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[ANSYS Meshing] Bidirectional Vortex Rocket

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Old   July 27, 2024, 18:10
Default Bidirectional Vortex Rocket
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I am designing a bidirectional vortex rocket motor and analyzing the combustion inside it. It consists of four tangential oxidizer injectors at the end of the chamber just above the outlet, four radial fuel injectors at the head end and axial oxidizer injector at the top of chamber. I am applying inflation to cover the boundary layer and multizone meshing to the chamber wall and outlet. the injectors are meshed using sweep and tetrahedron meshing. the problem arises with my solution. It fails even in initialization. I am using non-premixed species modeling for combustion.
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Old   July 29, 2024, 03:29
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Do you have a problem with the meshing or the simulation settings?
For the latter one, better ask the appropriate forums like CFX or Fluent.
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Old   July 31, 2024, 10:59
Default Bad Quality of meshing after inflation.
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After adding inflation, the quality of the mesh drastically drops, specially in inflation layers. I have calculated boundary layer(2.68mm) using empirical formula for turbulent flow. Using Y plus calculator, i have calculated the first layer thickness(9.1e-3mm). Then I have calculated the growth rate(1.2) and number of layers(22). what is the reason for bad quality mesh in inflation layer. I have used multizone to generate mesh for the cylindrical part of chamber.


Moreover, the quality of mesh isn't improving in the areas around nozzle, I have applied edge sizing etc.
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Old   July 31, 2024, 11:04
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Mostly the bad inflation is due to geometry or mesh settings. But what the problem is exactly, is impossible to tell without more information.
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Old   July 31, 2024, 14:40
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I have attached my geometry pictures. i have sliced the cylindrical portion in three sections. applied inflation and multizone meshing. the tangential oxidizers have tetra meshing at the junction and sweep meshing behind. The axial inlets have sweep meshing. Outlet also has multizone meshing
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Old   August 1, 2024, 04:14
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I would make a tull tet-prism mesh in a single volume. Then the mesh will be continous.
Now you have a lot of volumes with hex mesh from multizone, which is discontinuous. This is the real problem.

Quality is low at the wall where the elements are thin but very wide. There is nothing you can do about this. This is because you have inflation. Better get used to this.

Will you use fluent? Then why not use fluent meshing with a polyhedra mesh?
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Old   August 1, 2024, 15:28
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Thankyou so much for your detailed reply. I am new in fluent workspace. Initially I generated a tet mesh for full volume, however when i cut the midsection, the quality of elements was very bad. That's why I sliced my geometry and made Hex mesh. which has given me better results but no perfect results. Isn't Hex mesh better for covergence than tet mesh?


I am unsure as how to generate a polyhedral mesh, because in meshing method, it is not giving me option for a poly mesh.
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Old   August 1, 2024, 15:49
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Yes, hex mesh is better, but real geometries usually are not square. So, you need complex blocking structures to make a nice hexmesh.
Hex mesh results in better convergence and better results. But this is only valid for flow that is in line with the mesh. If your flow has swirl, or similar, then the advantages above polyhedra are much less.

In which software package do you now make your mesh? In the Workbench mesher? If so, you should switch to the fluent mesher. There you have access to polyhedra meshes, which is better for fluent. Fluent provived inaccurate results ith Tetrahedral elements.
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Old   August 1, 2024, 16:25
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Thankyou. I am using Fluent mesher. I will convert my meshing to poly and try running my model again.
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