Graphics Reference
In-Depth Information
Viscosity
Every fluid has a particular
viscosity
, which determines the speed and ease with which it flows. Viscosity is
a measure of the fluid's resistance to the forces that deform it. Fluids with high viscosity flow slowly and are
perceived as thick, whereas low-viscosity fluids, such as water, are thin. For example, think of the difference
between the way that fluids such as water, motor oil, honey, and magma flow—this mainly has to do with their
viscosities.
The value used in Blender is known more precisely as the
kinematic viscosity
. In Blender's fluid simulator,
the fluid's viscosity can be entered by hand or by using a preset value. Preset viscosity values are also available
in the drop-down menu in the Domain World panel. The preset viscosities include Honey, Oil, and Water. The
default is Water.
If you select Manual, you can enter a Base viscosity value and an Exponent by hand, as shown in
Figure
7-13
.
The default is Base 1 and Exponent 6, which represents the value 1 × 10
-6
(the value for water, as shown
in
Table 7-1
). Remember, the viscosity setting is only one of several parameters that affect the
appearance
of
viscosity in the simulation. Several other factors, notably the resolution of the simulation, also have a great
impact on how the fluid looks. The Manual setting can come in handy if you want to simulate a fluid with a
significantly different viscosity than the presets, or if you are trying to fake the effect of a fluid simulation that
occupies more than a 10-meter area, because a larger area can “thin” the fluid out. Coupled with particle-based
spray, using the Manual setting can enhance the effect of larger-scale simulations.
Figure 7-13
Manual viscosity settings
Some fluids and their kinematic viscosities are listed in
Table 7-1
.
Table 7-1:
Kinematic viscosity of selected fluids
Fluid Kinematic Viscosity
Water (20°) 1 × 10
-6
(0.000001)
Oil SAE 50 5 × 10
-5
(0.00005)
Honey (20°) 2 × 10
-3
(0.002)
Chocolate syrup 3 × 10
-3
(0.003)
