Dynamic Mesh Issues
 

Hello all,

I have been struggling with a dynamic mesh problem for some time now. The model is a 2D C-grid wrapped around an airfoil, the back 25% of which is a different patch: a flap, which I intend to rotate relative to the rest of the wing. The issue is that I cannot find a suitable diffusivity that will prevent the mesh from turning inside-out at the trailing edge. I have tried all of the solver and diffusivity options within the dynamicFvMotionSolver approach, and found that solver displacementLaplacian (using angularOscillatingDiscplacement in the pointDisplacement file) and diffusivity inverseDistance work best. However, the mesh is still very poor at the TE (see pic inverseDist-TE - zoomed in view of trailing edge). I am using OF 1.7.0.

I tried RBFMotion from 1.5-dev, which solved the TE problem but introduced additional problems at the wing. I set the focalPoint at the TE, with an inner radius equal to the flap size and the outer radius beyond the airfoil and then again with the outer radius halfway through the airfoil. Form the pics, it is clear that RBFMotion distorted the rest of the wing, regardless of inner/outer radius selections.

Is there another option available? I have seen discussion about overset grids, however it looks like this is not available. Has anyone dealt with a similar problem - moving part of a piece of geometry, but not the whole thing, and making the diffusivity work? Is there something that can be done using topological changes?

Thanks in advance for any tips/ideas.

Dan

Hi Dan,

I've never used RBF but was planning to in the near future. However, I was at a OF symposium in Delft last week and Hester Bijl (kind of developer of RBF) showed us that it would be possible to define several points around your object of interest to keep the mesh steady. Not sure how it works though!

Keep us updated on your progress!

Cheers,

Ralph

Hi Ralph,

Thank you for taking the time to reply. Maybe that multi-point feature is in development; the only point I can define is the focalPoint in dynamicMeshDict.

There must be another way to do this. There is a "frozenPointsZone" set of data that can be read from dynamicMeshDict courtesy of displacementLaplacianFvMotionSolver, however I have put tried everything next to the frozenPointsZone phrase (patch name, set of two coordinates to make bounding box) and though it runs there is no discernible effect. Would loading diffusivities from a file do it?

Thanks,

Dan

Maybe try to put the word "banana" at the position where you put your arguments. When you run the case you'll get an error with a list of possible/suitable arguments you can choose from.

Thanks to prof Jasak for the banana-trick :)

Ralph

Hi, have you solved your problem to define frozenPointsZone in dynamicsMeshDict? I encounter the same problem, http://www.cfd-online.com/Forums/ope...tml#post504572

Can you share your solution?

Hi, I'm afraid I was not able to make these methods work. RBF consumes a lot of computational power too, slowing down the simulation substantially. Good luck.