back flow level set function flux, what is it?
 

While, I was trying to setup VOF model with 'Couple Set + VOF' parameter options, I came across this
'' Back flow level set function flux '' option, in boundary conditions for 'pressure-outlet' condition. It was under multiphase sub-option, and version of software is 17.0.
And my inlet conditions are, 'mass-flow-rate'.
Since I'm setting up pipe flow the turbulence conditions are, 'turbulence intensity and hydraulic diameter'. The values are 30% and inlet diameter of geometry.
So I just wanna know, what's this, 'back flow level set function flux'?
I tried to understand by reading math journal papers, but there is no difference in aerodynamic turbulent flow over sphere and knowledge over my head!!

thanks, regards.