Creating MRF/AMI Region


#1

Hello All,

I am new to simscale and have been going through the tutorials and some practice exercises. While I was trying to create a cell zone as a surface refinement for implementing AMI or MRF, the corresponding region is not created after the meshing process. Which I think is necessary to put in the rotation boundary condition in the simulation phase.

I am trying to simulate a rotating/pitching airfoil. I created a cylinder encompassing the airfoil and used this volume to create cell zone. I was wondering if I need to specify any other condition or setting to create the region.


#2

Hi @vt_vijay!

Could you share the project with us please? Either the @PowerUsers_CFD or me will have a look at it :slight_smile:

Best,

Jousef


#3

Thank you for getting back to me. I have sent an invite link to the project @PowerUsers_CFD. I am attaching the link to the project below as well
https://www.simscale.com/projects/vt_vijay/amitest/


#4

Hi @vt_vijay!

The side face of the airfoil is touching the cylinder - make sure to fix that first. Can you tell us why you put a cylinder for the MRF around your airfoil?

Cheers!

Jousef


#5

Hi @jousefm ,

Thank you for clearing that up. I thought that’s the way to assign an MRF/AMI volume to pitch the airfoil. Even in the tutorial shown for Hex-dominant parametric: Rotating geometries, a cylinder is used.
https://www.simscale.com/docs/content/preprocessing/meshing/snappyHexMesh-MRF.html

I am trying to simulate a 2D airfoil/infinite wing using the symmetry boundary conditions on the sides. I figured a cylinder of height same as the length of the airfoil should do the job because I would have to specify the boundary on the end face of the wing. If the cylinder needs to be bigger than airfoil, how do I modify the configuration to specify the symmetry boundary condition?
Is there another better way to do this?

Thanks,
Vishal


#6

Hi @vt_vijay,

This project is highly relevant to you. I suggest you keep the circle thin like in this project.

Good luck.

Regards,
Barry


#7

Hi @vt_vijay & @Get_Barried!

Darren (@1318980) did not use the same approach as Vishal. However I highly doubt that this approach will give you accurate results as you are influencing the whole domain around the airfoil resulting in a completely different study. That’s why I was curious and thought you are working with a paper or any other resource that came up with this idea. A straightforward approach would be to simply change the angle of attack by splitting the velocity components into x & y direction (assuming that z is the depth). However it is correct that this is not a real-time pitching/rotation of the airfoil.

Afaik Dakota provides realtime optimizations of your geometry by using coupling methods.Feel free to correct me if I misunderstood you or if you have any other questions!

Best,

Jousef


#8

Hi @jousefm and @Get_Barried,

Thank you for the project link and your thoughts. I was not sure if we could make the mesh one cell thick, but now I know. If I understand correctly, what @jousefm is saying is that the cylinder would affect the flow around the airfoil. I was under the impression that the cylinder is just to assign a volume during meshing and is not treated any differently during the simulation phase.

I understand that changing the velocity components would effectively change the angle of attack. But the idea is to eventually simulate a flapping wing with multiple degrees of freedom and analyze that. I thought a good starting point would be simulating 2D airfoils and then go from there. Right now I was trying to make an airfoil pitch up and down and analyze the transient performance of the airfoil. Is that not possible on simscale? Or is there another approach to tackle this problem?

Thank you guys for helping me out,
Vishal.


#9

Hi @jousefm & @vt_vijay,

Ah I read it differently. Thanks for the clarification Jousef! I had a classmate run the same simulation but with only the front circular so I assumed it could be similarly done.

I think I can get what you’re trying to do but I highly doubt that is possible in SimScale. In ansys I have seen such functions where you can pitch an aerofoil the way you wanted to analyze it but not on SimScale to my knowledge, maybe Jousef you have an idea if its possible at all here?

Cheers.

Regards,
Barry


#10

Hi guys,

by using AMI it maybe could work but I never tried it myself to be honest. Maybe Darren (@1318980) has done some tests and can tell if there is a way to achieve this instead of using different angles all the time.

Cheers!

Jousef


#11

Hi @vt_vijay, @jousefm and @Get_Barried, I see no issue with rotating the aerofoil transiently using the AMI, you will need to be a bit cleaver in defining the angular velocity as a .csv to move it as you want to, doing some hand calculations to know the rate of rotation to get the aerofoil from angle A to angle B. Also you want to leave the solver to reach steady flow before you start moving it. I would suggest making a really coarse mesh (but refined at the AMI boundary of course) to test your setup and once it works then make a finer mesh as this is likely to be computationally intensive, so running it once is ideal :slight_smile:

One last word, maybe run the sim with AMI rad/s = 0 to start to ensure boundary conditions all agree.

Kind regards,
Darren


#12

Ps. @vt_vijay I noticed your rotating zone wasn’t meshing so I just adjusted it slightly and now it appears:

https://www.simscale.com/projects/1318980/amitest/

and also the layers haven’t inflated, you might need to alter some quality setting in the operation to get them to inflate with the final layer thickness of 0.03 relative.

Kind regards,
Darren


#13

Hi Guys,

Thanks for taking the time to clear this up. @1318980, I was looking at the changes you made and I saw that the background mesh was made a bit smaller. I thought the background mesh had to surround the geometry. The region is created and I can use the AMI now.

Thanks a lot for your help. You guys are awesome, will comeback if I am stuck again.

Cheers
Vishal