Learning Forum

[Nathan Blackmore-Wells]

Hi,

A tiny bit of context: I'm running an open channel 2D Fluent simulation to try to find an outlet velocity profile to use as an inlet in a different case.

My inlet for the first case is a mass flow inlet of water, with a surface height 1m in a 2m channel with a small slope (0.0005). I want it to run such that there are no surface waves (Fr<1). I have this figured out and choose to run a mass flow inlet of 2100kg/s and get a flat, wave-free channel with a mass flow at outlet of almost, 2100kg/s. Happy days. So i export the velocity profile.

I then want to reuse this velocity profile in the same geometry with a pressure inlet specified by free surface height and velocity magnitude. When i put this v-prof into the v-mag box the mass flow i got is only around 1700kg/s and seems to change as the solution converges.

i need this mass flow rate to remain constant to control the simulation and avoid surface waves.

a) Why is the mass flow not constant if i have a profile for velocity and a set height that doesnt change between the two cases? Have i not set both the U and the A (=h) of the inlet (Q=UA)?

b) Why does this change during convergence?

 

I'd hugely appreciate any help or suggestions for alternate ways i can do this

 

-Nate

[Essence]

Hello,

When you try to export the velocity profile, check if the velocity profile is of magnitude or components. If components, then you need to apply the velocity profile in the components and not the magnitude.