Emitter - Emitter

A grid fluid emitter always needs an object applied to be able to generate particles. The following settings are used to establish this connection and define the emitter’s mode of creating particles.

Object

This setting defines the object used for creating the particles. You can attach a new object at any time, but it is not possible to bind more than one object to an emitter. If you want to use more objects you have to add the appropriate number of emitters. We recommend removing the attached object from the "Relationship Editor", because the emitter object is not meant to interact with other nodes. In case you forgot to disconnect the emitter object, RealFlow will not consider it for the simulation anyway, but you will receive a warning in the “Messages” window. The attached object can have any shape and it is also possible to use imported objects.

Stream

By default, particles are created inside the volume of the attached object and then released. With this parameter it is possible to switch on a continuous particle stream, similar to RealFlow’s standard emitters. To make the emitter create particles with “Stream” turned on, “Initial speed” can even be 0.0. In such a case, the particles’ velocity is a result of the scene’s daemon forces.

Initial velocity

With “None”, the fluid's initial velocity is 0. With "Constant" the "@ speed" parameter is unlocked so you can type the initial speed of the fluid. The direction will be represented by the emitter's arrow in the viewport. With “Inherit” it uses the velocity of the attached emitter object – this is

interesting for animated emitter objects. With both "Constant" and "Inherit" the parameters to randomize the initial velocity will become accessible.

@ speed

Here you can adjust the particles' velocity at emission time in metres per second [m/s]. This parameter is only accessible when “Initial velocity” is set to “Constant”.

@ angle variation

This parameter is used to create more randomness and is measured in degrees [deg]. This parameter is only available with “Initial velocity” set to “Constant” or “Inherit”.

If you are interested in the technical background please continue reading: When the particles leave the emitter they have an initial velocity vector. When you define an angle variation, an angle is created around this vector, so it forms a so-called solid angle which looks like a cone. The final, randomized velocity vector will be inside this conical volume. 

@ speed variation

The particles' initial speed can also be modified to avoid a uniform look and add more randomness. The variation is given in metres per second [m/s] and will be combined with the value from “@ speed” or the attached object's inherited velocity. This parameter is only available with “Initial velocity” set to “Constant” or “Inherit”.

Surface particle sampling

Here you can adjust the number of particles per cell for the fluid's surface The total number of particles per cell is calculated with the following formula:

Number of particles per cell = Surface particle sampling 3

Surface bandwidth

Within the adjusted bandwidth (given in metres), the “Surface particle sampling” value will be applied to the particles. Below this distance, the “Core particle sampling” parameter is used. "Surface bandwidth" can be seen as the surface's "thickness".

Core particle sampling

Analogue to “Surface particle sampling” the main fluid body can be adjusted as well. With this parameter you determine the number of particles of a cell in the fluid's core are. The formula is exactly the same as above:

Number of particles per cell = Core particle sampling 3

Jittering

RealFlow spreads the particles of the emitter equally over the entire grid, respectively over the attached object’s volume. This results in a regular pattern and in some cases to slightly uniform simulations. To avoid this, it is possible to apply a random value to displace the particles from their original positions. The value determines the maximum distance from the original position without colliding with a neighbour particle. You can choose from values between 0 and 1 and, of course, “Jittering” leads to completely different simulations.

@ seed

This value is connected to “Jittering” and produces a random number for initializing the particles’ displacement.