[novyno]

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]

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

If someone have the same problem contact me...

[jaswi]

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]

Thanks Valerio
Jaswi

[pavel]

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 -à 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]

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]

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]

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]

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]

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.

[cute]

Originally Posted by aabbasi59

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.

Did you get the solution? I am having a same problem.