Proposed Changes

I discovered that the Aachen regression test was actually on its way to divergence. I think this explains why the regression test was behaving inconsistently, although I'm not sure about what caused this problem.

I made a new mesh, introduced wall functions as suggested by @joshkellyjak, and switched to second order directly.
The convergence history is good. See the attached convergence histories obtained with JST starting from scratch with outlet pressure ramp.

I have finally updated the restart files accordingly.

Related Work

I think these small changes could fix the issues encountered in the past with this test case.

PR Checklist

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