The effect of nozzle internal flow on spray atomization

The effect of nozzle surface features on the overall atomization behavior of a liquid jet is analyzed in the present computational work by adopting three representative geometries, namely a single X-ray tomography scan of the Engine Combustion Network’s Spray A nozzle (Unprocessed), a spline reconstruction of multiple scans (Educated), and a purely external flow configuration. The latter configuration is often used in fundamental jet atomization studies. Numerically, the two-phase flow is solved based on algebraic volume-of-fluid methodology utilizing the OpenFoam solver, interFoam. Quantitative characterization of the surface features concerning the first two geometries reveals that while both of them have similar levels of cylindrical asymmetries, the nozzle configuration pertaining to the Unprocessed geometry has much larger surface features along the streamwise direction than the Educated geometry. This produces for the Unprocessed configuration a much larger degree of non-axial velocity components in the flow exiting the orifice and also a more pronounced disturbance of the liquid surface in the first few diameters downstream of the nozzle orifice. Furthermore, this heightened level of surface destabilization generates a much shorter intact liquid core length, that is, it produces faster primary atomization. The surprising aspect of this finding is that the differences between the Unprocessed and Educated geometries are of O (1) μm, and they are able to produce O (1) mm effects in the intact liquid core length. In spite of more pronounced atomization for the Unprocessed geometry, the magnitude of the turbulent liquid kinetic energy is roughly the same as the Educated geometry. This highlights the important role of mean field quantities, in particular, non-axial velocity components, in precipitating primary atomization. At the other end of the spectrum, the external-only configuration has the mildest level of surface disturbances in the near field resulting in the longest intact liquid core length.