Determining fluid speed is important to ensure proper blending between slices, when distributing up res fluids. To begin, you should look at the maximum velocity across the distribution boundary. If you only have vertical distribution cuts, gravity doesn’t matter.

One approach is to add the following nodes your low res DOP sim:

• Gas Match Field to create two vector fields called maxspeed and minspeed of the same size and sampling as vel.

• Gas Reduce of vel to maxspeed with Maximum, and of vel to minspeed with Minimum.

Next, run the simulation forward to where you see the most action across the future distribution boundaries, and extract those two fields. They will have constant value everywhere, so you can sample them using a volumesample() to get what the max/min speed is. You can use the maximum speed for distribution.

Another option is to scatter a bunch of representative points. Then use a VOP SOP to copy the velocity onto those points. You can then use an Attribute Promote to promote the point velocity to a detail velocity with the proper max/min, where you can read the results in the spreadsheet.