Learning Forum

[ibrahimallam087]

Hello,

Im trying to simulate a flow over a submerged body in water at the same time the body injects air to the enclosure to reduce drag 

I dont know if its possible to simulate this way however i tried to simulate this but the enclosure does not identify the air entring in it 

[Rob]

Which models are you using in Fluent?

[ibrahimallam087]

Im using volume of fluid model with two phases primary as water and secondery as air and i made surface on the cylinder so the the air can go out from it as an inlet to the enclosure domain 

I specified it as outlet mass 

[Rob]

The air should be inlet mass? And volume fraction of air of 1. But, you're also going to need to resolve all of the bubbles if you're using VOF. 

[ibrahimallam087]

the air is inlet velocity but in negative beacuse the fluent read the inlet as its inlet to the body (i substracted the body at first its walls only ) and the volume fraction of it is 1 yeah, the problem is that no air is entring the enclusure from the inlet holes which in the body and the air is entring only from the main inlet ,

[Rob]

If air is only entering at the water inlet check how you assigned the phases. Please also add some images as I didn't follow most of what you posted. 

[ibrahimallam087]

 

im trying to make here a sort of ventilated cavity 

 

[ibrahimallam087]

 

 

here is my problem the water enter from main inlet with velocity of 6 m/s  and exit as outlet pressure 
and there as a mass flow outlet from the cylinder as indicated with 0.0005 kg/s air 
the problem is the air doesnt enter the domain 

 

[ibrahimallam087]

im trying to vary the intlet of the cylinder as velocity inlet with negative values or pressure inlet but still there is no air entring the domain from cylinder at all

[Rob]

The cylinder would have a normal velocity of 6m/s or x-magnitude of -6m/s can you confirm? Also, VOF velocity inlets must be all of one or other phase, so you'd have a velocity inlet for the water and pressure outlet at the other end. 

[ibrahimallam087]

the cylinder has an inlet to the enclsure with mass flow rate of 0.0005 kg/s (Air),Another inlet to the enclosure is water as indicated with velocity of 6m/s normal to the boundary,the outlet is outlet pressure type with gauge pressure 40000pascal

[ibrahimallam087]

this is the cylinder input to the enclosure i splitted that face from the geometry and names it as an intlet and substracted the cylinder from the enclosure , so is this right ? cause the it gives me floating point error and the air is not entring the enclsure from the cylinder

[Rob]

OK, and at that flow rate do you expect to form a film, or small bubbles? Have you patched in a layer of gas adjacent to the inlet? 

[ibrahimallam087]

no i didnt patch gas , i just expect it to make cavity of air inside water to reduce drag of the cylinder

[Rob]

Try patching a layer of gas, but also check you have sufficient mesh to resolve the film or bubbles. About 10 cells across the bubbles or film ought to do it: aspect ratio as near to 1 as possible.