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
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 Re-Emission feature, particles are reflected into the modeling domain as if they were adsorbed at the wall and re-emitted 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.