# Air-blast-atomizer azimuthal angle reference system and mass flow rate

ANSYS Fluent 18.2. I have to simulate a spray through a semicircular inlet (whose normal vector is axis -X) with a given flow rate of 1 kg/s **on the whole circle** (it's a symmetry-plane system). I guess I have to set *start azimuthal angle* to 0° but I don't know whether the *stop azimuthal angle* would be 180° or -180°. In other words, I don't know what is the reference system for rotation used by Fluent. The inlet half which will be crossed by the spray is the superior one.

Furthermore, which mass flow rate do I have to put in *injection* point properties? 1 kg/s or halved?

## Comments

If you simulate half of the atomizer with a symmetric plane, then use half of the total mass flow rate.

Please clarify your first question with some geometry plots.

Thank you for your reply. Yes, it a symmetric-plane problem. Now I'm wondering whether I have to specify an azimuthal angle less than 360° or it is accounted automatically given the symmetry. As you can see, the spray is directed along the -X axis

If you only have half of the domain then any particles that are created outside of the mesh won't be processed. So try 0-180 and 180-360 and see which puts particles into the domain.

Ok, thank you. Which flow rate should I have to choose if I set 0-180 (or 180-360)? 1 kg/s or half?

The flow rate is the one of 360 degrees. Fluent will use for the effective mass flow through the nozzle your input divided by the azimuthal angle difference multiplied with 2*PI. Regarding the angles: keep in mind that we rely on right hand rule and that counterclockwise is always positive. Just stick to rwoolhou suggestion to get the right range.