How to simulate air flowing through filter?

[Anonymous]

Hi, i have an enclosed room with an exhaust fan on 1 end and an opening with a filter on the other end. the filter is represented by a solid object placed directly in front of the opening. anyone knows how i can simulate air flowing through an opening with the filter? 

[Jon.Wilde]

Yes 🙂

Utilise a resistance material. You will need air on both sides of it though.

Also a good uniform mesh with 4-5 elements through it's thickness.

Probably best to utilise Advection scheme 5 too!

Thanks,

Jon

[Jon.Wilde]

Hey,

Did this work out OK?

Thanks,

Jon

[Anonymous]

hi Jon,

i select resistance material and it takes me to material editor. what do i select from there? what is through-flow k and normal direction 1k and 2k? do i need to change them? i have attached a screenshot as well as the specs for my filters in this mail.

thanks

Zack

[Jon.Wilde · Accepted solution]

The top one will be the flow direction you assign in the main window. The other two relate to the other directions normal to the flow.

So here, the x direction will have a permeability value, the y and z are pretty well closed off with high constant loss values.

Choose values you know - you may actually have to either ask the manufacturer for some data or calculate this by the looks of it. I suspect they will have a loss coefficient or similar.

If flow cannot move in the directions normal to the flow, use something like a constant loss of 1000, this will minimise the flow.

[Anonymous]

Thanks Jon, i'll try that out.

[Anonymous]

Hi Jon, do i set the values for normal direction 1K and 2K to 1000 as mentioned or 10000 as shown in your screenshot?

[Jon.Wilde]

1000 should be fine 🙂

[Anonymous]

Hi Jon,

I tried running the simulation, but the inlet flow is too high at a few points as shown in the iso volume scans, reaches over 300m/s after about 700 iterations. is this normal? if not what is the cause of it and how do i resolve it?

thanks

[Jon.Wilde]

My guess is that you need longer inlets and possibly a better mesh there also. Ideally we have inlet extensions that are 5x width in length.

[Anonymous]

the number of my inlet openings and sizes are fixed. how can i make a better mesh?

[Jon.Wilde]

Fixed, yes but there is quite a short distance between them and the boundary condition - I think this needs to be longer.

Once you have these new parts, you could assign them a finer mesh.

Can you share what the mesh looks like here now with a cut-plane showing 'shaded mesh'?

Thanks,

Jon

[Anonymous]

Hi Jon,

is what you said similar to creating an external air volume instead, which allows air to flow out of the inlet and outlet openings? or do i have to extrude the inlet and outlet openings in the 3D model before running it?

I have attached the mesh screenshot below. i used auto mesh,which gives me a mesh size of 4 as shown in the screenshot.

thanks

[Jon.Wilde]

Hi,

Not an external volume, no. Add 3D volumes to the inlets and outlets before moving into CFD.