A modification of a bellow flow project of @bhalterman
In order to get the simulation to run the inlet and outlet area were extended.
Also the inlet flow rate was ramped over 500 steps, and then left to converge for 500 more steps.
This was the first time I looked at a profile of a bellows flow. It is amazing how the separation caused by the geometry and induced turbulence squeezes the main flow! It seems not a significant change and yet it has profound effects on the results! Definitely one has to pay attention when using flex hoses with high velocity flows.