Actual Impedance of Nonreflecting Boundary Conditions:  Implications for Computation of Resonators

Selle, Laurent; Nicoud, Franck; Poinsot, Thiérry

doi:10.2514/1.1883

Cited by 141 publications

(99 citation statements)

References 32 publications

(38 reference statements)

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“…A basic proof of the absence of acoustic coupling can be assessed by comparing the acoustic eigenfrequencies of the combustion chamber with the precessing frequency of the PVC (408 Hz). The fundamental transverse eigenmode is 575 Hz, and the non reflecting inlet/outlet treatment [24] is built to damp all the longitudinal modes.…”

Section: Resultsmentioning

confidence: 99%

“…The boundary condition treatment is based on a multi-species extension [19] of the NSCBC method [23], for which the acoustic impedance is controlled to minimise the unwanted reflections [24]. The adiabatic walls are handled using a logarithmic lawof-the-wall formulation which is known to perform well with the classical Smagorinsky model [25].…”

Section: Numerical Approach Used In Large Eddy Simulationsmentioning

confidence: 99%

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Large eddy simulation of piloting effects on turbulent swirling flames

Sengissen

Giauque

Staffelbach

et al. 2007

Proceedings of the Combustion Institute

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Pilot flames, created by additional injectors of pure fuel, are often used in turbulent burners to enhance flame stabilisation and reduce combustion instabilities. The exact mechanisms through which these additional rich zones modify the flame anchoring location and the combustion dynamics are often difficult to identify, especially when they include unsteady hydrodynamic motion. This study presents Large Eddy Simulations (LES) of the reacting flow within a large-scale gas turbine burner for two different cases of piloting, where either 2 or 6 percent of the total methane used in the burner is injected through additional pilot flame lines. For each case, LES shows how the pilot fuel injection affects both flame stabilisation and flame stability. The 6 percent case leads to a stable flame and limited hydrodynamic perturbations in the initial flame zone. The 2 percent case is less stable, with a small-lift-off of the flame and a Precessing Vortex Core (PVC) in the cold stabilisation zone. This PVC traps some of the lean cold gases issuing from the pilot passage stream, changes the flame stabilisation point and induces instability.

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Section: Resultsmentioning

confidence: 99%

Section: Numerical Approach Used In Large Eddy Simulationsmentioning

confidence: 99%

Large eddy simulation of piloting effects on turbulent swirling flames

Sengissen

Giauque

Staffelbach

et al. 2007

Proceedings of the Combustion Institute

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“…4). It was also checked that the reflection coefficients R j , that behave like low-pass filters of cut-off frequency f c = K/(4π ) = 32 Hz [32], let the acoustic fluxes of the harmonic forcing leave and not accumulate in the cavity. This method yielded constant amplitude harmonic signals suitable for the computations of the FTFs, represented in Fig.…”

Section: Measurement Of the Ftf In An Intrinsically Unstable Systemmentioning

confidence: 99%

“…The appropriate reflection coefficients for stabilization R j were obtained from the relaxation coefficients K j enforced through Navier-Stokes Characteristics Boundary Conditions at the inlet and outlet 11 [32]. By choosing K 1 = K 2 = 800 s −1 , the associated complex-valued frequency-dependent reflection coefficients (Fig.…”

Section: Measurement Of the Ftf In An Intrinsically Unstable Systemmentioning

confidence: 99%

DNS of Intrinsic ThermoAcoustic modes in laminar premixed flames

Courtine

Selle

Poinsot

2015

Combustion and Flame

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OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. , Emmert et al. 2015 suggest that thermoacoustic modes can appear in combustors with anechoic terminations, which have no acoustic eigenmodes. These modes, called here Intrinsic ThermoAcoustic (ITA), can be predicted with simple theoretical arguments, but have been ignored for a long time. They are reproduced in this paper using Direct Numerical Simulation (DNS) of a laminar premixed Bunsen type flame. DNS results and theory are compared showing very good agreement in terms of both frequency and mode structure. DNS confirms that the frequency of ITA modes does not depend on any acoustic characteristic of the burner. Based on a numerical evaluation of the Flame Transfer Function, stability limits of ITA modes predicted by theory are also recovered in the DNS with reasonable accuracy. Finally, DNS is used to analyze the mechanisms of ITA modes.

