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Tunnel Jet fans

29 REPLIES 29
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Message 1 of 30
Berkan_vent
2107 Views, 29 Replies

Tunnel Jet fans

Hi everyone,

 

i want to ask a question about my model that related about tunnel ventilation system.

 

As you know tunnel needs ventilation. For this reason i want to use jet fans for my model. In material tab, i see internal fan/pump. Can i use it for my model? or do i need to use different thing?

 

if i use internal fan how should i describe boundary conditions?

 

Thank you so much.

29 REPLIES 29
Message 2 of 30
Jon.Wilde
in reply to: Berkan_vent

Hi,

 

I would say it is best to model the jet fan casing, leaving it hollow and placing a cuboid at the beginning of the outlet (not at the outlet) which you would assign as an axial fan, with no RPM (as it is not cylindrical).

You should then add meshing region to the outlet(s) to be sure that you capture the jet well.

 

Does that make sense?

 

Kind regards,

Jon

Message 3 of 30
Berkan_vent
in reply to: Jon.Wilde

Hi Jon,

 

First of all thank you so much your reply But actually i dont understand very well sorry.

 

You said " placing a cuboid at the beginning of the outlet (not at the outlet)" I'm sorry but  I didnt understand "not at the outlet" part.

 

I attached my model and pictures of jet fan so you can see them clearly.

 

* My jet fan model is solid and i put steel material on surface. and fluid (Air) for entire volume.

* Boundary conditions: Inlet Volume flow rate, outlet: Velocity.

 

Thank you so much,

 

Berkan

Message 4 of 30
Jon.Wilde
in reply to: Berkan_vent

Hi Berkan,

 

Apologies, I had this type of fan in mind for some reason but I realise now that is not the case.

 

For your model, just model it as is in reality. Build the solid shroud (which you will suppress from the mesh) and model a cylinder inside it, which will be the fan. You need to apply the axial fan material to this.

 

Regarding your overall model, is there a reason why you have slip/symm applied to everything? I would delete all of those (you cannot have internal Boundary Conditions anyway) and then suppress all solid parts also, no need to mesh them.

 

Kind regards,

Jon

 

Message 5 of 30
sahar.rubin
in reply to: Berkan_vent

hi!

i'm using the software to simulate smoke exhaust from parking lots and i'm using the fan you added here, and i want to know how can i simulate it??
could you upload a CFD file so i'll see where i'm going wrong??

 

i'm adding my parking lot simulation, it'll be amazing if you'll take a look and have some comments how to make it better.

 

thank u!!!

Message 6 of 30
Jon.Wilde
in reply to: sahar.rubin

Hi Sahur,

 

Please could you share a CFZ file? We cannot open a CFDST file.

What makes you think you are doing something wrong? Please could you share some specifics?

 

Kind regards,

Jon

Message 7 of 30
sahar.rubin
in reply to: Jon.Wilde

First of, thank you so much for the fast reply!!

now, i'll explain myself better:

the project is a parking lot with 3 inlet fans (26000 cfm each), and 3 outlet fans (also 26000 cfm each)
there could be infiltration from the ramp but i don't really know hoe to do it..


there are 5 induction jet fans close to the lot's roof (exactly as this one, with these specifications)

 

the outside air temp is about 30 degrees Celsius (for now there is no temperature difference, only flow cfd's)

 

materials:

the walls/rooms made of standard concrete.

the ducts/volume/jets = air (variable).

 

Boundery conditions:

3 ducts inlets: Flow rate: 26000 cfm, Temp: 30 degrees Celsius.

3 ducts outlet: 0 Pa gage.

5 jets outlets: Flow rate: 2.7 m3/s, Flow velocity: 30 m/s (as referenced).

 

mesh sizing = automatic.

 

solve:

steady state.

100 iterations.

flow rate=on.

 

i tried doing as you said about the jets but i didn't really understood what you ment, and when i try the software puts a warning that it can't create such material because the subject doesn't recognized a nearby fluid or something like that..

please take a look at the file and tell me how to improve.

thanks a lot!!!!!!!!!!!!

