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Mantaflow - liquid inflow initial velocity settings have no effect
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Description

System Information
Operating system: Windows 10 Home, Version 10.0.18363 Build 18363

Graphics card: ASUS R9 290X DirectCU II OC

Blender Version
Broken: V2.82 Beta, fc1f5bded46a, 2020-01-24, as found on the splash screen
Worked: could not get it work on previous versions either

In the attached file the object 'water_jet_inflow' 'Initial Velocity' settings seem to take no effect at all. I tried various combinations of settings and the result was either the same visual output or no output at all.
The objective was to generate a jet like stream as the disk moves to the right, as seen on the attached image by the red arrow path and the file. If I remove the animation of the disk then the particles just flow towards the bottom of the screen and see no velocity change. In the blend 2.82 manual I could only find the old fluid sim related information, nothing about the Mantaflow settings but I tried different combinations and nothing produced any change there.
Also, is the initial velocity x.y and z direction in m/s or what unit is it supposed to be because there is no mention in the popup info when hovering the settings?

Mantaflow Water Jet propulsion test.blend615 KBDownload

Related Objects

Event Timeline

Andrew Sprok (sprad001) created this task.Jan 27 2020, 1:10 AM
Richard Antalik (ISS) changed the task status from Needs Triage to Confirmed.Jan 27 2020, 6:13 PM
Richard Antalik (ISS) added a project: Nodes & Physics.
Richard Antalik (ISS) merged a task: T73425: when using liquids the inflow source has no way to control the rate of inflow .Jan 27 2020, 6:30 PM
Richard Antalik (ISS) added a subscriber: Unknown Object (User).
Sebastián Barschkis (sebbas) mentioned this in rB33317b464777: Fluid: Fixes for flow objects and initial velocities.Jan 29 2020, 7:23 PM
Sebastián Barschkis (sebbas) changed the task status from Confirmed to Needs Information from User.Feb 3 2020, 12:29 PM
Sebastián Barschkis (sebbas) added a subscriber: Sebastián Barschkis (sebbas).

Hi! Can you try to out the latest Blender build. I made some changes to initial velocities in 33317b464777

Also, when I looked at the file I found the following things that are important to keep in mind:

  • When emitting from a flat object, this object must have a face and a "Surface Emission" > 0.
  • When emitting from an object with volume, think twice about using the normal component in the "Initial Velocity" settings. In most cases the XYZ components are what you're looking for.
  • If your emitters produce a lot of fluid then make outflow objects even bigger.

For reference, here is how I changed the emitters from your scene:

Plane emitter:

Volume emitter:

Andrew Sprok (sprad001) added a comment.Feb 5 2020, 2:35 PM

Hi Sebbas,
Thanks for the tips. I tried them and worked.
Not sure what the Normal component does so I left that alone.
What I find difficult is to control the amount of fluid. If the emitter is smaller than 0.1x0.1x0.1 it stops emitting. The other thing is the amount of liquid is dependent on size of the object, the Resolutions Divisions, Time Scale, Liquid Particle Maximum and Initial Velocities. For example I do not know how I could simulate a water hose to have a continuous jet of water coming out of a 1cm orifice and creating a continuous water stream in a 10m x 2m x 2m domain.
I also observed that if I get a good water flow from an object, if I change the domain size to double or triple then every setting is out of place and have to find some combination that works again.
All this experimentation also led me to discover some fluid particle problems which I reported here T73552, if that is actually a problem and not related to some settings.

Aaron Carlisle (Blendify) closed this task as Resolved.Feb 14 2020, 10:26 PM
Aaron Carlisle (Blendify) claimed this task.