Use channel fields to modify the values of voxel or particle channels in a fluid simulation, such as the density of the liquid or foam.
You can limit the effect to a specific volume using closed polygon meshes in the scene, or an implicit shape. This is useful, for example, to add turmoil to an otherwise static body of water. For example, to simulate a heated pot of water you could use a Channel Field object to decrease the density in the centre of the fluid so when simulated it resembles a roiling boil.
Note that the final values of a channel might not always correspond exactly to the settings of a channel field. For example, you might use a channel field to clamp the vorticity channel of a liquid, but then new vorticity values will be calculated after the velocities are updated by the simulation. The clamping will prevent the vorticity values from accumulating too high, but some values may nevertheless be higher than the maximum set by the channel field.