Analysis of an unsteady quasi-capillary channel flow with Time Resolved PIV and RBF-based super resolution

TL;DR

This study combines advanced imaging and super-resolution techniques to analyze unsteady quasi-capillary flows, revealing complex vortex dynamics and limitations of classic contact angle models under inertial conditions.

Contribution

It introduces a novel application of RBF-based super-resolution to TR-PIV data in unsteady capillary flows, providing new insights into interface dynamics and flow structures.

Findings

Large counter-rotating vortices observed near the interface

Classic contact angle laws are inadequate for dynamic wetting at high accelerations

Flow influence extends several capillary lengths below the interface

Abstract

We investigate the behaviour of accelerating contact lines in an unsteady quasi-capillary channel flow. The configuration consists of a liquid column that moves along a vertical 2D channel, open to the atmosphere and driven by a controlled pressure head. Both advancing and receding contact lines were analyzed to test the validity of classic models for dynamic wetting and to study the flow field near the interface. The operating conditions are characterized by a large acceleration, thus dominated by inertia. The shape of the moving meniscus was retrieved using Laser-Induced Fluorescence (LIF)-based image processing while the flow field near was analyzed via Time-Resolved Particle Image Velocimetry (TR-PIV). The TR-PIV measurements were enhanced in the post-processing, using a combination of Proper Orthogonal Decomposition (POD) and Radial Basis Functions (RBF) to achieve super-resolution of the velocity field. Large counter-rotating vortices were observed, and their evolution was monitored in terms of the maximum intensity of the Q-field. The results show that classic contact angle laws based on interface velocity cannot describe the evolution of the contact angle at a macroscopic scale. Moreover, the impact of the interface dynamics on the flow field is considerable and extends several capillary lengths below the interface.