Learning Forum

[Parviz]

Hello everyone

I modeled one vertical suction pipe with a 10 cm diameter inside the bigger pipe in 3D format. The suction pump did not model. I got the properties of flow practically and water velocity at the end of the suction pipe stand 0.5 to 1.8 m/s. Therefore, the flow has turbulence conditions. Maximum Aspect Ratio = 8.3. The solver SST K-omega.

The important things are water velocity in the area from end of the bigger pipe to entrance suction pipe.

First boundaries condition " Inlet = velocity inlet, Outlet = Outflow" . Then I change them to "Inlet = Pressure inlet, Outlet = Velocity inlet with minus velocity magnitude. In both cases, the residuals did not convergences. I run it also with decreased under-relaxation factors but no success.

0.31- 3.png

[Rob]

Convergence can depend on several factors, mesh being one of them. Re the boundary conditions, velocity in/out and pressure is the best combination: do not use outflow as it has a number of limitations. Staff are not permitted to open attachments or down load files. Please repost the images and add some for velocity & mesh so we can see what's going on.

[Parviz]

Thank you Rob for your reply.
I attached the pictures again. I

[Rob]

OK. The best choice of boundary here depends on how the flow is when it reaches the surface. A suction velocity will assume a uniform value so may give convergence issues if the flow is very disturbed. You've also picked up an asymmetry in the flow, which is probably moving slightly with each iteration. It's probably not far off what would happen in reality as perfectly symmetrical flows almost never exist.
Check the flux balance and see how good that is.