Contact line instability and thickness profiles of spreading films

J. DIEZ; J. GOMBA; A. G. GONZÁLEZ; R. GRATTON; L. KONDIC

Austin, EE.UU

Conferencia; Division of Fluid Dynamics 55th Annual Meeting, APS; 2002

We study experimentally and theoretically the vertical spreading of fixed volumes of silicon oil films (\nu =10St), which exhibit a contact line instability by developing a finger-like structure. The initial condition is given by a thin horizontal filament of typical diameter 0.4mm. Two diagnostic methods are used. One consists of a Schlieren technique producing bright and dark zones in correspondence to the gradient of the film thickness. The other technique yields an analog representation of the thickness gradient along the spreading direction at places where its transverse components are very small, as it occurs along the fingers or at the troughs. By means of these techniques we determine very precisely the length and distance of the fingers as a function of time, as well as the dynamic contact angle at the tips, and the maximum thickness at the tips and troughs. These results are then compared with fully nonlinear numerical simulations. We show that the approach that assumes constant thickness of the film far behind the contact line has only a very limited range of validity, and we proceed to develop an extended model to account for the details of the instability development.