Contact Angle

The default wetting behavior on walls for the TARTAKOVSKY2016_F1 surface tension model is neutral with a static contact angle of 90 degrees. Enabling the contact angle parameter allows simulation of different wetting behaviors in single phase flows (the only type of flows the model is currently recommended for).

Contact angle is a single value prescribed as a solid surface/boundary property. This can be set via the parameter contact_angle in the phases subsection of the .cfg file for any WALL or MOVINGWALL phase and will be ignored for fluid phases. It is measured as the angle ( ${\theta }_c$ ) between solid and fluid surface with respect to the (resolved) fluid phase.

Figure 1.

An angle of less than 90 degrees develops hydrophilic behavior and an angle greater than 90 degrees develops hydrophobic behavior. Figure 2 illustrates this with a droplet on a flat surface with contact angles of 30, 60, 90 and 120 degrees.

Figure 2.

Figure 3 contains isometric, plan, and elevation views of three droplets with equal volume. From left to right the droplets are assigned contact angles of 30, 90 and 120 degrees. This illustrates that contact angle affects the particle spread and distance from the wall.

Figure 3.

Wetting behavior is highly sensitive to numerical (particles aligned on a Cartesian grid) and experimental (surface type and cleanness) setups. This parameter should not be interpreted as a precise parameter down to a single degree, but rather an estimate of the wetting behavior in general (wetting/non-wetting to certain degrees).