Coating Insights
Fingering in Liquid Films
Fingering of liquid sheets. 0° contact
angle on left and 70° contact
angle on right.
In FLOW-3D dynamic contact lines are modeled directly without the need to specify dynamic contact angles or the location of the contact lines. This is accomplished by using a numerical model that includes all the dynamic forces affecting fluid in small control volumes. Static contact angles are used to characterize liquid-solid adhesive forces. An application of the power of this approach is given by the fingering observed in liquid films flowing down an inclined surface. Experimental observations show that two distinct patterns of fingering occur. One pattern, corresponding to small static contact angles (i.e., highly wetting conditions), exhibits wedge shaped fingers whose top and bottom limits both move downward. The second pattern, corresponding to large static contact angles (i.e., poorly wetting conditions), is characterized by long fingers of nearly uniform width whose top most limits are not moving downward. In the accompanying figure we compare the results of two FLOW-3D simulations with experiments (Silvi, N. and Dussan V, E.B., On the rewetting of an inclined solid surface by a liquid, Phys. Fluids, 28, p.5, 1985).The simulations used the assumption of depth-averaged flow, which is justified because of the thinness of the liquid films. The only difference between the two simulations is the value of the static contact angle (The computational results do an excellent job of reproducing all the essential features of the observed flows).
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