Thanks for you answer,
In reality there will be no flow for t<0. When t=0, the flow begins from 210 bar source and exiting the geometry from two outlet ports with 0 bar.
In my model, the first narrow point restricts flow for t<0. When t=0, the motion begins and the narrow part gets bigger and the flow proceeds towards to the both exit ports. When the motion is done, the second narrow part is created on the left side and restricts flow to go out from the left outlet port.