[shivasluzz]

Can someone please explain,

1. Why is there a particle injection option both in the domain and in the boundaries? How do these both options differ?

2. Is it possible to use Eulerian + Eulerian + Particle injection?

3. With Opening boundary conditions, it is required to specify the Volume fraction. Is it only the initial values? How to specify the Volume fraction at the opening boundary condition if it is not known?

Thank you.

[ghorrocks]

1) There is particle injection options in the domain and boundary levels so you can define particles seeded throughout a domain (eg: particles precipitating out) or the boundary (eg: particles entering through a boundary).

2) Yes, I think so. Try it to be sure.

3) You specify the VF at an opening only for Eularian models. Please note that the definition of a boundary condition is a location where you know enough about the flow that you can define the condition there. If you do not know the reverse flow VF then you cannot put a boundary condition there, and you need to move it to somewhere you do know the fluid condition.

[shivasluzz]

Thanks ghorrocks!

Regarding question no. 3:

There are some cases where we don't know the VF before the simulation. For example, I am doing a spray or atomizer simulation, where a liquid from the atomizer is sprayed into the chamber having air. The bottom wall of the chamber always has some air recirculation, since the liquid spray is dragging the air along with it. Because of this anticipated air recirculation, I want to use the Opening BC. But how do we know the exact VF at this boundary? (since the amount of air passing through this boundary depends on the liquid spray velocity which is not known accurately before the simulation)

Thank you!

[shivasluzz]

Regarding question no. 1:

I find the 'Turbulence induced breakup' option in Domain Particle injection, whereas in BC Particle injection, we need to specify the Particle mean diameter mandatorily.

What to do if we want to use the turbulence induced breakup with BC particle injection?

Thanks!

[ghorrocks]

Q3:

There are some cases where we don't know the VF before the simulation

I really meant what I said, it is the fundamental basis of boundary conditions. The whole point of a boundary condition is that you can define the flow conditions there. If you cannot define the flow conditions there then you cannot put a boundary condition there.

You can say, however, that the recirculating flow is going to have a VF close enough to zero that I will call it zero. That is what I recommend you do here. If this approximation is not accurate enough for you then you will have to move the boundary further away until it is accurate enough.

Q1: There are many ways particles can be generated. Particle breakup is one, and introducing them at boundaries is another. There are many, many more ways of generating them beyond this as well.

Or is your question "What to do if we want to use the turbulence induced breakup with BC particle injection?"