Questions about creating 3D cylindrical meshes or simulating flow past a sphere in Nek5000 v19.0

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Yinglu Peng

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Oct 23, 2025, 9:04:26 PMOct 23
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Hello,

I’m a new Nek5000 user working on 3D simulations and have two questions:

1. 3D cylindrical mesh
I would like to know how to create simple curved geometries such as cylinders or rings in Nek5000 v19.0.

  • How can I create a 3D cylinder with curved sidewalls?

  • Is it possible to build the geometry in ICEM (or another external meshing tool) and then convert it using exo2nek?

2. Flow past a sphere
I found the 2D example “flow past a circular cylinder”, but there doesn’t seem to be a 3D version for a sphere.

  • In Nek5000 (2D or 3D), how can I create a circular or spherical region inside the fluid domain?

  • I’m a bit confused about the workflow or steps to generate such geometries.

If there are any guides, examples, or recommended workflows for this, I would really appreciate your help.

Thank you very much!

YuHsiang Lan

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Oct 24, 2025, 10:58:22 AMOct 24
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Hi,

You can use our meshing tools 
  genbox  ! box, cylinder, etc
  prenek   ! graphic interface, has some sphere object in it
  n2to3     ! extrude 2D mesh to 3D mesh
or import meshes from other format
  gmsh2nek
  exo2nek

We have some documentation here:

For a straight cylinder, I'd suggest start from a 2D mesh and use n2to3. 
You can find existing meshes for flow in a pipe or flow past a cylinder.

We also have "hemi" example for flow past a hemi-sphere. 
You can use prenek to reflect and duplicate it to make it a whole sphere.

I also have my MATLAB script for those two as well. Feel free to have a look.

One extra detail. Usually, re2 store the mid point of the curve, "m", to make the curves quadratic polynomial.
If you want higher accuracy, you might want to either using high-order curved side for cylinder or sphere, "c" or "s", or re-project the grid points in usrdat2.

Hope this helps,
Yu-Hsiang
--

Yinglu Peng

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Nov 1, 2025, 12:43:57 PM (13 days ago) Nov 1
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Hi!

I’m currently generating a geometry where the circle size depends on its radius.
I plan to use genbox followed by n2to3 for the mesh generation.

However, I encountered an issue when trying to open Prenek — it fails to display properly (blank/red window) even after switching to Xorg on Ubuntu 24.04 (VMware Workstation 16 Player).

Although Prenek is no longer updated, it’s still helpful for checking and visualizing the mesh, so I’d like to get it working if possible.
Has anyone run into this issue or found a workaround?

Best regards,
Yinglu Peng


YuHsiang Lan 在 2025年10月24日 星期五晚上10:58:22 [UTC+8] 的信中寫道：
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