[FireTower]

Good morning everyone,

Currently, I'm trying to prove the conservation of momentum in a waterjet inlet. In order to do so, I defined a control volume with both solid and fluid walls. To find the force contributions on the solid walls the wall shear stress and pressure can be used. However, there is also a shear contribution on my fluid wall boundaries (probably quite low). How can I define the contribution of turbulent & viscous shear on those fluid walls because the function wall shear stress is not possible on those derived parts?

In the image, the control volume "box" can be seen just below the waterjet inlet. With the tunnel inlet on the right and on the left both tunnel and duct outlet.

I hope somebody can help me,

Thank you in advance!