Uncertainty of rivulet flows on heterogeneous surfaces – A numerical study

Abstract

This paper presents a three-dimensional numerical simulation of water flow on an inclined plate using the software package OpenFOAM. We specifically investigate the influence of a heterogeneous surface on the flow pattern and the degree of wetting. By analyzing 400 simulation results a recently developed method for applying random contact angle inhomogeneities to surfaces is investigated. The simulations were carried out using the empirical contact angle model, which enables stable rivulet development. Part of the analysis is conducted with the help of the statistical software Dakota, which provides information about the probability distribution of the amount of wetted area when varying the two important influencing factors: the amplitude of the contact angle disturbance or the size of contiguous hydrophobic or hydrophilic areas. The results show that a variation of the two input parameters as desired leads to the introduction of a random component and thus to a change in the flow behavior. However, the changes remain within a narrow range around the mean value and produce only a few outliers, which occur mainly at large contact angle disturbance amplitudes and thus indicate the determining influence of the amplitude. The method has proven useful for performing several runs of the same simulation configuration for collecting statistics. Furthermore the inclination of the plate and the contact angle using a constant contact angle model are varied. Here, a clear dominance of the influence of the inclination also manifests over a wide contact angle range.