Use the Wall node to determine what happens to the particles when contact with a wall is made. The
Accumulator (Boundary) subnode is available from the context menu (right-click the parent node) or from the
Physics toolbar,
Attributes menu. If
Newtonian,
Newtonian, first order,
Lagrangian, or
Hamiltonian is selected from the
Formulation list in the physics interface
Particle Release and Propagation section, the
Secondary Emission subnode is also available.
The Wall node can be applied to interior or exterior boundaries, but the instance of this node that is created by default only applies to exterior boundaries.
If Massless is selected from the
Formulation list in the physics interface
Particle Release and Propagation section, only the
Freeze (default),
Stick, and
Disappear conditions are available.
Enter values for the Reflected particle velocity vp (SI unit: m/s) either in Cartesian coordinates (x, y, z) (the default) or select the
Specify tangential and normal velocity components check box to enter coordinates in the tangent-normal coordinate system (t1, t2, n). In this case the normal direction is selected so that an incident particle is reflected back into the domain it previously occupied if the specified normal velocity component is positive. The tangential directions are oriented so that they form a right-handed coordinate system, together with the normal direction. As a result, the tangential and normal directions may point in the opposite direction of the corresponding vectors defined for the geometry (for example,
root.nx) and for the physics interface (for example,
pt.nx).
Select a Primary particle condition:
None (the default),
Probability, or
Expression. When the default,
None, is kept, it means that the
Wall condition is always respected by the incident particles.
If Probability is selected, the
Wall condition is applied with a certain probability. Enter a value for the
Probability γ (dimensionless) of the particle behaving according to the
Wall condition. Otherwise the particle behaves according to the
Otherwise setting.
If Expression is selected, the
Evaluation expression e (dimensionless) is evaluated whenever the particle strikes the wall. The default value is 1. If the
Evaluation expression is nonzero, the particle behaves according to the
Wall condition, otherwise the particle behaves according to the
Otherwise setting.
The options available for the Otherwise setting are the same as for the
Wall Condition, except that
Mixed diffuse and specular reflection and
General reflection are not available. The
Otherwise setting can be used to make particles interact with a wall differently when a certain condition is satisfied. For example, to specify that particles with a diameter greater than
1 μm stick to an interior boundary, and the rest pass through:
Select the Assign new value to auxiliary variable check box or boxes based on the number of auxiliary variables in the model. Then enter the new value or expression in the field. For example, if there is an auxiliary variable,
psi, then enter a value for
psinew in the field. So, to increment the value of
psi by one when a particle touches or crosses a boundary, enter
psi+1 in the text field for
psinew.
If the Primary particle condition is set to
Probability, or if the
Diffuse scattering or
Isotropic scattering wall condition is used, then the
Wall feature generates random numbers. If, in addition, the
Arguments for random number generation setting is
User defined, the
Advanced Settings section is available. Enter the
Additional input argument to random number generator. The default value is 1.