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-   -   Difficulties with viscoelasticFluidFoam solver (http://www.cfd-online.com/Forums/openfoam-solving/70447-difficulties-viscoelasticfluidfoam-solver.html)

titio November 24, 2009 18:43

Difficulties with viscoelasticFluidFoam solver
 
Hi foamers,

I am trying to use the viscoelasticFluidFoam to model the flow of complex fluids in microfluidic systems. To test the code, and to get an idea of its behaviour and performance, I am running the case of the flow between infinite plates, where several analytical solutions for different constitutive equation models are available.

So far, I got the following results of my comparisons.

- For low values of the Deborah number (De), simulated results agree well with the theory.
- When I increase the value of the De number, it starts to deviate, increasing the deviations with De.
- When I run the solver with a null value for the solvent viscosity, I only can get convergence for very small values of De.
-Depending on the value of the density, the solver converges or diverges.

I used the linear version of the PTT model in my simulations, based on the example given in the tutorial, changing of course the mesh.

After talking with some people with knowledge in the area, they refered that there may be a problem in the wall boundary conditions. In particular, for viscoelastic fluids it is not correct to impose zero gradient boundary conditions for the extra tension. I am reading the literature now concerning this question and it looks like one needs to implement specific boundary conditions in the walls for these fluids.

Does anyone has any idea what kind of boundary conditions I should use, and how to do it.

Thanks in advance for any assistance,

Regards,

Titio

ata November 25, 2009 05:19

Difficulties with viscoelasticFluidFoam solver
 
Hi titio
Thatís true. I already thought about this subject. In steady state you can use no-slip boundary condition in stationary walls and set div(tau)=-grad(p) that must be modified during the solving. I must tell you this is my opinion and I am not sure if it works or even correct.
Please inform me if it works.
Best regards


Ata

miael March 26, 2012 10:27

Hello everybody,

I just want o ask, if there is something new regarding theboundary conditions for viscoelastic simulations. I want to simulate a pipe-flow and I don't know, if my inletBC ( tau --> fixedValue uniform (0 0 0 0 0 0); ) and outletBC (tau--> zeroGradient;) are correct. For the walls I also use zeroGradient.

Thanks

Michael


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