PhD defense - P. Sierra Sanchez

Modelling the dispersion and evaporation of sprays in aeronautical combustion chambers

Delivered by Institut Nationale Polytechnique de Toulouse
Speciality: Energetic and transfer

January 23, 2012 - CERFACS

Combustion still represents about 90% of the energy production in the world. Most industrial burners are fuelled with liquid hydrocarbons. However, most studies have been dedicated to gaseous ?ames and the impact of liquid spray is still misunderstood. The purpose of this study is to improve the modelisation of two main phenomena occurring between atomization and combustion, i.e. the droplet dispersion in the turbulent gaseous flow and the evaporation process, in the context of Large Eddy Simulation (LES) of complex configurations. First, the mesoscopic Euler-Euler approach (Février et al., 2005) based on a conditioned ensemble averaging and implemented in AVBP is improved. The closure model (Simonin, 2001, Kaufmann, 2004) for the second-order moments appearing in the transport equations solved fails in mean-sheared configurations (Riber, 2007). Several new models proposed by Masi, 2010 and a priori tested in a particle-laden slab are tested a posteriori in the same configuration. A quantitative analysis based on several calculations varying the Stokes number, the gaseous Reynolds number and the grid resolution allows to retain a non-linear model using the particle rate-of-strain tensor as timescale and called 2FEASM3. The second part consists in improving the evaporation model implemented in AVBP which assumes infinite conduction in the liquid and spherical symmetry in the gas phase along with simplified thermodynamics and transport properties calculation. A new model is proposed, where the dependence of gaseous mixture viscosity on local composition is accounted for, and the Prandtl and Schmidt numbers are fixed by a reference equilibrium calculation using complex thermodynamics and transport properties. This method shows good agreement with experimental measurements in the configuration of an isolated droplet evaporating in quiescent N2 without further increasing the computational cost. Finally, the impact of the new models is analysed in the LES of the MERCATO semi-industrial configuration (Garcia-Rosa, 2007). Although the experimental data are not sufficient to confirm the results, both the droplet distribution and the fuel mass fraction are significantly affected, which would eventually affect the ignition process.

R.O. Fox	University of Iowa	Referee
J. Réveillon	University of Rouen	Referee
O. Simonin	INP Toulouse	Member
S. Jay	IFPEN, Rueil Malmaison	Member
A. Roux	Turbomeca, Bordes	Member
L. Gicquel	CERFACS	Advisor

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