Simulation of ship in self propulsion with different CFD methods: From actuator disk to potential flow/RANS coupled solvers

RANS solvers are becoming a standard for the numerical prediction and for the analysis of the flow feature around the hull, including the presence of the free surface and the computation of hydrodynamic forces. Panel Methods, thank to their computational efficiency, can still, and successfully, be applied for the analysis and the design of marine propellers. Self-propulsion requires an accurate solution of both the aspects that, moreover, strongly interact. Time and spatial scales, for the propeller and for the hull, are unfortunately very different and a complete RANS solution would require non negligible computational resources. A coupled solution, in which hull is solved through RANS, propeller through panel method and the solutions matched via Body Forces and effective wake is presented as a fast and robust tool for ship self-propulsion characteristics evaluation. First a simple "unsteady" axial actuator disk, which momentum source strength is evaluated from the instantaneous ship hull drag, is adopted to compute wake and thrust deduction factors. Finally a more consistent model, based on an iterative approach and on unsteady body forces, is applied in order to represent the three dimensional effects related to the effective blade geometry. Results will be compared in order to identify the capabilities of the coupling technique and the hypothesis of practical applicability of such kind of procedure.