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sod's test by lax-friedrichs method

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Old   December 15, 2018, 07:14
Default sod's test by lax-friedrichs method
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hi everyone!
I've been solving Sod's Shock Tube Problem with Lax-Friedrichs method on C++. I use this link as the main one. But I face the problem with defining entropy. I found
  • density,
  • velocity,
  • pressure,
  • Mach number,
  • speed of sound;
but entropy fails. Can anyone help me with it?


P.S. I attached the archive with code and graphs
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File Type: zip sod laxfriedrichs.zip (152.5 KB, 2 views)
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Old   December 20, 2018, 13:40
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Dear mend4x,
Entropy in general is a value, which is calculated via integral relation. This means, you have to know the reference state to compare your solution. Nevertheless you can compare the difference between two neighboor cells or you can shift your solution to the correct level.
You should also check if the reference solution uses Entropy per mass or Entropy per volume.

If your calculation variables match the reference, then the problem is only a post-processing issue.
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euler equation, lax-friedrichs, riemman, sod shock tube

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