# Splitting & remerging flow simulation

Question asked by Nathan Reetz on Dec 21, 2020
Latest reply on Jan 4, 2021 by Sylvain Grondin

Hi everyone,

I am trying to run a flow simulation on a part that has a single flow inlet and outlet, but diverges flow through an orifice and a bypass and recombines them downstream. I originally had some good results a few weeks ago with this simulation but something must have happened where now I am getting unrealistic solutions. Here's the geometry being tested:

The annotations are for Volumetric flow rate at the inlet, outlet, orifice, and bypass. The boundary conditions are as follows:

Outlet Volume Flow: 5066 cm^3/min

Inlet Total Pressure: 4000 Pa (30 torr)

Goals:

PG Static Pressure @ point 1

PG Velocity @ point 1

PG Static Pressure @ point 2

PG Velocity @ point 2

Pressure Difference Equation (P1-P2)

Velocity Difference Equation (V1-V2)

See bottom of post for other general/fluid settings.

Problem/expected behavior:

When the simulation was working well (closely resembled experimental data) it had less flow through the orifice and more through the bypass, there was ~5x the pressure drop from point 1 to point 2, and the volume flow rates added up neatly (orifice + bypass = inlet = outlet).

References I used:

I used this youtube demonstration as a basis for the setup of the system: Solidworks CFD tutorial: Venturimeter CFD - YouTube . A venturi meter was the closest application video I could find to the type of splitting and merging flow in my system.

I have been racking my brain for 3 weeks about what went wrong and how to fix it so any and all help is greatly appreciated!

Other General/Fluid Settings: