How to calculate what a fluid's Inflow Velocity should be?

I copied the rotation values from my inflow object, thinking that would point my inflow in the correct direction. It did not.

Next I tried just putting in a value for Z, hoping it would use the Local Z coordinate of my inflow object. It did not.

What is the correct way to determine what the inflow XYZ values should be? (Assuming you have an object pointing in the right direction already as a basis to calculate from)


The X Y and Z inflow values are the speed in each world axis. the inflow direction will the combination of the three speed directions.

To have the inflow going in some arbitray angle you could set the inflow to Z for example, parent the inflow to an empty and rotate the empty to match your target inflow direction. (not tested this but assume it will work). then you don’t need to worry about mix and matching different axis inflow speeds

Thank you for the suggestion, however this did not work. The Inflow Velocity values are world coordinates and they ignore all parent-child relationships, object local rotation, and well… anything else except for world coordinates. Not a very user-friendly schema.
But complaining about it will do no good, so at this point I’m trying to figure out how to do the math to work around it.

In the Inflow settings there is an option to use Local Coordinates. I’m not able to test at the moment but you could try testing that

Yes! Thank you, I just tried this and it works perfectly.
Not obvious at a glance, but once you know to check that option it’s easy as pie.