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“…The velocity profile obtained during the periodic simulation is set as a constant and non-reflecting boundary condition [13] at the inlet of the domain for the reactive computations. The pressure P ¼ 2 bar is imposed at the outlet of the network corresponding to the pressure of the gas in FCC regenerators.…”

Section: Numerical Simulation Organizationmentioning

confidence: 99%

Multiscale Study of Reactive Dense Fluidized Bed for FCC Regenerator

Moula

Nastoll²,

Simonin³

et al. 2013

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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Re´sume´-É tude multi-e´chelle d'un lit fluidise´dense re´actif de type re´ge´ne´rateur FCC -Ce travail porte sur les e´coulements re´actifs gaz-particules tels que ceux que l'on rencontre dans la combustion du coke pour la re´ge´ne´ration des particules de catalyseurs de FCC. Les e´tudes re´alise´es pour de tels e´coulements montrent qu'en ge´ne´ral le taux de re´action global au cours du temps est mal pre´dit. La raison peut eˆtre lie´e a`la cine´tique chimique utilise´e qui est en ge´ne´ral base´e sur des expe´riences macroscopiques. Le lien entre des releve´s macroscopiques et une cine´tique chimique de re´action he´te´roge`ne locale qui a lieu a`l'interface meˆme entre la surface de la particule et le gaz environnant n'est pas imme´diat. Nous avons utilise´des re´sultats cine´tiques issus d'expe´riences afin d'identifier les proble`mes qui apparaissent lorsque l'on utilise cette meˆme cine´tique pour des e´chelles diffe´rentes. Une analyse multi-e´chelle est donc effectue´e. Nous montrons alors que la fraction volumique de particules a une influence sur le taux de re´action. Par ailleurs, nous montrons la ne´cessite´de de´velopper un mode`le de sous-maille pour le taux de re´action lie´a`la pre´sence de clustering dans les e´coulements gazparticules. Dans les calculs effectue´s couramment, le taux de re´action est calcule´en conside´rant une re´partition homoge`ne des particules a`l'inte´rieur de la maille de calcul. En effet l'analyse microscopique montre que lorsque les particules sont regroupe´es en nuages denses, la fraction massique de dioxyge`ne a`l'inte´rieur de ce nuage est rapidement nulle et donc le dioxyge`ne est en de´faut. La re´action he´te´roge`ne est donc limite´e.Abstract -Multiscale Study of Reactive Dense Fluidized Bed for FCC Regenerator -This study deals with reactive gas particle flows like the coke combustion during the regeneration of FCC particles. In this kind of reactive flow, the global reaction rate is usually bad predicted. In a first approximation, the chemical scheme can be the reason because of the limitation of its modeling. It is usually based on macroscopic experimental results. The link between these macroscopic measurements and a local kinetics of the heterogeneous reaction occuring at the gas-particle interface is not confirmed. Results of kinetics coming from experimental measurements are used and we try to highlight the problems that appear when the same kinetics are used at different scales. In common industrial computations, coarse meshes are used to solve continuity equations. Averaged or filtered Navier-Stokes and species continuity equations have to be solved in which additional correlation terms appear because of non-linear terms in the original equations, including reaction rate correlation. Therefore a multiscale analysis is performed in order to improve the modeling of this terms. This paper, shows that the eulerian formulation of kinetics has to be improved due to the impact Oil & Gas Science and Technology -Rev. IFP Energies nouvelles, Vol. 68 (2013), No. ...

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Actual Impedance of Nonreflecting Boundary Conditions: Implications for Computation of Resonators

Cited by 141 publications

References 32 publications

Large eddy simulation of piloting effects on turbulent swirling flames

Large eddy simulation of piloting effects on turbulent swirling flames

DNS of Intrinsic ThermoAcoustic modes in laminar premixed flames

Multiscale Study of Reactive Dense Fluidized Bed for FCC Regenerator

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