in rare cases, NSCBC outflow produces unphysically high velocities #532
Labels
bug
Something isn't working
Comments
BenWibking
changed the title
BenWibking
changed the title
7 tasks
github-merge-queue bot
pushed a commit
that referenced
this issue
Apr 8, 2024
### Description This adds simplified subsonic inflow and outflow boundary conditions. For outflows, it specifies the pressure at the outflow and extrapolates the other primitive variables (while turning into a reflecting boundary if the normal velocity is inflowing). For inflows, it specifies the velocity components, the temperature, and the passive scalars, while extrapolating the density. Unlike the naive boundary conditions, these boundary conditions are well-posed, since they specify the correct number of quantities required for the steady-state solution to be unique. The amplitude of reflected waves is greater than for the NSCBC boundary conditions, but these boundary conditions are much more stable in the presence of supersonic turbulent flow near the boundary. ### Related issues Workaround for #532. ### Checklist _Before this pull request can be reviewed, all of these tasks should be completed. Denote completed tasks with an `x` inside the square brackets `[ ]` in the Markdown source below:_ - [x] I have added a description (see above). - [x] I have added a link to any related issues see (see above). - [x] I have read the [Contributing Guide](https://github.com/quokka-astro/quokka/blob/development/CONTRIBUTING.md). - [ ] I have added tests for any new physics that this PR adds to the code. - [x] I have tested this PR on my local computer and all tests pass. - [x] I have manually triggered the GPU tests with the magic comment `/azp run`. - [ ] I have requested a reviewer for this PR.
|
@BenWibking is this now resolved by #598 ? |
Yes, in the sense that the simple version of the boundary conditions added in #598 doesn't have this problem. No, in the sense that the real NSCBC still has this problem. |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Describe the bug
In very rare circumstances, the NSCBC outflow boundary conditions can produce states in isolated cells at the boundary that have unphysically high velocities. An ad hoc (but partially effective) workaround is to revert to zero-gradient extrapolation when the velocity in the ghost cells would otherwise be extremely large (for example, > 1e10 cm/s).
To Reproduce
This was observed after about 40,000 timesteps while running the updated shock-cloud problem at 1024x256x256 resolution with no refinement.
Additional context
A similar failure mode (but with negative densities instead) was seen in #472.
The text was updated successfully, but these errors were encountered: