Aspects of Combustion Stability in Liquid Propellant Rocket Motors Part I: Fundamentals. Low Frequency Instability With Monopropellants

Crocco, L.

doi:10.2514/8.4393

Cited by 265 publications

(94 citation statements)

References 2 publications

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“…Such models describe the combustor as a network of connected modules, and exploit the fact that one of the two phenomena key to the combustion instability mechanism, the acoustic waves, are very well modelled using simple analytical approaches. The response of the flame unsteady heat release rate to perturbations can be captured via a flame model [8,9]. The flame model should incorporate non-linearity at higher amplitudes, with this now established as being the main mechanism responsible for saturation into limit cycle in gas turbine combustors.…”

Section: Introductionmentioning

confidence: 99%

Simulation of the flame describing function of a turbulent premixed flame using an open-source LES solver

Han

Morgans

2015

Combustion and Flame

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Numerical simulations were used to characterise the non-linear response of a turbulent premixed flame to acoustic velocity fluctuations. The test flame simulated was the bluff body stabilised flame which has been the subject of a detailed experimental study (Balachandran et al., 2005, Combustion & Flame). Simulations were performed using Large Eddy Simulation (LES) via the open source Computational Fluid Dynamics (CFD) software, Code S aturne, with combustion modelled by combining a Flame Surface Density (FSD) method with a fractal approach for the wrinkling factor. The cold flow field and the unforced reacting flow were used for preliminary code validation. In order to characterise the non-linear response of the unsteady heat release rate to acoustic forcing, a harmonically varying velocity fluctuation, for which both the forcing frequency and normalised forcing amplitude were varied, was imposed. The flame response was characterised via a Flame Describing Function (FDF), also known as a nonlinear flame transfer function, for which the gain and phase shift depend on forcing amplitude as well as forcing frequency. The response at four frequencies was compared to experimental data in detail, confirming that the LES results captured both the qualitative flame dynamics and the quantitative response of the heat release rate with very reasonable accuracy. The full FDF was then obtained across more frequencies, again showing a good fit with the experimental data, other than for a slight under-prediction in gain, most probably due to neglecting the effect of wall heat loss and the effect of combustion modelling. The agreement was significantly better than has been obtained previously for this test case using numerical simulations. Finally, it was found that increasing combustor length had little affect on the flame response, which may prove useful for future long combustor stability and limit cycle analysis. This work thus confirms that LES, in this case via the open source Code S aturne, provides a useful tool for characterising the response of lean premixed turbulent flames.

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Section: Introductionmentioning

confidence: 99%

Simulation of the flame describing function of a turbulent premixed flame using an open-source LES solver

Han

Morgans

2015

Combustion and Flame

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“…They are due to a resonant coupling of the unsteady heat release and the acoustics propagating in the system and their prediction has become an important task to prevent their appearance at an early design stage [18][19][20]. For acoustically compact flames the linear analysis of combustion instabilities is generally performed with the Flame Transfer Function (FTF) introduced by Crocco [21,22] and more recently with the Flame Describing Function (FDF) [23,24]. In these approaches the FTF is defined as the relative heat release fluctuation ðq=qÞ to the relative inlet velocity perturbation ðû=uÞ induced by the acoustic field:…”

