Coupled level-set volume of fluid simulations of water flowing over a simplified drainage channel with and without air coflow

The motivation for this paper is to predict the flow of water over exterior surfaces of road vehicles. We present simulations of liquid flows on solid surfaces under the influence of gravity with and without the addition of aerodynamic forces on the liquid. This is done using an implementation of a Coupled Level Set Volume of Fluid method (CLSVOF) multiphase approach implemented in the open source OpenFOAM CFD code. This is a high fidelity interface-resolving method that solves for the velocity field in both phases without restrictions on the flow regime. In the current paper the suitability of the approach to Exterior Water Management (EWM) is demonstrated using the representative test cases of a continuous liquid rivulet flowing along an inclined surface with a channel located downstream perpendicular to the oncoming flow. Experimental work has been carried out to record the motion of the rivulet in this case and also to measure the contact angle of the liquid with the solid surface. The measurements of the liquid/solid characteristics such as equilibrium and dynamic contact angles are described along with the analytical expression for contact angle vs. capillary number used in the CFD code. The results from the simulations are compared to experimental measurements. The simulations are carried out with air co-flows of 0, 0.5 and 10 m/s. The simulations are seen to reproduce physical phenomena such as the liquid pinning at sharp corners and the longitudinal stretching of the rivulet with higher air velocity.