An introduction to vortex flows and their implications on solid-liquid separation
There is often ambiguity in what constitutes vortex behaviour, and common descriptions are qualitative in nature and therefore necessarily limited. It has become common to identify quantitative features associated with vortices in order to provide a definition.
Theoretical vortex behaviours provide a foundation of understanding, and it is helpful to examine the vortex core region to illustrate dominant features. Two theoretical behaviours exist: free and forced motion. In a real fluid, however, neither the forced nor the free vortex behaviours prevail—meaning that theoretical behaviours are of limited practical application.
In real fluids some blending between the forced and free vortex behaviours is always observed, though in the vast majority of real-world industrial flows there is a strong tendency to exhibit free vortex behaviour, whereas the dominance of forced vortex behaviour is only observed in the vortex core and in lower Reynolds number flows.
A full understanding of real-world vortex behaviour enables engineers to develop hydrodynamic separators that minimise short circuiting and maximise the residence time of the fluid, ensuring that the best use is made of the available volumes. With this understanding, separation units can be designed to be resistant to changes in inflow conditions, enabling them to collect a wide range of materials across a wide range of flow rates.