As usual in SPH
1 implementations, viscosity is rather an
inter-particles pressure than a bulk pressure. It was shown that the use of
Equation 1 and
Equation 2 generates a
substantial amount of entropy in regions of strong shear even if there is no
compression.
(1)
with
(2)
Where,
(resp.
) indicates the position of particle I (resp.
) and
(resp
) is the sound speed at location
(resp.
), and
and
are constants. This leads us to introduce
Equation 3 and
Equation 4.
2 The artificial viscosity is decreased in
regions where vorticity is high with respect to velocity divergence.
(3)
with
(4)
Default values for
and
are respectively set to 2 and 1.