Dispensing Liquids with Swirl Spray Nozzles

Swirl-spray nozzles are a common way to dispense liquids in chemical cleaners, medicines and fuels. For successful atomization of the liquid, it is usually necessary to form an air core that penetrates into the nozzle. CFD is an effective way to explore the influence of geometry, swirl velocity, and fluid properties for an optimum spray cone.

Swirl spray nozzles
FLOW-3D simulation of a swirl spray nozzle

In this example, a two-dimensional axisymmetric swirl flow has been simulated. An air core along the axis of symmetry has nearly penetrated up the entire length of the nozzle. The left plot is a pressure distribution with the vectors representing a velocity distribution in the plane. The right plot is colored by the swirl component of velocity with red indicating the higher values.

It is not possible to directly compute the complete atomizations of a spray because the scales of the spray cone and droplet sizes are too broad. Also, atomization is a chaotic process closely tied to external perturbations, microscopic imperfections in a nozzle and other influences. However, being able to predict the properties of a spray cone as it leaves the nozzle (i.e., wall thickness, cone angle, axial and azimuthal velocities) goes a long way toward optimizing this type of flow device.