A Continuous Forcing Immersed Boundary Approach to Solve the VARANS Equations in a Volumetric Porous Region

  • Vergassola, Marco (Delft university of technology)
  • Colomes, Oriol (Delft university of technology)

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The study of the interaction between waves and porous structures is of great importance in offshore engineering. These structures are often used to dissipate the energy of incoming waves and protect the land. For this reason, with time a few porous models have been implemented in CFD solvers. These models represent an alternative to a microscopic representation of the porous region, whenever only the macroscopic effects are of interest. In these cases, a porous model can be used to model the flow-structure interaction, reducing the computational burden. Currently, in OpenFOAM®, it is only possible to define a static porous region. However, a dynamic region would, for example, enable the use of porous regions for the study of perforated floating structures and moving porous objects. In OpenFOAM®, a volumetric porous region is defined similarly to the Immersed Boundary Method (IBM) in its continuous forcing formulation. Firstly, a field is defined to mark and track the porous cells within the fluid mesh. Then, a forcing term is introduced in the momentum equation to simulate the presence of the porous body. In this work, a new solver is developed to solve the VARANS equations inside a volumetric porous region using a continuous forcing IBM. Compared to the existing solvers, this does not require a conformal mesh and, in principle, it allows the definition of dynamic porous regions. The use of a simple Cartesian mesh also represents an important advantage when dealing with complex geometries. The solver is tested by simulating a static porous cylinder in a 2-dimensional constant flow at both Re=40 and Re=100. Both quantitative and qualitative results are promising. More tests, including the interaction with waves, are currently being performed. So far, the solver presents a speedup value of 1.88 compared to traditional conformal mesh solvers.