C. Habchi, B. M. Devassy, R. Kumar, N. Gillet, A.Velghe, J. Bohbot LES of in-nozzle flows and liquid jet atomization using a two-surfaces density model C. Habchi, B. M. Devassy, R. Kumar, N. Gillet, A.Velghe, J. Bohbot LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

The CFD Grand Challenge (1) Without String Cavitation With String Cavitation Experimental images taken from : A. Andriotis and M. Gavaises Atomization and Sprays, 19(3):247–261, 2009 LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

The CFD Grand Challenge (2) Computing Cavitation and Atomization What are the main ingredients to compute cavitation and liquid jet atomization ? LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

Outline Two-phase flow, Cavitation and Atomization models description Application of these models to the understanding of in-nozzle flows in Marine Diesel injectors Summary and Future work LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

The two-fluid model A generalized turbulent multi-species formulation of the highly compressible two-fluid 7-Equations model. LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

The Gibbs Energy Relaxation Model (GERM) Relaxation procedures for interfacial terms The velocity, pressure and temperature interfacial terms are modeled using quasi-instantaneous relaxation procedures toward equilibrium: Procedures for SV and SP , see : Saurel R. & Abgrall R. (1999), JCP,150, 425-467 Saurel R. et al. (2008) JFM, 607, 313-350 Procedures for ST and Sg , see : Zein A. et al. (2010), JCP, 229, 2964-2998 Habchi C. (2014), AAS LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

Main features of the GERM cavitation model(*) GERM cavitation model does not use adjustable constants GERM model can predicts two cavitation regimes: Gaseous cavitation regime The gaseous cavitation regime : it appears in region in which the static pressure is close to but above the liquid saturation pressure Vaporous cavitation regime The vaporous cavitation regime : it may happen when the static pressure goes below the liquid saturation pressure. * C. Habchi , Atomization and Sprays , DOI:10.1615/AtomizSpr.2014010372, 2014. LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

Closures of the two-fluid model Equations of state (EOS) Multi-species gas phase are closed by the perfect gas EOS: Single-species liquid phase is closed by the Stiffened Gas SG-EOS: For liquid n-dodecane: g LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

SGS Turbulence Model for the Two-Phase System Smagorinsky model l= (liquid or gas) 0.2 Sij is the rate of strain tensor and D is the local cell size LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

Scenario for the modeling of primary atomization Second image First image Exp observation of ligament breakup by Marmottant & Villermaux (2004) Liquid Gas ligaments Liquid Gas droplets Liquid Gas Control Volume Ligaments are assumed to be formed due to the stretching of the interface mainly by the fluctuating rate of strain normal to the interface. LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

The Two Surface Density (TwoSD) Atomization Model Surface density definitions Sd Ss Liquid core (index s) LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

The TwoSD atomization model* Primary atomization of the liquid core (index s) Interface Stretching Primary atomization Relaxation of P,T,g Secondary breakup of the droplets (index d) + Droplets breakup, coalescance * B. M. Devassy, C. Habchi, E. Daniel, Atomization and Sprays, DOI: 10.1615/AtomizSpr.2014011350, vol. 25, 2014. LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

Two-phase flow (TPF) numerical solver* IFP-C3D start Red arrows for TPF solver TwoSD Atomization&breakup model Lagrangian Atomization model Liquid phase Solver Time: 1st order Space: quasi-2nd order Single gas phase Solver Time: 1st order Space: quasi-2nd order Stiff relaxation procedures for interfacial terms: GERM cavitation model End * J. Bohbot et al., Oil & Gas Science and Technology, vol. 64, 2009 LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

Numerical investigation of in-nozzle flows in large marine Diesel injectors Fuel inlet 3 Million cells Discharge pipe Spray Combustion Chamber Injection hole Cells size = 25 microns LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

Numerical investigation of nozzle orifices eccentricity Simulations have been carried out : Simulation 1 : hole eccentricity (e=0) Simulation 2 : hole eccentricity (e=0.8) Cross-section A-A through the injection orifice (middle). Cross-section B-B through the injector bore (right) LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

Initial & boundary conditions Pinj = 700 bar Initial velocity = 0 m/s Pgas = 40 bar LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

Non-eccentric nozzle(cross-section B-B): Liquid volume fraction Cavitation leads to: A reduced flow rate (Cd decreases down to around 0.6) A deviated liquid jet (which corroborates the experiments) LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

Eccentric nozzle (cross-section B-B): Liquid volume fraction The cavitation pocket is smaller than for e=0 No liquid jet deviation (which corroborates the experiments) LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

Eccentric nozzle (cross-section A-A): Liquid volume fraction A liquid jet deviation is obtained (which corroborates the experiments) LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

Eccentric nozzle : Liquid core and velocity field al=0.5 Cavitation Liquid core deviation The fluid circumvents the cavitation pocket in the hole The liquid is clearly deviated from the hole axis LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

Eccentric nozzle (cross-section B-B): Spray droplets diameter The smallest droplets (around 1 micron) are atomized at the cavitation pocket side. LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

Conclusion In this study, simultaneous simulations of the in-nozzle cavitation and of the atomization of the liquid jet have been carried out. In this aim, the GERM cavitation model and the TwoSD atomization model, recently developed have been used. The impacts of the cavitation on the liquid spray characteristics of large marine injectors have been highlighted. Particularly, it has been shown that cavitation is at the origin of the spray deviation observed experimentally. The smallest droplets are atomized at the cavitation pocket side. LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

Future work will focus on quantitative validation of the GERM and TwoSD models. In addition, more accurate numerical schemes will be investigated in the context of the LES simulations of two-phase highly compressible flows. LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France

LES4ICE, 4-5 Dec. 2014, Rueil-Malmaison - France