Turbulence

The Turbulence node provides three methods of adding forces to the flow velocity that create swirlier motion and more fine detail.

Parameters

Perturbation

Perturbation adds random fine detail to the flow velocity.

Strength

Specifies strength of the perturbation force.

Seed

A seed value for the underlying random numbers. Different values will cause slightly different patterns to be generated.

Mask Channel/Region/Threshold

See Masking.

Vorticity

Vorticity amplifies existing vorticies (swirly motion patterns) in the flow velocity. This also helps to keep the vorticies alive longer.

Strength

Specifies strength of the vorticity amplification.

Mask Channel/Region/Threshold

See Masking.

Swirls

Add random swirls to the flow velocity.

Strength

Specifies the strength of the force that creates the swirls.

Scale

Specifies the size of the swirls.

Fluctuation

Specifies the rate of change of the underlying noise field.

Octaves

To generate swirls of different sizes, additional octaves can be used. Each additional octave will create swirls half the size of the previous octave. For example, if Scale = 1 and Octaves = 3, the scale of the smallest octave will be 0.25.

Note that the smallest octaves should still be larger than the voxel size for best results.

Roughness

Specifies the relative strength of smaller octaves. For example, when two octaves are used and Roughness = 0.5, then the 2nd octave has half the strength of the first once.

Seed

A seed value for the underlying random numbers. Different values will cause slightly different patterns to be generated.

Mask Channel/Region/Threshold

See Masking.

Masking

All three turbulence operators can optionally be controlled using a Mask Channel. This allows to restrict the Perturbation, Vorticity and/ Swirls to a region controlled by the selected channel. The temperature channel is usually a good channel to control the turbulence operators.

The Mask Region parameter selects whether turbulence will be added inside or outside the mask channel. Adding turbulence outside the mask channel, will effectively stir up the 'air' before the cloud reaches it. OTOH, when adding turbulence inside, the region of the cloud itself will be stirred up. The visual difference between the two modes is best observed by experimentation.

The Mask Threshold parameter allows to fine-tune the size of the region where turbulence is added. Using values larger than zero causes the inside region to become smaller and the outside region to become larger.