I want to simulate the 3D flow in channel I used the inlet velocity and pressure outlet as a inlet and outlet B.C and specifying constant value for velocity at the inlet But after calcuations when I calculate the velocity at the outlet by surface integral I found the value of velocity in the outlet differ from its value at the inlet.Why this happened ? and is the momentume is not conserved here? Thank you

you have to check the mass flow to check the conservation. velocity will differ because of low velocity near the wall.

I know that the velocity is increase untile reaching the fully develop region but I speaking about the mean velocity which must be remain constant as I know from the fluid mechanics.But in my case it changed from inlet to outlet my question is whay this happened

Thank you alot

hHve you defined the material as compressible (ideal gas)?. Whether the area inlet and outlet are same?

have you defined the material as compressible (ideal gas)?. Whether the area inlet and outlet are same?