OpenFOAM is the leading free, open source CFD software operates on Linux kernel operating system. Nowadays this software is the most widely used free CFD package. However, its learning resources and theoretical descriptions are quite limited. Can anybody help me find reliable and complete resources for OpenFOAM software's theoretical and mathematical background?
Particularly for details on the numerical aspects of the solvers of "Hybrid VOF-Eulerian Multi-fluid Methods" such as multiphaseInterFoam, multiphaseEulerFoam, and interMixingFoam which are addressing multiphase flows with more than three phases.