Page History

Scale is crucial for the behavior of any simulation. The real-world size of the Simulator in units is important for the simulation dynamics. Large-scale simulations appear to move more slowly, while mid-to-small scale simulations have lots of vigorous movement. When you create your Simulator, you must check the Grid rollout where the real-world extents of the Simulator are shown. If the size of the Simulator in the scene cannot be changed, you can cheat the solver into working as if the scale is larger or smaller by changing the Scene Scale option in the Grid rollout.

The Phoenix FD solver is not affected by how you choose to view the Display Unit Scale - it is just a matter of convenience.

Go to Customize → Units Setup and set Display Unit Scale to Metric Centimeters.

Also, set the System Units such that 1 Unit equals 1 Centimeter.

Since the simulated balloon geometry has no thickness, we can't use it as-is in the Phoenix FD simulation.

Apply a Shell modifier to the balloon and set Outer Amount to 0.1 cm.

This value can be modified depending on the size of the balloon object and the resolution of the Phoenix FD simulation.

Create a LiquidSrc helper from the Helperstab of the Command Panel of Phoenix FD.

Add the Geosphere as an emitter with the Add button.

Create a Liquid Simulator from the Phoenix FD toolbar Toolbar or the Phoenix FD menu of the Create panel.

Adjust its size so that it encompasses the balloon geometry and try to align it to the camera.

The Cell size parameter does not have to be excessively small during the RnD stage - you can set it to 0.3 cm.
Enable Adaptive Grid and configure the range of Maximum Expansion for X, Y and Z as shown in the picture.

Notice that the back of the balloon is partially outside of the simulation grid. This way we can save some resources and reduce the required memory for the simulation. The back side is pretty much irrelevant considering the camera angle.

Set Gravity to a low value (0.05) so the liquid is almost weightless.

Set the Steps per Frame parameter to 2.

Low values will give you a 'noisy' result which is ideal for explosions. High values (10 or more) tend to smooth out the movement of the liquid. A value of 2 gives a good result, so that's what is used in this tutorial. You can increase it if needed.

The Time Scale is set to 0.7 to slow things down a bit.

Set Surface Tension to 0.05 (as a comparison, the surface tension of water is 0.05 ~0.10).

Wetting is enabled, with the Consumed Liquid option set to 0.1, and the Drying Time to 0.01 seconds.

Wetmap particles are born on the surface of objects which come into contact with the liquid. A Wetmap particle group is created which can be used at render time to drive the options of a material using a Phoenix FD Particle Texture.

Wetmap particles also allow the liquid to stick to the surface of objects when Surface Tension and/or Viscosity is above 0.

On the PhoenixFD Phoenix Properties of the balloon geometry, set the Motion Velocity Effect parameter to -1.0.
When the rubber pieces move away from the fluid, the velocities sourced into the simulation point towards the center of the liquid, as opposed to the previous setup, where the balloon geometry is dragging the liquid outward. This causes pressure build-up and random splashing to occur.