Nonlinear simulation of free surfaces and atomization in pressure swirl atomizers

Abstract

A fully nonlinear boundary element method (BEM) model has been developed to simulate the pressure swirl or simplex atomizer. The free surface inside the vortex chamber and within the hollow-cone/primary atomization zone is simulated with a fourth order scheme thereby permitting investigation of highly distorted surfaces up to the point where atomization occurs. For the axisymmetric calculations, annular rings of fluid are pinched from the main liquid domain. Swirling flow is simulated via a superposition of a potential vortex with the base axial flow emanating from the nozzle in a BEM formulation. Results show good comparison to film thicknesses from test data as well as from linear one-dimensional theory. Parametric studies are conducted to assess the influence of injector geometry and flow characteristics on film thickness and spray angle produced by the atomizer. Limited results are also provided to compare droplet sizes with experimental data. In this regard, the linear stability analysis of Ponstein is used to predict the number of droplets created from each ring of fluid shed by the axisymmetric calculation.