Simulations involving free surfaces and fluid interfaces are important in many areas of engineering. There is, however, still a need for improved simulation methods. Recently, a new efficient geometric VOF method called isoAdvector for general polyhedral meshes was published. We investigate the interface reconstruction step of isoAdvector, and demonstrate that especially for unstructured meshes the applied isosurface based approach can lead to noisy interface orientations. We then introduce a novel computational interface reconstruction scheme based on calculation of a reconstructed distance function (RDF). By iterating over the RDF calculation and interface reconstruction, we obtain second order convergence of both the interface normal and position within cells even with a strict L ∞ error norm. In 2D this is verified with reconstruction of a circle on Cartesian meshes and on unstructured triangular and polygonal prism meshes. In 3D the second order convergence is verified with reconstruction of a sphere on Cartesian meshes and on unstructured tetrahedral and polyhedral meshes. The new scheme is combined with the interface advection step of the isoAdvector algorithm. Significantly reduced absolute advection errors are obtained, and for CFL number 0.2 and below we demonstrate second order convergence on all the mentioned mesh types in 2D and 3D. The implementation of the proposed interface reconstruction schemes is straightforward and the computational cost is significantly reduced compared to contemporary methods. The schemes are implemented as an extension to the Computational Fluid Dynamics (CFD) Open Source software package, OpenFOAM R . The extension module and all test cases presented in this paper are released as open source. and are still used today e.g. in OpenFOAM and Fluent R , but are often not sufficiently accurate. Models assuming an infinitesimal interface thickness comprise of two steps: Interface reconstruction and interface advection. The most common reconstruction method is the piecewise linear interface reconstruction method (PLIC), where the interface within a cell is represented by a plane cutting the cell into two subcells. The resulting surface lacks C 0 continuity. Several approaches for the computation of the normal vector of the plane can be found in literature. In the widely used method by Youngs [3], the normal vector is calculated from the gradient of the volume fraction field. This method is easy to implement, also on three dimensional unstructured meshes, but lacks accuracy. In the least squares volume-of-fluid interface reconstruction algorithm (LVIRA) [4] an interface plane is projected into the neighbouring cells. The plane is used to calculate a volume fraction. The error of the calculated volume fraction in the neighbouring cells is minimized by changing the orientation of the plane. This delivers accurate results on all mesh types in three dimensions. However, the method needs a two dimensional minimizer in three dimensions which complicates the implementation and makes the m...

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One of the prevailing challenges in Computational Fluid Dynamics is accurate simulation of two-phase flows involving heat and mass transfer across the fluid interface. This is currently an active field of research, which is to some extend impaired by a lack of a common programming framework for implementing and testing new models. Here we present a new OpenFOAM based open-source framework allowing fast implementation and test of new phase change and surface tension force models. Capitalizing on the runtime-selection mechanism in OpenFOAM, the new models can easily be selected and compared to analytical solutions and existing models. As a start, the framework includes the following curvature calculation methods for surface tension: height function, parabolic fit, and reconstructed distance function method. As for phase change, interface heat resistance and direct heat flux models are available. These can be combined with three solvers covering the range from isothermal, incompressible flow to non-isothermal, compressible flow with conjugated heat transfer. By design, addition of new models and solvers is straightforward and users are invited to contribute their specific models, solvers, and validation cases to the library.

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