Simulation of Free Surface in Open Channels with OpenFOAM: Some Experiences and Recommendations

In recent years, three-dimensional computational fluid dynamics (CFD) modeling of free-surface open-channel hydraulics has gained substantial popularity. In these applications, e.g., hydraulic jump, the free surface changes greatly and thus it is desirable to capture the spatial variable of water surface. Among many commercial and free CFD packages, the open-source platform OpenFOAM has been used extensively by both academic and industry in many hydraulics-related applications. OpenFOAM is essentially a generic partial differential equation (PDE) solver. Despite its increasing usage in hydraulics, there are several issues encountered by both the authors and others. One of the major problems is how to properly set the boundary conditions for free-surface open-channel flows. The solver for such simulation is usually the volume-of-fluid (VoF) solver interFoam which is part of OpenFOAM. The difficulties are mainly rooted in the unique way of handling pressure in interFoam and the VoF algorithm. Based on detailed analysis of the algorithm within the interFoam solver, and the experiences of the authors, this paper provides some solutions and recommendations on how to properly use OpenFOAM for hydraulic engineering problems. Some modifications to the interFoam solver are necessary. An array of examples will be given for demonstration.