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Need help with HELYX-OS Compressible Flow Simulation

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Old   February 13, 2014, 19:44
Exclamation Need help with HELYX-OS Compressible Flow Simulation
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Hello there,

I am very new to OpenFOAM which is the reason why I am using a GUI. Currently, I'm trying to simulate a wedge airfoil in a supersonic wind tunnel.

I want to ask several things :
  1. What is base mesh ? Is it a location where boundary conditions can be placed ?
  2. Actually the meshing went without any problem whatsoever. However, I am still unfamiliar with the boundary conditions. What kind of settings should I use for inlet and outlet if I have the data of inlet velocity and static P and T ?
Well, I guess that's it for now. Thanks to everyone at CFD Online.
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Old   February 13, 2014, 20:37
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Daniel P. Combest
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The Base Mesh
snappyHexMesh uses a cut-cell type approach in which
  1. a base mesh is create
  2. cells are refined near where a surface intersects with the base mesh
  3. a mesh is castellated i.e. the cells not involved in the simulation are removed
  4. the cells are cut and snapped to conform to the surface
  5. and then layers are added.
A smaller base mesh will ultimately create more cells in your mesh, but will allow for better approximations of your surfaces and could make higher quality cells for layer addition. All of this is governed by mesh quality criteria i.e. if adding a layer creates worse cells than they were layer is added. If all goes well you are left with a mesh. There are a few presentations/resources about the topic
Boundary Conditions
Now, on the boundary can refer to this presentation. You can also read through the OpenFOAM user's manual for some tips or read a really fantastic source on the subject Hrv Jasak's Thesis, one of the original developers of OpenFOAM. For the most part, you set inlet velocity to type patch with fixedValue and inlet pressure to zeroGradient; outlet pressure to 0 for incompressible flows or something like 1e5 for compressible flows and velocity to zeroGradient; inlet temperature if fixed value and zeroGradient outlet; and then there are many many many variations that are appropriate for stability, accuracy, and portraying real phenomena...accurately. For your case, you will want to look at some of the higher mach boundary conditions like superSonicFreeStream (for velocity inlets) and waveTransmissive (for your pressure outlet). For mapping experimental results directly...then you may need to look a bit more on the forum...I'm drawing a blank. I hope this gets you started.
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Old   February 16, 2014, 23:25
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Woah, so HELYX-OS is OpenFOAM afterall. Thanks for the info. I'll see if I can make it right. However, I'm still looking for a compressible flow tutorial if there's any.
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