Tagged: boundaryconditions, cfd, cfx, periodic, workbench


May 28, 2021 at 5:29 amP_HengSubscriber
Hello everyone, have a good day.
Can you recommend me what boundary condition can I use instead of periodic boundary condition? I ever used the periodic boundary condition and I can use this boundary because Both interfaces are the same.
But I now have one more domain which their interfaces are not the same as you see the uploaded picture. I need to do the case like periodic case but I cannot use the periodic boundary condition for this domain.
I want to know that what boundary condition can I use instead of periodic boundary condition?
My regards,
P_Heng.

May 28, 2021 at 2:17 pm

First, I want to tell you that I have a whole domain, and the picture which I sent to this forum is the section. 1/8 section. I will send the whole domain now.
My ProfessorÔÇÖs idea, he wants me to use the periodic boundary condition and I have to put the value for gravity = 1 , viscosity = 1 , and density = 1 only. I must be allowed to put the values of velocity.
I can use the periodic boundary condition for the whole domain and for the 1/4 section of the domain. But I cannot use this boundary for 1/8 section of domain because both interfaces are not the same.
I also try to use the symmetry boundary condition but the result (volume average of velocity) of 1/8 section is too different to the 1/4 section and the whole domain. The result of 1/8 and whole domain are the same.
I donÔÇÖt know what boundary should I use because I donÔÇÖt know the value of velocity. If I use the periodic boundary condition, I donÔÇÖt need to put the value of velocity.
Are there more solutions?
My regards P.Heng.
For my domain, if I cut the domain into 1/4 section, it can be use with the periodic boundary condition and symmetry boundary condition. But my professor want me to cut it into 1/8.
My regards P.Heng.
Regards Ishan.
I use CFD (setup fluent).
My regards P.Heng.
Regards Ishan.
Tomorrow, I will send you the maximum value of velocity and the volume integral of velocity for whole domain and 1/4 section of domain.
I cannot send you now because I use the computer in my lab and I am now in the dormitory. Now, it is 11:00pm.
My regards P.Heng.
Regards Ishan.
Thanks for your suggestion.
My regards, P. Heng.
This is my first to ask the question in the forum. IÔÇÖm sorry for choosing the wrong option to ask the question.
Again, thanks for your time.
My regards P. Heng.
Karthik
Thanks for your response.
For 1/8 section of domain, I want the fluid flow in the z direction because I put the gravity in z direction. Therefore, inlet and outlet are in z direction.
For other interfaces, I use the symmetry boundary condition and the inside curve is solid.
Anyway, I cannot use inlet velocity and pressure outlet because I am not allowed to put the value of velocity by myself. This is the nature fluid flow.
First time, the researchÔÇÖs purpose uses the periodic boundary condition. But I have no idea when the domain is cut into 8 sections as I sent the pictures above.
My regards P. Heng.
Thanks for your response.
My regards P. Heng.
Thank you.
My regards P. Heng.
Are there any ways to write the UDF for the boundary condition that we can use instead of periodic boundary condition but that boundary condition have the same role as the periodic boundary condition? In the case, the domain have the different faces.
My regards P. Heng.
Thanks for your response and your time.
My regards P. Heng.
Because my domain is not periodic, What boundary condition can I use?
In my case, I have gravity = 1, density = 1 ( boussinesq ), viscosity = 1.
I donÔÇÖt have the value of velocity or pressure.
My regards P. Heng.
I am happy to see your response.
I ever try to use the symmetry boundary condition but if I compare the result of velocity between 1/8 domain and 1/4 section of domain or whole domain, their results are too different.
Whole domain and 1/4 section of domain have the same result.
My regards P. Heng.
I want the result of velocity of whole domain, 1/4 Domain, and 1/8 domain are the same.
The purpose of my professor is that he want me to cut the domain into 8 sections in order to reduce of using many nodes and elements.
Therefore, their result should be the same.
My regards P. Heng.
I am happy to see your response.
The result of maximum velocity and the volume average of velocity for whole domain and 1/4 domain are the same because they able to use with periodic.
But their results are different from 1/8 domain because 1/8 cannot use the periodic boundary condition and I try to use the symmetry boundary condition.
I think that they, whole domain, 1/4 domain, 1/8 domain, should have the same result.
As you see in the picture, the vector of velocities are weird in the case of using symmetry boundary condition.
I will send you the pictures of 1/8 domain and 1/4 domain.
My regards P. Heng.
What does now your Prof want you to do? CAn you just share the 1/4 geometry and 1/8 geometry mesh picture (learn how to make good screenshots like using Snipping Tool) :)
Let's just focus on the whole case: can you list settings, models used, Equation of State, Gravity On/Off, etc.. and then tell us more about convergence? Does your Prof require your efforts to finish his slides for the lecture?
My professor wants me to run the flow for the porous media. For my case, I donÔÇÖt know the value of velocity because this is the natural flow in the ground.
what I can put in Ansys Fluent are: gravity = 1 [m/s2], density = 1 [kg/m3] (boussinesq), and viscosity = 1 [kg/ms].
Before, I started to study the 3D geometry, I ever try to calculate 2D geometry with the simple rectangle shape in the purpose to compare the result of velocity between the Ansys and hand calculation.
For this 2D geometry, I also used periodic boundary condition and its result is the same with the hand calculation, 100%.
when I start to study 3D geometry, I do everything like I did for 2D geometry.
As the results, Whole domain and 1/4 domain have the same result, velocity and the volume average of velocity.
My professor wants me to run 1/8 domain. As you see in the pictures, I cannot use periodic anymore. He wants me to use the other boundaries and he called it, implied boundary condition.
I ever try to use symmetry boundary condition but the result cannot be acceptable and the vector of velocities are weird.
I want to know what boundary condition can I use instead of periodic boundary condition or what should I do to get the same result.
I will send you the pictures below.
I answer your other question. This is my research. It is not for the lecture. I use Laminar flow and the energy is on. The gravity is on and its value is 1 [m/s2].
For calculation: Number of iterations = 200, Reporting Interval = 1, Profile Update Interval = 1, Time Scale Factor = 1. When I run the calculation, the solution is converged around 30 solution (30 solution is converged)
My regards P. Heng.
Yes, I do.
I ever discuss about this with my professor but he still wants me to find the way to do it. Maybe, he have his own solution or something. I am not sure.
I agree with your idea. However, I will discuss with my professor again.
Thank you for your response.
My regards P. Heng.
I am sorry that I don't know the circulating periodic or one with loss.
When I create the periodic boundary condition, I see the Creation Method (option: Auto, conformal, Non Conformal) and the Type of Periodic Boundary Condition (Option: Translational, Rotational).
My regards P. Heng.
My professor said that, there is no inlet nor outlet. The flow field is produced by the gravity.
how do you think about this idea?
My regards P. Heng.
Buoyant flow also implies heat is being added into the domain, or that a heavier phase is draining through a structure. That's definitely not periodic.
My regards P. Heng.
Thanks for your time and response.
My regards P. Heng.
Yes, I see.
Thank you.
My regards P. Prosheng.
Yeahh loll.
Thank you.
My regards P. Heng.
I am happy to see your response again.
My professor didnÔÇÖt say anything relative to this mesh.
According to ansys manual, the velocity should be zero at symmetry boundary.
My regards P. Heng.
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