# Propeller validation: Problem with mesh independence

**URL:** <https://www.simscale.com/forum/t/propeller-validation-problem-with-mesh-independence/82268>\
**Category:** Project Support\
**Created:** [April 16, 2018, 6:18pm UTC](https://www.simscale.com/forum/t/propeller-validation-problem-with-mesh-independence/82268 "2018-04-16T18:18:16Z")\
**Posts on this page:** 1\
**Showing post:** 9

<div class="post-metadata">

**Author:** ![Filiptheking](https://www.simscale.com/forum/user_avatar/www.simscale.com/filiptheking/32/18726_2.png) [@Filiptheking](https://www.simscale.com/forum/u/Filiptheking)\
**Post date:** [April 18, 2018, 3:11pm UTC](https://www.simscale.com/forum/t/propeller-validation-problem-with-mesh-independence/82268/9 "2018-04-18T15:11:52Z")

</div>

> [@Get\_Barried](#):
>
> If it does apply properly, you would see the edges having smaller cells than the center (refer to the figure below, feature refinement on my wing geometry). Instead it seems to be just refining your MRF only which quite perplexing.

It did actually refine close to the propeller blades too, so it was not only at the MRF-zone. The problem is that it seemed to refine over the surfaces and not only the edges. Which is very weird, indeed.

Without feature refinement (Mesh: FS: APC-SF-8x3.8 Mesh lvl 1 ):

 ![1](https://www.simscale.com/forum/uploads/default/original/3X/2/f/2f7113f7cd6ebd76ede8cff43ad1be1752ea4669.PNG)  
With feature refinement (Mesh: TAKE 2: lvl1v1):  
 ![2](https://www.simscale.com/forum/uploads/default/original/3X/e/5/e58f16dbab7595e49f4231330d2b11302b82017b.PNG)

(The mesh clips are from this study: [Mesh independence study 2 - Take 2](https://www.simscale.com/projects/Filiptheking/propeller_validation-_mesh_independence_study_2/), apart from the feature refinement, they are similar)

> [@Get\_Barried](#):
>
> They don’t fail, instead they get deleted by the quality controls. This post here should help in fixing that.

_Min tetrahedron-quality for cells_ was already set to -1e+30 in my mesh. However, I tried to change the _Min Cell Volume_ to -1e+30, which was suggested by @1318980, in [link](https://www.simscale.com/forum/t/inflate-boundary-layer/77211/3) you provided.  
This seemed to fix the problem with the inflate boundary layers, which I’m very grateful for. Thanks!

I tried this on another mesh that I had problems with the inflate boundary layers on.

Mesh with _Min Cell Volume_ = 1e+13

 ![1](https://www.simscale.com/forum/uploads/default/original/3X/4/3/434a4dcfcd5bf4618b98a0ca6f7a4fc0469b46ee.jpg)

Mesh with _Min Cell Volume_ = -1e+30 and three inflate boundary layers

 ![2](https://www.simscale.com/forum/uploads/default/original/3X/1/f/1f0d19548590dc522a2c4b2a1bd1d7e5f4d16fae.PNG)

Mesh with _Min Cell Volume_ = -1e+30 and five inflate boundary layers

 ![3](https://www.simscale.com/forum/uploads/default/original/3X/6/b/6bb6d38259746eb71b3020d258a6f0a2a08df453.PNG)

I think these last two meshes looks pretty good. Instead of a feature refinement, I’ve used a really fine surface refinement on the propeller blades. This gives me some unwanted refinement over the surfaces, ideally, I would of course only want refinement on the trailing and leading edge. But at least this works better than the feature refinement, for now.

Some of the settings for the mesh on the previous picture:

- Base mesh box = 21x21x21 (Will probably try to increase this to hopefully get better convergence)
- MRF refinement = 4-4
- Blade surface refinement = 9-9
- Mesh with Min Cell Volume = -1e+30
- Setting for inflate boundary layers:
  - Number of layers = 5
  - Expansion ratio for layer cell thickness = 1.3
  - Thickness of final layer = 0.00008729
  - Minimum overall layer thickness = 0

  

Link to project with the meshes on the three pictures above: Propeller Meshing: [Test with no Minimum Cell Volume](https://www.simscale.com/projects/Filiptheking/validating_the_flow_around_an_apc_slow_flyer_propeller_-solve_it_with_simscale-_8/)

**Some questions**

1. Could the method I use in the last mesh be a good alternative to the “feature refinement method”, if we don’t get that to work properly?
2. Do you need any refinement in the region between the MRF and the mesh outside of it? On the mesh described above, it looks like the picture below.
3. Up until now, I’ve been using wall functions as my wall treatment. Is it possible to have the inflate boundary layers to fine for the wall functions to work?

 ![4](https://www.simscale.com/forum/uploads/default/original/3X/a/5/a503b04330eaaf96bcd15b4f529fb5b710ebc272.PNG)

---

_[View the full topic](https://www.simscale.com/forum/t/propeller-validation-problem-with-mesh-independence/82268)._