Learning Forum

[jazi1212]

Hello,

 

I am using Multiphase euler model along with Population balance model for my case. In my case there is no backflow but when i define pressure outlet boundary conditions, it asks me for a backflow volume fraction and also asks for turbulence case to be defined in terms of intensity and dissipation rate.

 

What are the values i should put or options i should consider to make the case understood that there is no backflow of any case.

[Rob]

They're needed incase flow enters the domain from the outlet. It's probably OK to set the back flow as primary phase only and turbulence based on the boundary size etc: how did you set it for the inlet?

[jazi1212]

i have a velocity inlet so i put volume fraction for droplets 1 and provided separate velocities for inlet of air and droplets. However i know for a fact that there will be no backflow in my case. I think i read it somewhere that even if no backflow is expected still set realistic values of backflows at the outlet.

[DrAmine]

Backflow quantities are required whenever therer will be a numerical recirculation happening or a physical re-entrainment from outside.

Example: bubble rising in a tank filled with half air half water and the top boundary is atmospheric pressure boundary.

[jazi1212]

air as primary flow

water droplets as secondary flow

case is horizontal annular pipe

eulerian multiphase model

for pressure outlet, what do you suggest either i take volume fraction of air=1 or droplets=1?

In real scenario, i know that there is no backflow of air in my case. droplets wont be coming back from outlet but maybe droplets circulate and fall down on lower wall of pipe.

[Rob]

If there are no droplets coming back in then setting air as vol frac of 1 makes sense.  It's entirely down to the model so we can't really advise without all of the information.  Run the model and see what happens.