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Von Karman Institute

 Numerical simulations of Focus sprays have been performed at the von Karman Institute for Fluid Dynamics (www.vki.ac.be) with CFD (Computational Fluid Dynamics) software ANSYS version 12.1. The computational domain has been meshed by Gambit with about 2 million hexahedral cells. 

 The flow motion is described by the equations of mass and momentum conservation (incompressible Navier-Stokes equations). Two extra transport equations have been introduced to represent the turbulent properties of the flow with a standard k-e turbulence model. Standard wall functions have been used at the ground wall. A uniform velocity profile has been applied as a boundary condition when wind is taken into account.

 The droplet motion at the outlet of the spray is simulated with a Lagrangian approach, i.e. solving the equation of motion for each particle, taking the effect of the air flow into account. Velocity and diameter of the droplets forming the spray must be imposed as a boundary condition. These conditions are obtained from the experimental data acquired by the von Karman Institute using Phase Doppler Interferometry (PDI).

 After numerically solving the motion equations, a file containing the set of positions occupied by the droplets is exported for obtaining the spray envelops.

An in-house developed script examines the exported data file and determines the path followed by the droplets ejected through the nozzle. Finally, the identified paths are converted into lines and saved in as a CAD file.

The results of numerical simulations have been validated with measurements acquired in full-size experiments, where the form and the dimensions of the spray envelop have been quantified.