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envfluids / py2d

Python 2D Navier-Stokes solver
MIT License
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Definition of Delta #44

Open rmojgani opened 8 months ago

rmojgani commented 8 months ago

https://github.com/envfluids/py2d/blob/d2ab97207528519edec1feec8ee9d325b5ad036a/py2d/Py2D_solver.py#L115

Checking @gyf135 code,

Definition of $\Delta$ here seems to be wrong

It should be 

    Delta = L / NX

or for 2DHIT case to

    Delta = 2 * np.pi / NX

to match

https://github.com/envfluids/2D-DDP/blob/0542ca9dfeed3948b452d1307b85fddad6e82c25/physics-based%20codes/SMAG/F2DHIT_DSMAG.py#L80

@jakharkaran can you confirm this and it's downstream effects?

jakharkaran commented 8 months ago

The Delta is usually proportional to the grid size, L/NX. I have been using Delta = twice the grid size (FGR=2, Filter width to grid size ratio). Pavel's paper analyzes FGR in Appendix B1 for decaying turbulence. They use FGR=\sqrt(6) https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023MS003771

I plan to do a similar analysis for py2d at some point, and we can find an optimum FGR for our system. For now, you can consistently use the same FGR across all your runs.