Gas seems to flow backward?

I am trying to simulate H2 flows through a pipeline.

The simulation completes, but the gas seems to flow backward from inlet rather toward the outlet! I did try to switch the inlet and outlet face when selecting the boundary condition and rerun (Run 5 and 6), but the result is the same. The pressure of inlet is bigger than outlet. See the simulation below (Link imgur if your browser somehow does not support viewing)

Why is it the case? My project is at SimScale

Dear @yapabox589, to answer your question:

  1. The pressure postprocessing might bias you to assess the direction of flow. It is better to use velocity-vector postprocessing.
  2. You are using pressure-based inlets and outlets using a total pressure definition. According to this link, the definition of total pressure is:
    , therefore, a higher pressure would mean less velocity. As your inlet has a larger total pressure value than the outlet, the flow is being introduced from the outlet (which has a smaller total pressure value and thus a velocity magnitude greater than zero). For your case configuration, the inlet condition is being used as the initial condition and as the flow progresses towards it, the total pressure value decreases.

B.C’s can be tricky, this is why they must be studied to the utmost detail before running the case.

I hope this helps,