 

Sahar,
Mechanical engineer

 

 

Message 8 of 30
Jon.Wilde
in reply to: Berkan_vent

Hi Sahar,

 

I took a look at your file, here are some pointers:

 

  1. Suppress all of the solid parts, they are not needed unless we are looking at conduction through them and instead just slow down the analysis
  2. You cannot assign internal boundary conditions - all of these need to be removed or modified. What you need to do is suppress the blocks that they are attached to - even better is to recess them into the block, to simulate the actual duct outlet.
  3. An automesh will be insifficient, please see the attached pdf. You will need to refine the air in general I would have thought. 4-5 elements across any ducts is a good starting point.

That ought to get your model running I hope.

 

Kind regards,

Jon

Message 9 of 30
sahar.rubin
in reply to: Jon.Wilde

thanks again!!!..

what do you mean by internal boundery condition? and do you have a pdf like that for ventilation and/or fire exhaust in parking lots? (it looks great!)

 

sahar.

Message 10 of 30
Jon.Wilde
in reply to: sahar.rubin

Take a look at your first velocity BC's - they are inside the model but all the others are outside. This will not work.

 

Delete these, or suppress the block they are attached to. You would also need temps on these inlets.

Alternatively, use the approach I just posted, where you will be recycling the internal air, more like how jet fans work.

 

I don't have anyting else right now, I made that up today to answer your question 🙂

You are very close to having a working model, I do not think you need a guide to be honest.

 

Kind regards,

Jon

Message 11 of 30
sahar.rubin
in reply to: Jon.Wilde

you helped me a lot! thank you so much!!!!

i'll try accomplish what you said and post the results.

btw, a huge thumbs up for the presentation and the kind reply.
tnx again!!
Message 12 of 30
sahar.rubin
in reply to: sahar.rubin

hi!

sorry to bother you with all the questions but i really want to make a good simulation Smiley Happy

 

i did exactly what you said and an error message appears (attached)

 

the new .cfz file's also attached, please advice how to solve?

 

tnx a lot!!!

Message 13 of 30
Jon.Wilde
in reply to: sahar.rubin

Hi Sahar,

 

The error tells you what you need to know. You are assigning a fan to a part that is not next to a fluid. I think this is becase you tried to build the fluid in CAD, please correct me if I am wrong though.

When you bring the model through to CFD, just leave it as a sealed hollow and CFD will create the air for you, this will wrap around all internal components and you should then not have this error.

 

Kind regards,

Jon

Message 14 of 30
sahar.rubin
in reply to: Jon.Wilde

Just saw what you meant about a volume around and in the jets..
And obviously it worked 🙂

another thing...  what's the material of the jets out body?

Message 15 of 30
Jon.Wilde
in reply to: sahar.rubin

The material of the solid jet body does not matter, as they will be suppressed. The only time we need to worry about solid materials is when they are meshed and we are looking conduction through them or the wall roughness assigned to them.

 

Hope that helps.

Jon

Message 16 of 30
sahar.rubin
in reply to: Jon.Wilde

Great!!!

 

it really helped!

that last reply really set my mind straight (Finally 🙂 )

 

thank you very very much for all the help!!!
i'll publish the results  for others to study from and for your approval 😉

 

Message 17 of 30
sahar.rubin
in reply to: sahar.rubin

hi again 🙂

having a problem with meshing... getting preety frustrated with this...

did what was written in the warning, can you please take a look at the fila and advise what am i doing wrong (i used autosize after i tried refining the mesh and it also crashed..)

 

pls help!

 

 

Message 18 of 30
sahar.rubin
in reply to: sahar.rubin

i know tried to simulate only the jet and my results are a bit different.. could you please upload a zip file containing the .cad file and the .cfz file that did this?

Message 19 of 30
Jon.Wilde
in reply to: sahar.rubin

Hi,

 

Here are the files.

 

Thanks

Message 20 of 30
sahar.rubin
in reply to: Jon.Wilde

that's amazing!
thanks a lot!!!!!

and about the question before? (about the mesh errors)
what do you advise doing?


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