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Active Contributor
Berkan_vent
Posts: 28
Registered: ‎11-22-2013
Accepted Solution

Tunnel Jet fans

706 Views, 29 Replies
11-23-2013 07:22 AM

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.

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Product Support
wildej
Posts: 961
Registered: ‎08-25-2011

Re: Tunnel Jet fans

11-30-2013 11:43 AM 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



Jon Wilde
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Active Contributor
Berkan_vent
Posts: 28
Registered: ‎11-22-2013

Re: Tunnel Jet fans

12-01-2013 10:58 AM in reply to: wildej

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

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wildej
Posts: 961
Registered: ‎08-25-2011

Re: Tunnel Jet fans

12-02-2013 02:37 AM 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

 



Jon Wilde
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Active Contributor
sahar.rubin
Posts: 31
Registered: ‎12-03-2013

Re: Tunnel Jet fans

12-09-2013 02:46 AM 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!!!

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Product Support
wildej
Posts: 961
Registered: ‎08-25-2011

Re: Tunnel Jet fans

12-09-2013 03:13 AM 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



Jon Wilde
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Active Contributor
sahar.rubin
Posts: 31
Registered: ‎12-03-2013

Re: Tunnel Jet fans

12-09-2013 03:58 AM in reply to: wildej

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

 

 

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Product Support
wildej
Posts: 961
Registered: ‎08-25-2011

Re: Tunnel Jet fans

12-09-2013 04:33 AM 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



Jon Wilde
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Active Contributor
sahar.rubin
Posts: 31
Registered: ‎12-03-2013

Re: Tunnel Jet fans

12-09-2013 04:42 AM in reply to: wildej

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.

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Product Support
wildej
Posts: 961
Registered: ‎08-25-2011

Re: Tunnel Jet fans

12-09-2013 04:47 AM 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 :smileyhappy:

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

 

Kind regards,

Jon



Jon Wilde
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