that the multidimensional nature of the acoustic velocity oscillations in the near field of the flame must be taken into consideration in analyses of the interactions between acoustic waves and flames.

Describing the Mechanism of Instability Suppression Using a Central Pilot Flame With Coupled Experiments and Simulations

2021 ◽  
Author(s):  
Jihang Li ◽  
Hyunguk Kwon ◽  
Drue Seksinsky ◽  
Daniel Doleiden ◽  
Jacqueline O’Connor ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Equivalence Ratio ◽  
Vortex Breakdown ◽  
Eddy Simulation ◽  
Breakdown Region ◽  
Large Eddy ◽  
Rate Oscillations ◽  
Combustion Oscillation ◽  
The Stability ◽  
The Impact

Abstract Pilot flames are commonly used to extend combustor operability limits and suppress combustion oscillations in low-emissions gas turbines. Combustion oscillations, a coupling between heat release rate oscillations and combustor acoustics, can arise at the operability limits of low-emissions combustors where the flame is more susceptible to perturbations. While the use of pilot flames is common in land-based gas turbine combustors, the mechanism by which they suppress instability is still unclear. In this study, we consider the impact of a central jet pilot on the stability of a swirl-stabilized flame in a variable-length, single-nozzle combustor. Previously, the pilot flame was found to suppress the instability for a range of equivalence ratios and combustor lengths. We hypothesize that combustion oscillation suppression by the pilot occurs because the pilot provides hot gases to the vortex breakdown region of the flow that recirculate and improve the static, and hence dynamic, stability of the main flame. This hypothesis is based on a series of experimental results that show that pilot efficacy is a strong function of pilot equivalence ratio but not pilot flow rate, which would indicate that the temperature of the pilot gases as well as the combustion intensity of the pilot flame play more of a role in oscillation stabilization than the length of the pilot flame relative to the main flame. Further, the pilot flame efficacy increases with pilot flame equivalence ratio until it matches the main flame equivalence ratio; at pilot equivalence ratios greater than the main equivalence ratio, the pilot flame efficacy does not change significantly with pilot equivalence ratio. To understand these results, we use large-eddy simulation to provide a detailed analysis of the flow in the region of the pilot flame and the transport of radical species in the region between the main flame and pilot flame. The simulation, using a flamelet/progress variable-based chemistry tabulation approach and standard eddy viscosity/diffusivity turbulence closure models, provides detailed information that is inaccessible through experimental measurements.

scholarly journals Application of a three-step approach for prediction of combustion instabilities in industrial gas turbine burners

2017 ◽  
Vol 1 ◽  
pp. JCW78T
Author(s):  
Dmytro Iurashev ◽  
Giovanni Campa ◽  
Vyacheslav V. Anisimov ◽  
Ezio Cosatto ◽  
Luca Rofi ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Time Lag ◽  
High Amplitude ◽  
Combustion Regime ◽  
Industrial Test ◽  
Distributed Model ◽  
Combustion Instabilities ◽  
Acoustic Oscillations ◽  
Analytical Time

Abstract Recently, because of environmental regulations, gas turbine manufacturers are restricted to produce machines that work in the lean combustion regime. Gas turbines operating in this regime are prone to combustion-driven acoustic oscillations referred as combustion instabilities. These oscillations could have such high amplitude that they can damage gas turbine hardware. In this study, the three-step approach for combustion instabilities prediction is applied to an industrial test rig. As the first step, the flame transfer function (FTF) of the burner is obtained performing unsteady computational fluid dynamics (CFD) simulations. As the second step, the obtained FTF is approximated with an analytical time-lag-distributed model. The third step is the time-domain simulations using a network model. The obtained results are compared against the experimental data. The obtained results show a good agreement with the experimental ones and the developed approach is able to predict thermoacoustic instabilities in gas turbines combustion chambers.

scholarly journals Investigating the effect of vibration on the stability of the three-wheeled scooter taxi

2021 ◽  
Vol 39 (4) ◽  
pp. 1117-1122
Author(s):  
S.J. Ojolo ◽  
O.O. Ajayi ◽  
G.A. Asuelinmen
Keyword(s):  
Excitation Frequency ◽  
Vehicle Safety ◽  
Asian Countries ◽  
Wheeled Vehicle ◽  
Safety Margins ◽  
Schematic Layout ◽  
Analysis Design ◽  
The Stability ◽  
The Impact ◽  
Selection Of

