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Eulerian modeling and simulation of polydisperse moderately dense coalescing spray flows with nanometric-to-inertial droplets : application to Solid Rocket Motors

Abstract : In solid rocket motors, the internal flow depends strongly on the alumina droplets, which have a high mass fraction. The droplet size distribution, which is wide and spreads up with coalescence, plays a key role. Solving for unsteady polydisperse two- phase flows with high accuracy on the droplet sizes is a challenge for both modeling and scientific computing: (1) very small droplets, e.g. resulting from the combustion of nanoparticles of aluminum fuel, encounter Brownian motion and coalescence, (2) small droplets have their velocity conditioned by size so they coalesce when having different sizes, (3) bigger droplets have an inertial behavior and may cross each other’s trajectory, and (4) all droplets interact in a two-way coupled manner with the carrier phase. As an alternative to Lagrangian approaches, some Eulerian models can describe the disperse phase at a moderate cost, with an easy coupling to the carrier phase and with massively parallel codes: they are well-suited for industrial computations. The Multi- Fluid model allows the detailed description of polydispersity, size/velocity correlations and coalescence by separately solving “fluids” of size-sorted droplets, the so-called sections. In the present work, we assess an ensemble of models and we develop a numerical strategy to perform industrial computations of solid rocket motor flows. (1) The physics of nanoparticles is assessed and included in a polydisperse coalescing model. High order moment methods are then developed: (2) a Two-Size moment method is ex- tended to coalescence to treat accurately the physics of polydispersity and coalescence and the related numerical developments allow to perform applicative computations in the industrial code CEDRE; (3) a second order velocity moment method is developed, together with a second order transport scheme, to evaluate a strategy for a moderately inertial disperse phase, and academic validations are performed on complex flow fields; (4) a time integration strategy is developed and implemented in CEDRE to treat efficiently two-way coupling, in unsteady polydisperse cases including very small particles. The developments are carefully validated, either through purposely derived analytical formulae (for coalescence and two-way acoustic coupling), through numerical cross-comparisons (for coalescence with a Point-Particle DNS, for applicative cases featuring coalescence and two-way coupling with a Lagrangian method), or through available experimental results (for coalescence with an academic experiment, for the overall physics with a sub-scale motor firing). The whole strategy allows to perform applicative computations in a cost effective way. In particular, a solid rocket motor with nanoparticles is computed as a feasibility case and to guide the research effort on motors with nanoparticle fuel propellants.
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https://tel.archives-ouvertes.fr/tel-01009896
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  • HAL Id : tel-01009896, version 2

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François Doisneau. Eulerian modeling and simulation of polydisperse moderately dense coalescing spray flows with nanometric-to-inertial droplets : application to Solid Rocket Motors. Other. Ecole Centrale Paris, 2013. English. ⟨NNT : 2013ECAP0030⟩. ⟨tel-01009896v2⟩

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