The stressful way of droplets along single fibre strands - A computational analysis

Droplets wetting and moving on fibres are omnipresent in both nature and industry. However, little is known on the local stresses the fibre substrates experiences and, in turn, the local forces acting on those droplets while moving on vertical fibre strands. This work is concerned with disclosing the influence of droplet volume, viscosity and chemical substrate heterogeneity on droplet motion. For this purpose, we pursue a computational simulation campaign by means of direct numerical simulations resolving all relevant spatial and temporal scales. On the basis of local simulation data, we evaluate and analyse effective viscous dissipation rates as well as viscous and capillary forces. We also assess the validity of an assumption which is frequently used in correlations for droplets moving on single fibre strands - neglecting the capillary force. Our computational analysis allows to falsify/verify this assumption for different scenarios and reveals that such correlations have to be applied with care, particularly when it comes to chemical heterogeneity of the fibre substrates.