The present three wheeled scooter taxi (TWST) that are widespread in Africa and Asian Countries are fuel economical and inexpensive. However, they are unstable due to their schematic layout. This instability places limitation on the usage of the vehicle. Researchers have investigated the rollover and lateral stabilities of this vehicle, including the effect of vibration on the comfort of the riders. However, not much work has been done on the impact of vibration on the stability of the vehicle. These instabilities could be induced by trenches, potholes, uneven and ungraded roads that are prevalent in developing countries. Therefore, this work modelled and analysed the effect of vibration on a TWST using a standard road bump as reference point. The results proved the vehicle to be unstable in the vicinity of excitation frequency of 15.95rad/sec and spring constant of 68,600N/m due to resonance. This would affect safety of life and property. Therefore, it would be appropriate for some of the manufacturers of these vehicles to provide for enough safety margins in the design and selection of springs where the vehicles are rollover and laterally unstable. This will enhance the vehicle safety and receptivity. Keywords: Three wheeled Vehicle, Vibration Modelling and Analysis, Design, Safety of Life and Property

Stochastic Stability of a Universal-Joint Driven Torsional System

1999 ◽  
Author(s):  
S. F. Asokanthan ◽  
Xiao-Hui Wang
Keyword(s):  
Lyapunov Exponent ◽  
Excitation Frequency ◽  
Excitation Amplitude ◽  
Angular Speed ◽  
Analytical Models ◽  
Largest Lyapunov Exponent ◽  
Deterministic Case ◽  
Speed Fluctuation ◽  
The Difference ◽  
The Stability

Abstract Torsional instabilities in a two-degree-of-freedom system driven by a Hooke’s joint due to random input angular speed fluctuation are investigated. Linearised analytical models are used for calculating the largest Lyapunov exponent. Instability behaviour is then characterised by examining the sign of this exponent. Conditions for the onset of instability via sub-harmonic parametric resonances has been shown to coincide with those for the deterministic case. However, the onset of instability via sum as well as the difference type combination resonance is found to be different from that of the deterministic case. The instability conditions for the system under input angular speed fluctuation have been presented graphically in the excitation frequency-excitation amplitude-top Lyapunov exponent space. Predictions for the deterministic and the stochastic cases are compared. The effect of fluctuation probability density as well as that of inertia loads on the stability behaviour of the system has been examined.

Period Motions and Stability in a Nonlinear Spring Pendulum

2018 ◽  
Author(s):  
Albert C. J. Luo ◽  
Yaoguang Yuan
Keyword(s):  
Fourier Series ◽  
Excitation Frequency ◽  
Analytic Method ◽  
Analytical Prediction ◽  
Discrete Fourier Series ◽  
Periodic Motions ◽  
Harmonic Frequency ◽  
Pendulum System ◽  
Nonlinear Spring ◽  
The Stability

In this paper, period-1 motions varying with excitation frequency in a periodically forced, nonlinear spring pendulum system are predicted by a semi-analytic method. The harmonic frequency-amplitude for periodical motions are analyzed from the finite discrete Fourier series. The stability of the periodical solutions are shown on the bifurcation trees as well. From the analytical prediction, numerical illustrations of periodic motions are given, the comparison of numerical solution and analytical solution are given.

scholarly journals Characterization of the Acoustic Interactions in a Two-Staged Multi-Injection Combustor Fed With Liquid Fuel

2012 ◽  
Author(s):  
T. Providakis ◽  
L. Zimmer ◽  
P. Scouflaire ◽  
S. Ducruix
Keyword(s):  
Velocity Field ◽  
Acoustic Field ◽  
Gas Turbines ◽  
High Speed ◽  
Fuel Injection ◽  
Flame Stabilization ◽  
Pollutant Emissions ◽  
Mean Values ◽  
Fuel Distribution ◽  
Droplet Behavior

Burners operating in lean premixed prevaporized (LPP) regimes are considered as good candidates to reduce pollutant emissions from gas turbines. Lean combustion regimes result in lower burnt gas temperatures and therefore a reduction on the NOx emissions, one of the main pollutant species. However, these burners usually show strong flame dynamics, making them prone to various stabilization problems (combustion instabilities, flashback, flame extinction). To face this issue, multi-injection staged combustion can be envisaged. Staging procedures enable fuel distribution control, while multipoint injections can lead to a fast and efficient mixing. A laboratory-scale staged multipoint combustor is developed in the present study, in the framework of LPP combustion, with an injection device close to the industrial one. Using a staging procedure between the primary pilot stage and the secondary multipoint one, droplet and velocity field distributions can be varied in the spray that is formed at the entrance of the combustion chamber. The resulting spray and the flame are characterized using OH-Planar Laser Induced Fluorescence, High Speed Particle Image Velocimetry and Phase Doppler Anemometry measurements. Three staging values, corresponding to three different flame stabilization processes, are analyzed, while power is kept constant. It is shown that mean values are strongly influenced by the fuel distribution and the flame position. Using adequate post-processing, the interaction between the acoustic field and the droplet behavior is characterized. Spectral analysis reveals a strong acoustic-flame coupling leading to a low frequency oscillation of both the velocity field and the spray droplet distribution. In addition, acoustic measurements in the feeding line show that a strong oscillation of the acoustic field leading to a change in fuel injection, and hence droplet behavior.

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