Differences between steady and unsteady CFD calculation
Alex POIRIER
Hi everybody,
I ran a steady state + transient CFD simulation on a centrifugal compressor (with a k-omega SST model) and when post-processing the results and comparing the stationary part to the unsteady part of the calculation I have significantly different results. Indeed, the unsteady part shows a higher mass flow rate. This seems to be due to a higher flow speed and a different flow angle, noticeable directly at the inlet of the rotor. On the picture attached you see these differences (on the left: unsteady part; on the right: steady state part). Is it possible that this difference in flow rate could be explained by the fact that the dynamic mesh in the unsteady part could aspire the flow in the rotor and thus change the angle and speed of this one? And maybe this effect could have been lower if I would have set a lower CFL (kept for now to 20 in my case)?
If you have any ideas about this phenomenon that would be very helpful.
Thanks and have a great day,
Alex