When a particle comes in contact with a wall, at time tc, the following options are available for what happens as a result of the particle-wall interaction.
where θ is the polar angle and
φ is the azimuthal angle. For both diffuse and isotropic scattering, the azimuthal angle is uniformly distributed in the interval [0, 2
π].
For diffuse scattering, the probability distribution function of the polar angle follows the cosine law, which states (Ref. 2) that the flux
dn of reflected particles within a differential solid angle
dω is proportional to the cosine of the polar angle,
Again defining a uniform random number Γ between 0 and 1, the polar angle is now
where Γ is uniformly distributed within the given interval.
The particle has probability γ to be reflected specularly, as if using the
Bounce condition. Otherwise the particle is reflected diffusely, as if using the
Diffuse scattering condition.
where vp (SI unit: m/s) is the user-defined velocity vector. The velocity can be specified either in Cartesian coordinates or in the normal-tangent coordinate system.
At the inlet the number of particles, particle position, initial velocity, and the number of releases is specified. An Inlet node can contribute with a
Wall or
Outlet node, so it is possible to specify a behavior for particles that return to the inlet at a later time.
At a boundary with the Thermal Reemission feature, particles are reflected into the modeling domain as if they were adsorbed at the wall and reemitted with the wall temperature.
The 3D form of f(W) is used in 3D models and in 2D models where the
Include out-of-plane degrees of freedom check box has been selected.
The values of W for 2D and 3D are gamma(1.5,1) and gamma(2,1) distributed random variables, respectively. The generators used to sample values of
W are (
Ref. 3)
Where N is a normally distributed random number with zero mean and unit variance, and the
Ui are uncorrelated uniformly distributed random numbers between 0 and 1.