[mix_mentzos]

Hi
From the help of FLUENT

"Non-conformal interface calculations are handled using the following two approaches:

Triangular face approach: triangulates the polygon intersection faces, and stores triangular faces. This approach involves node movement and water tight cells.
Virtual polygon approach: stores area vector and centroid of the polygon faces. This approach does not involve node movement and cells are not necessarily water tight cells. Hence gradients are corrected to take into account the missing cell area.
Both the algorithms calculate the intersection of the interface meshes, however using different approach for calculations.



Note: The former approach of making cells water tight sometimes results in concave cells, causing the interface creation to fail. For this reason the virtual polygon approach is more stable than the triangular face approach."

Pls can anyone explain me the meaning of water tight cells