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-   -   Boundary conditions in Fluent (https://www.cfd-online.com/Forums/fluent/30759-boundary-conditions-fluent.html)

Ankan Kumar January 7, 2003 15:21

Boundary conditions in Fluent
 
Hi

I am new to Fluent. Can anybody tell me how do I put a FULLY DEVELOPED inlet boundary condition for pipe flow in Fluent? The velocity inlet conditon gives me plug flow which is not what I want.

Thanks Ankan

Keil January 7, 2003 22:50

Re: Boundary conditions in Fluent
 
Hi,

All we can do such a thing is that we have to customize the boundary condition via User Defined Function(called UDF) . Or, how about extend the inlet to be fully developed flow?.

I mean , we make the inlet region(called entrance region, or inlet length , enctrance length) This length is given by Boussineq or Nikuradse in laminar flow . Latzko in turbulence. When we make this length ,Fully developed flow is got automatically. This way is the most easy way I guess.

Regards,

Alamgir January 10, 2003 21:08

Re: Boundary conditions in Fluent
 
For your help further just look UDF manul 1st-3rd chapters and you have a clear idea about your problem.

cheers

Alamgir

furqanrk March 20, 2016 12:13

Quote:

Originally Posted by Alamgir
;104033
For your help further just look UDF manul 1st-3rd chapters and you have a clear idea about your problem.

cheers

Alamgir


Dear expert.. I have to use Superficial gas velocity 0.0016 m/s. But In fluent we have to put Velocity Magnitude at VELOCITY INLET boundary conditions.( INLET VELOCITY) How can I calculate INLET GAS VELOCITY form superficial gas velocity??? ( Reactor dimensions are 20*5*50 cm W*D*L and inlet dimensions are 2.4*1.2 L*D )

maalan November 8, 2016 06:40

Quote:

Dear expert.. I have to use Superficial gas velocity 0.0016 m/s. But In fluent we have to put Velocity Magnitude at VELOCITY INLET boundary conditions.( INLET VELOCITY) How can I calculate INLET GAS VELOCITY form superficial gas velocity??? ( Reactor dimensions are 20*5*50 cm W*D*L and inlet dimensions are 2.4*1.2 L*D )
Hi Muhammad, I'm at the same point as you. Did you figure it out?

Cheers,
Antonio

furqanrk November 9, 2016 04:44

Quote:

Originally Posted by maalan (Post 624646)
Hi Muhammad, I'm at the same point as you. Did you figure it out?

Cheers,
Antonio

Yes, I have solve this question.

Superficial velocity is a velocity that gives the same mass flow rate at any reactor cross-section (or volumetric flow rate, we do not care about density is varying or not - superficial velocity is engineering value based on the mean values). Superficial velocity is just Q/A, i.e. volumetric flow rate / cross-section.
As you have circular cross-section for reactor and inlet, the area A is PI*D^2/4. Q is fixed (to hold continuity principle).
If you have superficial velocity = 0.0016 for reactor (r-r) cross-section, you have to convert it 0.0016*(PI * Dr-r^2 / 4)/(PI * Dinlet^2 / 4) = 0.0016*Dr-r^2/Dinlet^2. Both D values should be put in the same units!
If you have superficial velocity = 0.0016 for inlet, no conversion is needed.


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