A. Sänger

SPH Simulation of a Twin-Fluid Atomizer Operating with a High Viscosity Liquid

G. Chaussonnet, S. Braun, L. Wieth, R. Koch, H.-J. Bauer A. Sänger, T. Jakobs, N. Djordjevic, T. Kolb Karlsruher Institut für Technologie (KIT), Karlsruhe, Germany 1Institute of Thermal Turbomachines, KIT Campus South 2Institute of Technical Chemistry, KIT Campus North 3Engler-Bunte-Institute, KIT Campus South *geoffroy.chaussonnet@kit.edu Abstract A Smooth Particles Hydrodynamics (SPH) 2D simulation of a twin-fluid atomizer is presented and compared with experiments in the context of bio-fuel production. The configuration consists in an axial high viscosity liquid jet (μl ≈ 0.5 Pa.s) atomized by a coflowing high-speed air stream (ug ≈ 100 m/s) at atmospheric conditions, and the experiment shows two types of jet instability (flapping or pulsating) depending on operating conditions and the nozzle geometry. In order to capture the 3D effects of the axial geometry with a 2D simulation, the surface tension force and the viscosity operator are modified. The mean and RMS velocity profiles of the single phase simulations show a good agreement with the experiment. For multiphase simulations, despite a qualitative good agreement, the type of instabilities as well as its frequency are rarely well captured, highlighting the limitation of 2D geometry in the prediction of 3D configurations.

SPH Simulation of an Air-Assisted Atomizer Operating at High Pressure: Influence of Non-Newtonian Effects

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 (Ug ~ 60 m/s) in a pressurized atmosphere up to 11 bar (abs.). Two types of liquid are investigated: a viscous Newtonian liquid (µ = 200 mPa.s) obtained with a glycerol/water mixture and a viscous non-Newtonian liquid (µ ~ 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.