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In this work we present the numerical simulation of air-assisted liquid atomization at high pressure using the Smoothed Particle Hydrodynamics (SPH) method. Different post-processing tools are applied to facilitate the comparison with experimental observations. This allows to quantitatively validate the numerical method against the experiment, in terms of (i) frequency of the Kelvin-Helmholtz instability that develops on the jet surface, and (ii) statistical distribution of the jet intact length. The qualitative comparison also shows a good prediction of the jet global instability and of the fragmented liquid lumps, with regards to length and time scales. In addition, the post-processing tools also give access to the local parameters of the generated spray in the vicinity of the nozzle, which are not easily accessible in a real experiments. Using these tools, 1D profiles and 2D maps of the liquid phase properties such as the volume fraction, the droplet concentration, the Sauter Mean Diameter (SMD) and the droplet sphericity are presented. Because of the Lagrangian nature of the SPH method, it is also possible to monitor the whole atomization cascade as a causal tree, from the primary instabilities to the spray characteristics. This tree contains various information such as the fragmentation spectrum and the breakup activity, which are of great interest for researchers and engineers. Hence, the capability of the Smoothed Particle Hydrodynamics (SPH) method for simulating air-assisted atomization at high ambient pressure is demonstrated as well as its applicability to realistic configurations. This is a first step towards the development of a complete virtual spray test-rig.

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A twin-fluid atomizer configuration is predicted by means of the 2D weakly-compressible Smooth Particle Hydrodynamics (SPH) method and compared to experiments. The setup consists of an axial liquid jet fragmented by a co-flowing high-speed air stream (U g ≈ 60 m/s) in a pressurized atmosphere up to 11 bar (abs.). Two types of liquid are investigated: a viscous Newtonian liquid (µ l = 200 mPa s) obtained with a glycerol/water mixture and a viscous non-Newtonian liquid (µ l,apparent. ≈ 150 mPa s) obtained with a carboxymethyl cellulose (CMC) solution. 3D effects are taken into account in the 2D code by introducing (i) a surface tension term, (ii) a cylindrical viscosity operator and (iii) a modified velocity accounting for the divergence of the volume in the radial direction. The numerical results at high pressure show a good qualitative agreement with experiment, i.e. a correct transition of the atomization regimes with regard to the pressure, and similar dynamics and length scales of the generated ligaments. The predicted frequency of the Kelvin-Helmholtz instability needs a correction factor of 2 to be globally well recovered with the Newtonian liquid. The simulation of the non-Newtonian liquid at high pressure shows a similar breakup regime with finer droplets compared to Newtonian liquids while the simulation at atmospheric pressure shows an apparent viscosity similar to the experiment. NOMENCLATURE *