[manupanand]

I am currently doing an incompressible pipe flow simulation with an extended domain at the inlet. I am attaching the simulation boundary condition etc. in figure.

My question is why my simulation has a low pressure than the inlet given property, I had given 101325pa at inlet , operating pressure 0Pa.

[yogesh03y]

Pipe flow will cause a pressure loss. Look up the Bernoulli's equation, Darcy-Weisbach equation and the Goldstein equation to understand it better. A negative pressure only means that the pressure is lower than the operating pressure. You have a really high mass flow rate at inlet. So pressure loss would be high as well.



A better way to define your BC would be to give the operating pressure as 101325 Pa and define a gauge pressure value at outlet, along with the mass flow rate inlet.