Title: On moving contact line and contact angle during reflection of a solitary wave
Speaker: Yong-Sung Park, University of Dundee, UK
Time and place: Friday Nov 17th，14:40-15:40, 欧阳纯美楼316
In a set of wave flume experiments for a solitary wave reflecting off a vertical wall, two interesting observations were made: (i) a small eddy was generated towards the end of the reflection process and left behind the wave; and (ii) the contact angle formed by the free surface and the vertical wall never increased over 130 degrees. In the talk, both of the observations will be explained through boundary layer theory and the local similarity solutions of Stokes flow near the contact line, respectively. More details are as below:
Our experimental and theoretical study reveals that the wall boundary layer acts as drain for the flow near the free surface towards the moving contact line for most of the reflection process. However, during the last phase of the reflection process flow reversal occurs inside the wall boundary layer, and the free surface flow forms a jet ejected into the water body, which later evolves into a small eddy.
In a number of experimental measurements with very different length scales and geometrical configurations, where flow is dominated by inertia, there appears to be a limiting value for the advancing contact angle. Noticing that each steady motion of the moving contact line with different translation speed is linked by a hinged motion, the shear stress balance at the incipient of the hinged motion is considered. It is shown that the angular velocity is a decreasing function of the contact angle and approaches zero at the critical angle at which the local similarity solution becomes singular. Therefore the advancing contact angle cannot increase beyond the critical angle which is numerically very close to the experimentally observed values.