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Numerical modelisation of a premixed flame’s burned gases jet instability under an acceleration effects

Abstract : Oscillatory phenomena's study in premixed flames has led to many investigations that have made us able to draw a conclusion for the dependence of the flickering (pumping phenomenon) of the flame tip on the downward acceleration field g. The power dependence of the pumping frequency on g of the form 2 1 g   has been experimentally revealed 1,2. These experimental results have found a theoretical verification 3,4 but there are some unknowns left and that states the reason of our investigations by direct numerical investigations (DNS). The thermochemical aspect of the problem is reproduced as boundary conditions on the flame front by giving the latter's profile and the velocity and temperature fields on this profile. These depend on the reaction energy, on reaction rates and on transfer coefficients-what leads to the laminar adiabatic flame combustion velocity value-on fresh gases velocity an on the local stretch at the flame tip. The hydrodynamic problem is thus uncoupled to the chemical one and then we make the direct simulation of Navier-Stokes equations by using the software "flame" 5-made in collaboration with Francis Dupoirieux of ONERA-at first for the calculations relating to the entirely conical flame configuration, then for the calculations relating to a partially conical configuration with a parabolic profile of the flame tip. We have done calculations of different values of the acceleration field intensity, to carry out its dependence law with the oscillation's frequency in the burned gaze's jet. Experimental results obtained with normal gravity g0 (i.e. V=9,81 m/s 2) give a value of the characteristic frequency fc in the order of 16-17 Hz [ref. 1] whilst we obtain 25.8 Hz with the conical flame model and around 20 Hz with the parabolic flame tip model. We use the conical model for the variation of g between g=0 to g=10g0 and find a presupposed frequency law in 0 g g with a proportionality coefficient equal to 16.9, that is a satisfactory result. The dispersion of our results and the behavior around g=0-we find a frequency of 8.4 Hz instead of zero-nevertheless show the insufficiencies of the models. In prospect, we envisage to use the parabolic flame tip model for the variation of the acceleration field intensity, write less rigid boundary conditions on the flame front so as to obtain flame profile oscillations, study the influence of obstacles placed in the flow and quantified the Reynolds Number effects. 1 D. Durox, F. Baillot, P. Scouflaire & R. Prud’homme "Some effects of gravity on the behaviour of premixed flames" Combustion and Flame, 82, 1990, pp. 66-74. 2 L. W. Kostiuk and R.K. Cheng, 1995. " The coupling of conical wrinkled laminar flames" Combustion and Flame, 103, pp. 27-40. 3 R. Prud'homme, 1992. "Flammes de prémélange air-méthane en microgravité : éléments théoriques" Ann. Chim. Fr., 17, 1992, pp. 13-26. 4 A.A. Konov, August 1993. "Effect of gravity on conical flame oscillations", 14th inter. Col. On Dynamics of Explosions and Reactive Systems, Univ. of Cambria, Portugal 5 J. Roy, 1995. "Mise au point d'un code de calcul pour l'étude des instabilités hydrodynamiques dans les flammes de prémélange", thèse de l'Université Pierre et Marie Curie
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Submitted on : Monday, July 8, 2019 - 2:12:58 AM
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  • HAL Id : hal-02176231, version 1


Moussa Samba, Roger Prud'Homme, Louis Gottesdiener. Numerical modelisation of a premixed flame’s burned gases jet instability under an acceleration effects. Biennial Meeting of European Low Gravity Research Association (ELGRA), Paris, 17-19 mars 1997., Mar 1997, Paris, France. ⟨hal-02176231⟩



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