hi everyone,

I want to set a mass flow rate for an outlet boundary. Idealy, i want the flow field to adjust itself around curves and so on and exit the boundary with a non-uniform velocity profile. My question is this: what type of mass flow rate should i choose for the outlet boundary condition in cfx - assuming i don't know the velocity profile at the outlet?

Hi Harun,

The default mass flow outlet will do this. The specific option is "Scale Mass Flows". This allows the local mass flow rate to scale naturally across the boundary.

Alternatively, you can specify a pressure profile at your outlet using the "Shift Pressure" option. This will shift your pressure profile up or down to acheive the desired mass flow rate. Local velocities will still vary in this case. The pressure can also be applied as a circumferentially averaged profile, allowing the pressure to float circumferentially but maintaining the circumferential average.

The last option is constant flux. This will force a uniform mass flux through the face. This option is useful for avaoiding convergence problems at things like bleeds, particularly if the boundary condition is parallel to the mean flow, but is generally undesirable if your outlet in very close to a region of interest, since the effect on velocity is unphysical.

Regards, Robin