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confidence: 99%

Bistable swirled flames and influence on flame transfer functions

Hermeth

Staffelbach

Gicquel

et al. 2014

Combustion and Flame

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Large Eddy Simulations (LES) are used to study a lean swirl-stabilized gas turbine burner where the flow exhibits two stable states. In the first one, the flame is attached to the central bluff body upstream of the central recirculation zone which contains burnt gases. In the second one the flame is detached from the central bluff body downecirculation zone which is filled by cold unburnt gases and dominated by a strong Precessing Vortex Core (PVC). The existence of these two states has an important effect on the dynamic response of the flame (FTF): both gain and phase of the FTF change significantly in the detached case compared to the attached one, suggesting that the stability of the machine to thermoacoustic oscillations will differ, depending on the flame state. Bifurcation diagrams show that the detached flame cannot be brought back to an attached position with an increased fuel flow rate, but it can be re-attached by forcing it at high amplitudes. The attached flame however, behaves inversely: it can be brought back to the detached position by both decreasing or increasing the pilot mass flow rate, but it remains attached at all forcing amplitudes. IntroductionSwirling flows are commonly used to help flame stabilization in gas turbine combustion chambers. They feature several types of vortex breakdown and can exhibit bifurcation phenomena where different states can co-exist and the flow can jump spontaneously from one to another [1,2]. Bifurcations of flames in configurations which are close to real gas turbine chambers have not been investigated so far even though engineers report that they observe these mechanisms and that there is a link between flame states and thermoacoustic instabilities: when the flame changes from one state to another, its acoustic stability characteristics also change.Two dynamic phenomena are usually observed in swirled combustion chambers: (1) a helical flow instability, the so-called precessing vortex core (PVC) and (2) thermo-acoustic instabilites.The PVC is an hydrodynamic instability in swirling flows [3].I t is a large scale structure characterized by a regular rotation of a spiral structure around the geometrical axis of the combustion chamber. It can occur at high Reynolds and swirl number flows [4][5][6][7][8][9][10] and its precession frequency is controlled by the rotation rate of the swirled flow [3]. Several studies show that combustion can suppress the PVC [6,7,11], but other cases also show PVCs which are present in reacting flows [12][13][14][15]. The interaction of PVC with flames has been analyzed for example by Stöhr et al.[16]: they found the PVC to enhance mixing and to increase the flame surface. This was associated to structures in the inner shear layer, whereas Moeck et al. [15] observed the outer shear layer to create most of the flame perturbations. Both researchers as well as Staffelbach [13] using LES evidenced a ''finger-like'' rotating structure at the flame foot around which the PVC is turning. Furthermore, asymmetric fluctuations of the he...

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“…Numerically, the study and prediction of annular chamber stability can be achieved by using one dimensional networks [1,6] or Helmholtz solvers [7,8]. These methods rely on the concept of the flame transfer function [9], which remains a key element and needs to be evaluated, using Large Eddy Simulation (LES) for example, or modeled [4,9,10]. Although LES could potentially predict combustion instabilities, until recently its use was restrained to the modeling of the flame transfer function obtained on a single sector simulation.…”

Section: Introductionmentioning

confidence: 99%

Massively parallel LES of azimuthal thermo-acoustic instabilities in annular gas turbines

Wolf

Staffelbach

Gicquel

et al. 2009

J. Phys.: Conf. Ser.

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Massively parallel LES of azimuthal thermo-acoustic instabilities in annular gas turbines Abstract. Most of the energy produced worldwide comes from the combustion of fossil fuels. In the context of global climate changes and dramatically decreasing resources, there is a critical need for optimizing the process of burning, especially in the field of gas turbines. Unfortunately, new designs for efficient combustion are prone to destructive thermo-acoustic instabilities. Large Eddy Simulation (LES) is a promising tool to predict turbulent reacting flows in complex industrial configurations and explore the mechanisms triggering the coupling between acoustics and combustion. In the particular field of annular combustion chambers, these instabilities usually take the form of azimuthal modes. To predict these modes, one must compute the full combustion chamber comprising all sectors, which remained out of reach until very recently and the development of massively parallel computers. A fully compressible, multi-species reactive Navier-Stokes solver is used on up to 4096 BlueGene/P CPUs for two designs of a full annular helicopter chamber. Results show evidence of self-established azimuthal modes for the two cases but with different energy containing limit-cycles. Mesh dependency is checked with grids comprising 38 and 93 million tetrahedra. The fact that the two grid predictions yield similar flow topologies and limit-cycles enforces the ability of LES to discriminate design changes.

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Aspects of Combustion Stability in Liquid Propellant Rocket Motors Part I: Fundamentals. Low Frequency Instability With Monopropellants

Cited by 265 publications

References 2 publications

Simulation of the flame describing function of a turbulent premixed flame using an open-source LES solver

Simulation of the flame describing function of a turbulent premixed flame using an open-source LES solver

Bistable swirled flames and influence on flame transfer functions

Massively parallel LES of azimuthal thermo-acoustic instabilities in annular gas turbines

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