A sharp and conservative method for modeling interfacial flows with insoluble surfactants in the framework of a geometric volume-of-fluid approach

TL;DR

This paper introduces a novel sharp, conservative volume-of-fluid numerical method for accurately modeling insoluble surfactant effects on interfacial flows, handling complex topologies with high precision.

Contribution

The paper presents a new geometric volume-of-fluid approach that preserves interface sharpness and improves accuracy in simulating insoluble surfactant-laden flows over existing diffusive methods.

Findings

Higher accuracy and faster convergence than diffusive approaches

Effective handling of complex interface topologies

Revealed surfactant concentration effects on bubble-wall interactions

Abstract

Insoluble surfactants adsorbed at liquid-liquid or gas-liquid interfaces alter interfacial tension, leading to variations in the normal stress jump and generating tangential Marangoni stresses that can dramatically affect the flow dynamics. We develop a three-dimensional, sharp and conservative numerical method for modeling insoluble surfactant-laden interfacial flows within a volume-of-fluid framework. This method contrasts with diffusive transport algorithms commonly employed in the Eulerian framework. The proposed method preserves the zero-thickness property of the interface, ensures accurate calculation of the surfactant concentration, and robustly handles complex topological changes. The interface evolution is captured using a geometrical volume-of-fluid method, with surfactant mass sharply stored at the reconstructed interface. The advection term in the surfactant transport equation is discretized implicitly in conjunction with the geometrical advection of the volume fraction of one of the fluids, thereby eliminating numerical inconsistencies arising from discrepancies between the actual and computed interface areas. Additionally, the diffusion term is discretized along the reconstructed interface, preventing artificial diffusion normal to the zero-thickness interface. Benchmark tests demonstrate that the proposed method achieves higher accuracy and faster convergence compared to existing diffusive approaches. Finally, we apply the method to investigate the interaction of a surfactant-laden rising bubble with a vertical wall, revealing a transition from near-wall bouncing to migration away from the wall as the surfactant concentration increases.