Dynamic mesh
 

hi, plz tell me how 2 decide dynamic mesh parameters? I m solving store separation problem in FLUENT!

i wanna use, remeshing + size function along wid smoothing if possible!

my mesh scale info is: min length = 0.0014 max length = 0.71

max cell skewness = 0.50

i m solvin 2D , unsteady problem!

plz help me......

thx

Hello guys.

I'm doing the same thing as Chaitanya and I have the same problems. I cant decide the dynamic mesh parameters. Has anyone some information about that ? If so, please help me...

Thanks

Dynamic mesh
 

earnest

Describe your problem in detail or you can search previous post.

regards
mvee

Firstly, thanks for response.

My project is about store separation in 2D. I have a NACA profile and a store under the profile. There is no pylon for simplicity. I have pressure far field around the profile-store and unstructured (triangle) mesh. The main point of the project is to release the store to free drop. During the drop, obviously, store will disturb the meshes around itself.

My problem is that I could not do "remeshing" while store is going down. I always take this warning from fluent that "negative volume detected" or "invalid number". And there is no new meshes.

1) My first question is; should I use the "unstructured mesh" as deforming in dynamic zones?

2) What kind of parameters I should enter as the dynamic mesh parameters?

3) Or generally, what should I do?

Some information about grid is;
mesh maximum lenght scale:0.00359616
mesh minimum length scale:2.584736
mesh maximum cell skewness:0.6560645

And I m using "spring-smoothing" and "local remeshing" method in dynamic mesh.

Hi earnest

Exactly similar tutorial has been addressed in Fluent dynamic mesh tutorial. Please look at it.

It is very easy to do dynamic meshing rather than sliding meshing (solid slides over solid). Smoothing and remeshing requires unstructured mesh while layering requires structured. If any how you are able to generate layering then it is the best option. Use fluent calculated skewness, maximum and minimum length scale. In addition you have to take care of time step which should be calculated from drop velocity and cell distance.

Hope you find useful.

Best wishes
mvee

hi! mvee, I have an idea that based on a simple quad-mesh and the smoothing-remeshing method, the negative volume mesh problem cannot be avoided. Could you confirm it? Thank you in advance!

The negative volume error may be due to you not defining the fluid domain as a "deforming" zone.

deforming? seek some more details
 

reply to Rhyno466
Could you give me some details on defining the fluid domain as a "deforming" zone?
In fact, I'm just a beginner and I have been trying to correct the negative volume mesh problem for two days.
I want to rotate the airfoil in a steady angular rate and use the dynamic mesh in Fluent to simulate it. But I keep get the negative volume mesh problem.
Could you take a look at my problem?
The first two attachments are my mesh which is just from the Fluent Tutorial 6.3. And my parameters related to Dynamic Model are followed in these attachments.
If you had some free time, could you take a look at my setup and give me some advice? Thank you in advance!

more captures for the last post
 

more captures for the last post

Hi aerosjc

Try with tri mesh as you are defining angular rotation of blades. If it is lateral / transverse motion then block mesh will be alright. Use tri mesh with smoothing and remeshing options.

Best wishes
Mvee

mvee, Many thanks to you! Other guys also give me the same advice.I'll try!

I would recommend using an unstructured triangle based mesh as well. If you really don't want to re-mesh the domain, you can try a couple of things. First, by default Fluent does not support spring based smoothing on non- triangular cells, so you have to activate the spring on all shapes option from the text command window by entering the following:

/define/models/dynamic-mesh-controls> spring-on-all-shapes

Now that the quad cells will spring around the airfoil, you need to define the deforming fluid zone. You do this in the same screen that you define your rigid body airfoil movement.

Thank you a lot! But I have already tried these method and I found that it made no difference in my case.
I'm trying create a new msh file using Gambit. This msh file I'm trying to create consists of a hybrid mesh zone. I mean that the inner is a quad-mesh and the outer is a tri-mesh. However, I encounter a problem. Because I need to move the inner mesh in synchronization with the airfoil by the definition of UDF and conduct the dynamic mesh method on the outer mesh, I should export the hybrid mesh separately to tell Fluent that there are two mesh. But I failed, Fluent can only confirm one hybrid mesh.
Could you give me some advice? Thank you in advance!
The msh file I just created is in the attachment.

You would need to define have 2 separate fluid zones. One for the structured near airfoil region and one for the unstructured far- field region. I dont know how to accomplish this task however so I am unable to give you any advice on the matter. However, once you have the two zones, I believe you can give the structured zone the same rigid body movement as the airfoil and then set the unstructured region as a deforming zone.

Thank you all the same! I'm trying to create a curve on the interface between the two zones. I guess this can help Fluent recognize that there are two zones.

Thank you! I've already created my msh file.

Thank you! I've created a hybrid mesh and I will try other method like only remeshing.

@aerosjc
any updates please?have you managed to solve your problem?

I have already solved my problem. I'm writing a summery. If you'd like to review my paper, I would send you a copy several days later when I finish it. I'm still a beginner, so please forgive my ignorance on this field. :)

Thanks alot aerosjc, it will be my pleasure to review your paper but few questions....

1. You have solved the problem only in 2D or have you also solved it for 3D?
2 How you have managed to solve the negative volume problem?
3.How you have separated the structured near wall zone from the unstructured outer region? Did you define two fluid zones?how you did it?