Coupling techniques between sub grids and across interfaces

Overset grids allow strong flexibility when computing flows around maritime constructions. For example, to allow motions between bodies inside the computational domain. Examples are a horn rudder in which the rudder flap oscillates, or ships passing each other in confined waters. If the motions between the bodies become too large, the quality of deforming grids will be compromised and therefore overset grids are the more reliable alternative.
Interfaces are important as well in many simulations for maritime applications. A RANS-RANS sliding interface can be used to simulate flows involving a rotating propeller aft of a ship. The propeller rotation is modelled by dividing the computational domain into two subdomains, one around the ship and one around the propeller, where the latter domain rotates, and the flow data is exchanged between the sub domains along a sliding interface. Another kind of interface is a periodic boundary, which can be used, for example, to analyse a single blade of a propeller instead of the full propeller in open water. In this paper we discuss the effect of using an implicit coupling mechanism between the sub grids of the overset grid approach, or between both sides of an interface. The use of overset grids requires an interpolation of the flow from one sub grid to the other and the use of interfaces requires an interpolation across interfaces. These interpolations use data from the previous iteration when variables are explicitly coupled, and data of the current iteration when variables are implicitly coupled.