Boundary Layer Does Not Form - Except When Default Settings Used

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Hi all, so yes, this post is to confirm that using STL exclusively seems to result in higher prism layer formation! Thanks again @Retsam

Details:

  1. Objective of my current exploration was to conduct MRF simulation on propeller to see how well SimScale predicts the thrust and torque characteristics. Before I can do that, a decent simulation mesh needs to be generated and this post was a result of problems encountered at this stage.

  2. As you would read above, there were several problems along the way, perhaps due to my inexperience with OpenFoam and SnappyHex. All along, I was working with IGES files and the best prism layer formation was about ~70% I would say (optimistically). I have tried both y+=1 and y+=100 types, 5 layers to >10 layers etc since the cause of the problems were not clear.

    image
    image302×273 29.4 KB

  3. Y+=1 mesh will be something like:
    Layer1------3.40E-06m
    Layer2------4.42E-06m
    Layer3------5.75E-06m
    Layer4------7.47E-06m
    Layer5------9.71E-06m
    Layer6------1.26E-05m
    Layer7------1.64E-05m
    Layer8------2.13E-05m
    Layer9------2.77E-05m
    Layer10----3.61E-05m
    Layer11----4.69E-05m
    Layer12----6.09E-05m
    Layer13----7.92E-05m
    Layer14----1.03E-04m
    Layer15----1.34E-04m
    Layer16----1.74E-04m

  4. After almost giving up, and with very few options left (haven’t tried cfmesh as I don’t think my laptop has enough RAM), I just thought of trying STL. But I was not able to import 2 solids in 1 file if I directly output from Autodesk Fusion360. Nevertheless, the prism layer formation was >90% for meshing without the MRF volume.

solid_0_stl_solid 293784 10 0.000309 93.1

Aside: Using STEP file, the formation was ~70+%.

A1_I1541_B2_TE141_A1_I1541_B2_TE43 193864 7.83 0.000262 78.9
A1_I1541_B2_TE141_A1_I1541_B2_TE50 277 0.17 1.3e-05 3.93
A1_I1541_B2_TE141_A1_I1541_B2_TE53 2524 1.19 4.62e-05 13.9
A1_I1541_B2_TE141_A1_I1541_B2_TE124 193794 7.83 0.000262 79
A1_I1541_B2_TE141_A1_I1541_B2_TE131 277 0.17 1.3e-05 3.93
A1_I1541_B2_TE141_A1_I1541_B2_TE134 2523 1.19 4.62e-05 13.9

  1. Luckily @Retsam replied my distress call on STL and I managed to combine 2 STL files by exporting them in ASCII format and copying and pasting one STL file to another using Notepad++. Great idea! You will have something like that:

solid PROPELLER [this is the 1st STL file]
facet normal -8.195655e-01 5.663210e-01 8.713685e-02
outer loop
vertex -1.877391e+01 1.240122e+01 8.000000e+00
vertex -1.874856e+01 1.238448e+01 8.347296e+00
vertex -1.796457e+01 1.354920e+01 8.151286e+00
endloop
.
.
.
endsolid
solid MRFVOLUME [this is the pasted-in 2nd STL file]
.
.
.
endsolid

And then save as “All Files” with the .STL extension. Then proceed to import into SimScale.

  1. With the MRF volume inside too, it works! Again, >90% of the prism layers generated:

solid_0_PROPELLER 297213 9.97 0.000308 92.7

I used very fine tessellation on the propeller (and reminder to self to scale down by 0.001 to work in m).

image
image1366×768 205 KB

Now, I can finally run the simulation knowing that I have a decent mesh. Hopefully.

Thanks @DaleKramer, @Get_Barried and @Retsam for the help.

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