Numerical oscillations in test case `Left_coronary_inlet_pressure_wave_outlet_coronary.in` when using smaller time step

Description

Description
When running the test case Left_coronary_inlet_pressure_wave_outlet_coronary.in, I observed numerical oscillations in the flow rate when using a smaller time step than the value used in the parameter file.

With dt = 1e-3, the flow rate exhibits noticeable numerical oscillations (visible in Paraview). Oscillations remain even if I postprocess myself the sim data, so Paraview is not the culprit.
With the default dt = 5e-3, no oscillations appear.

Questions

• Is this behaviour intended or expected for this test case?
• If it is expected, could you explain briefly why reducing dt may produce oscillations in this setup?

Reproduction

In particular, I:

1. Used the provided test case Left_coronary_inlet_pressure_wave_outlet_coronary.in.
2. Set the time step to dt = 1e-3 (the default was 5e-3).
3. Ran the simulation and evaluated the flow rate at a section of the LAD (see attached png).

Environment

• OS: Ubuntu 22.04
• Skyline solver
• commit: 66b31b4221b8dc9c04a767ed48e6a5367f63a499

Expected behavior

Using a smaller time step would normally improve stability or accuracy, so oscillations were not expected.

Additional context

No response

Code of Conduct

• I agree to follow this project's Code of Conduct and Contributing Guidelines

Start by rerunning Left_coronary_inlet_pressure_wave_outlet_coronary.in with dt=1e-3 and the default dt=5e-3, then compare the LAD flow rate independently of ParaView. Investigate the solver's time-stepping and coronary boundary-condition behavior for this case. Done means determining whether the oscillations are expected and documenting the cause, or identifying a reproducible solver defect.