Evaluation of a Multifluid Mesoscopic Eulerian Formalism on the Large Eddy Simulation of an aeronautical-type configuration
Résumé
This work describes the evaluation of a fully eulerian method to simulate polydisperse turbulent two phase flows: the Multifluid Mesoscopic Eulerian Formalism (MMEF). This approach is derived from the coupling between the Mesoscopic Eulerian Formalism (MEF) of Février et al. (2005), and the Multifluid Approach (MA) of Laurent and Massot (2001). The MA handles polydispersion by using a discretization of the droplet size space, whereas the MEF describes the velocity dispersion of monodisperse turbulent particle flows. The coupling of the two methods is expected to capture both behaviors. A first step toward this kind of approach was initially studied in Massot (2007), and the differences with the present work lie in the closure and modelling assumptions. MMEF is integrated into the AVBP code from CERFACS/IFP, which solves the compressible Navier-Stokes equations for reactive flows with low dissipation schemes adapted to Large Eddy Simulation. These schemes encounter some difficulty for the Eulerian description of the liquid dispersed spray, highly compressible and showing stiff gradients and vacuum areas of droplet density. Specific numerical procedures are used to stabilize locally the solution, with limited effect on the accuracy. The model is applied to the MERCATO aeronautical-type configuration. An analysis of characteristic time scales allows to evaluate the importance of polydispersion in this test rig. A preliminary test case consists in the evaporation of a chosen distribution in one computational cell. Physical conditions are the same as in MERCATO. Results are compared to the evaporation strategy used with MEF, and show the necessity to account for polydispersion description in order to capture size-velocity correlations. A second test case is a two-dimensional vortex entraining droplets, in which droplets are injected uniformly. Due to the polydispersion of the liquid and its resulting centrifugal force, a spatial distribution of droplet mean diameter is observed, and confirms again the necessity of polydispersion. Finally, the MMEF is applied to the MERCATO test rig, for which both experimental and numerical data are available. Comparisons of velocity profiles at selected downstream positions show a good agreement with measurements of MEF and MMEF in the central zone, whereas only the MMEF is able to capture the external zone. Comparisons of Droplet Number Density function at selected volumes inside the chamber also show a good agreement between MMEF and experiments.