The effect of partial wetting by film liquid describes the behaviour such as rivulets, dry patches, and film rupture on a wall surface and is modeled using the partial wetting model described by Meredith [435].

The surface force due to film surface tension in Equation 17–2 is given as:

(17–29)

where is the film surface tension, is an empirical parameter to account for discrepancies between the model and observed film behaviour, and represents the film wet area fraction.

The film contact angle is sampled randomly from a Gaussian distribution over the film wall characterized by the mean contact angle and its standard deviation (where is a percentage fraction factor). The contact angle can also be specified using user-defined functions (UDFs).

The film wet area fraction is given as:

(17–30)

where is the critical film thickness. If the thickness of the liquid film is above the critical value , the wall is considered to be wet. If the film thickness is below this value, the wall is considered to be dry. In the Ansys Fluent Eulerian Wall Film (EWF) model, takes the value of 1e-10m.