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-   -   Passive scalar transport (http://www.cfd-online.com/Forums/openfoam-solving/58092-passive-scalar-transport.html)

novyno May 8, 2008 13:06

Dear Foamers I have a littl
 
Dear Foamers

I have a little question about the passive scalar transport. I molelled a mixture of N2 and O2 like a carrier flow and the concentration like a passive scalar. I have this boundary condition:

- A pressure inlet where I know the concentrations

- A first O2 (only) outlet where I know the mass flow rate

- A second outlet (N2 + O2) where I know the mass flow rate but not the concentration.

At inlet always is ok --> I define pression and concentration

At the second outlet always is ok --> I define velocity (concentration is calculated)

At the fisrt inlet ??? --> I define velocity but I don't know wath kind of boundary condition I have to assign for the concentration.

I suppose N2 density and O2 density are the same, so the fluid density and the fluid properties are constant and the concentration is completly indipendent from the flow (only use U to solve the transport equation).

My solver is a modified version of icoFoam (icoFoam + passive scalar transport equation for the O2 concentration).

Can someone help me?

novyno May 13, 2008 10:30

I have resolved my problem. I
 
I have resolved my problem. I have assigned the flux at the oxigen oultet.

If someone have the same problem contact me...

jaswi May 13, 2008 10:50

Hi Valerio if possible, ple
 
Hi Valerio

if possible, please provide an email address in your profile so that others users could contact you with request on similar problems.

With Best Regards
Jaswinder

jaswi May 14, 2008 09:40

Thanks Valerio Jaswi
 
Thanks Valerio
Jaswi

pavel August 6, 2008 08:57

In my diploma thesis I simulat
 
In my diploma thesis I simulate the mixing process in a T-shaped
> micro-mixer (width 200?m, height 100?m). The flow is laminar
> (steady-state) thus I am using the simpleFoam solver and I've added the
> scalar transport equation
>
> fvm::ddt(C) + fvm::div (phi,C) –fvm::laplacian(DC,C)
>
> in the solver in order to solve the species equation and calculate the
> concentration field in the mixer.
>
> The scalar is released at the inlet 2 (C=1), and at the inlet 1 (C=0,
> dimensionless) there is no scalar. The boundary condition for the
> velocity is a parabolic velocity profile (Umax = 3.29m/s at the Inlet 1
> und -3.29 m/s at the Inlet 2). At the outlet I am using zeroGradient for
> velocity und fixedValue (0) for p (pressure). The cells size is 4?m -
> 4?m - 4?m (hex-cells).
>
> The problem is the following: the calculated concentration must be
> between 0 and 1 but I receive values from -0.16 until 1.16.
>
> I've tried the following steps:
>
> 1) div (phi,U) Gauss limitedLinearV 1.0;
> div (phi,C) Gauss limitedLinear 1.0;
> laplacian (DC,C) Gauss linear corrected;
> Result: C = -0.153 – 1.08, but the physical sense of mixing is not
> correct (compared to simulation results using CFD-ACE+ and experimental
> results)
> 2) div (phi,U) Gauss linear;UpwindV Gauss;
> div (phi,C) Gauss Gamma01 1 Gauss;
> laplacian (DC,C) Gauss linear limited .0;
> Result: C = -0.17 – 1.07, the physical sense of mixing is better than > 1) but is not correct too.

> > 3) div (phi,U) Gauss linearUpwindV Gauss;
> div (phi,C) Gauss linearUpwind Gauss;
> laplacian (DC,C) Gauss linear corrected;>
> Result: C = -0.157 – 1.16, the physical sense of mixing is *correct*
> (compared to simulation results using CFD-ACE+ and experimental results)
> but C is not between 1 and 0
>
> *fvSolution file for all cases*:
>
> …
>
> C PBiCG
>
> { tolerance 1e-06;
>
> relTol 0;
>
> preconditioner DILU;
>
> };
>
> …
>
> RelaxationFactors
>
> P 0.3;
>
> U 0.7;
>
> C 0.7;
>
> …
>
> *fvSchemes:*
>
> …
>
> fluxRequiment
>
> { default no;
>
> P;
>
> C; (here I've tried with and without C - I cannot see any difference)
>
> How can I improve my results from approach #3, so that my concentration
> is in the boundaries between 1 and 0?


I would appreciate any advice

nicolai_heilskov January 16, 2009 05:35

Hi, Im using simpleFoam and
 
Hi,

Im using simpleFoam and want to include transport of a passive scalar. How and were shall I add the scalar transport equation. Do I need to add any thing else?

Any advice is appreciated.

nicolai_heilskov January 16, 2009 05:37

Hi, Im using simpleFoam and
 
Hi,

Im using simpleFoam and want to include transport of a passive scalar. How and were shall I add the scalar transport equation. Do I need to add any thing else?

Any advice is appreciated.

nandiganavishal January 16, 2009 14:33

Hi All, I am using coupled
 
Hi All,

I am using coupled Transport equations... I would like to add flux boundary condition at the walls of my geometry (which is square channel).

This is the equation i would like to add...

-D1*grad(C1) - K1*C1*grad(Phi) = 0
-D1*grad(C2) - K1*C2*grad(Phi) = 0

where C1 C2 and Phi are concentrations and potential respectively which I have obtained from solving my transport equation and poison equation (for Phi)...These equations are coupled...

I solved them using simple boundary conditions but I would like to solve them using the above mentioned flux boundary condition.. can anyone help me out with regard to this...

Thanks

Regards

Vishal

Susan YU June 26, 2009 04:59

hi, Andy, could you give me some suggestion on how to use passive scalar method in fluent? I'm fresh hand for this method, totally have no mean for it. I appriciate for your help.

aabbasi59 September 6, 2012 06:52

ScalarTransportFoam with a non-constant DT
 
Dear Friends,
I want to solve a very simple scalar transport problem(Heat transfer). The main issue is that the Diffusion Coefficient(DT) is not constant and is a function of z(in 1-D) and grad(T).In fact DT should represent the effects of stability(Richardson Number) in the heat transfer model.(see the link: http://dl.dropbox.com/u/93154655/HeatTransfer1D.pdf).
I defined the necessary fields but it seems that this solver doesn't work with a non-constant DT?!!
Does anybody have an idea about it?
Thanks in advance.


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