Turbulent flow separation around a ROV body

Abstract

This report is the result of the master’s thesis developed at the University of Galati in the frame of the EMSHIP Erasmus Mundus Master Course. It deals with the numerical simulation of the turbulent flow around a fully submerged Remotely Operated Vehicle (ROV) with ellipsoidal body using the commercial CFD code FLUENT. This ROV has as propulsion system four ducted propellers, two for horizontal displacement and two for vertical displacement. The purpose of this study was to investigate the propulsive performance of this underwater vehicle by computational fluid dynamics method. Two types of 3D geometry of this ROV have been created using the CAD software Rhinoceros 3D. • The ellipsoidal ROV without propellers called bare body; • And the ellipsoidal ROV with channels and propellers as defined in the scope of work. It is called ROV body. Propellers are modeled as active disk and mounted in two cylindrical channels parallel with x axis and the other two in channels parallel with z-axis. FLUENT code was employed to compute the incompressible RANS equations on structured and unstructured mesh by using a finite volume technique in order to access the forces acting on the ROV and the flow field structure. In order to choose the best turbulence model suited for the viscous incompressible flow around ROV body available in Fluent, we apply a Verification and Validation method. In order to investigate the numerical error we have defined 3 types of mesh on the bare body, fine, medium and coarse. With each type of mesh we have run computations with all models of turbulence. After that we will compare with the towing tank results, in order to compute the modeling uncertainty. The simulations are performed at Reynolds number =7.68∗10^5, which correspond to the service speed of 3 knots in freshwater conditions according to FLUENT. The numerical simulations were performed on the ROV at five speeds of interest ranging from 1 m/s to 2 m/s. Propellers were substituted by an active disk for which the pressure jump is defined as boundary conditions. Conclusions and recommendations are presented, as well as suggestions about future work related to the topic.