[sheth]

Hi,

I am trying to model flapping motion of airfoil. My questions are

1. After some iterations there is negative volume error being generated so what should I do to avoid that.

2. Is my meshing scheme suitable for capturing flow perfectly (Image attached).

3. How do I mesh so that when flapping occurs in solver there is no negative element. Or any remedies for such problems.

4. I tried the remesh option available in cfx solver, but it rotational displacement about centroid or any other point is neglected in remeshing. See image [its from cfx manual], so any solutions?

Any help will be appreciated.

Thanks for time.

[PSYMN]

If you mean that you move the nodes of the airfoil and that causes them to collapse elements in the direction they are moving, I would say you need to work on your morphing skills...

The morph needs to be interpolated over a larger range than one element... This way, as you move the airfoil, the displacement will be shared over a much larger range and all the cells in that range will only be affected by a small amount...

If the CFX solver has this capability, you may just need to learn to use it properly. Try asking this question in the solver forums instead...

How ever, I can tell you that the mesh is not sufficient, even for a stationary wing... Most of the interesting stuff should happen close to the airfoil surface (the boundary layer) or in the wake behind the airfoil. You have insufficient mesh resolution in both of these areas...

[diamondx]

Here's a link of Mr simon performing a mesh around an airfoil. it's very well explained get some inspiration from there, hope it will help:
http://www.youtube.com/watch?v=tYrbScUH9RE

[sheth]

I agree with you both. I have kept meshing quality so low because I wanted to test if the mesh motion commands in cfx are working or not so I kept low mesh elements to reduce computation time. But should I opt for any special type of mesh if my airfoil has translational and rotational motion.

Originally Posted by PSYMN

If you mean that you move the nodes of the airfoil and that causes them to collapse elements in the direction they are moving, I would say you need to work on your morphing skills...

The morph needs to be interpolated over a larger range than one element... This way, as you move the airfoil, the displacement will be shared over a much larger range and all the cells in that range will only be affected by a small amount...

If the CFX solver has this capability, you may just need to learn to use it properly. Try asking this question in the solver forums instead...

How ever, I can tell you that the mesh is not sufficient, even for a stationary wing... Most of the interesting stuff should happen close to the airfoil surface (the boundary layer) or in the wake behind the airfoil. You have insufficient mesh resolution in both of these areas...