IS - Ship Hydrodynamics. Experiments and Simulations On the numerical convergence properties of the calculation of the flow around the KVLCC2 tanker in unstruc- tured grids VII International Conference on Computational Methods in Marine Engineering MARINE 2017 M. Visonneau, P. Queutey and D. Le Touz´e (Eds) ON THE NUMERICAL CONVERGENCE PROPERTIES OF THE CALCULATION OF THE FLOW AROUND THE KVLCC2 TANKER IN UNSTRUCTURED GRIDS Ana Lu´ısa Rocha * , Lu´ıs E¸ca * and Guilherme Vaz † * Instituto Superior T´ecnico Universidade de Lisboa Av. Rovisco Pais, 1049-001 Lisboa, Portugal e-mail: ana.luisa.rocha@tecnico.ulisboa.pt e-mail luis.eca@tecnico.ulisboa.pt † Maritime Research Institute Netherlands (MARIN) 2, Haagsteeg 6708 PM Wageningen, The Netherlands e-mail: G.Vaz@marin.nl Key words: RANS, Numerical Error, Unstructured Grids, KVLCC2 Abstract. This paper addresses the estimation of numerical errors in the calculation of the flow around the KVLCC2 tanker at model scale Reynolds number in unstructured grids. The flow solution is based on the Reynolds-Averaged Navier-Stokes equations supplemented by the k - ω SST two-equation eddy-viscosity model using the so-called double-body approach, i.e. free surface effects are neglected. Grid refinement studies are performed for sets of grids gener- ated with the open source code SnappyHexMesh and with the HEXPRESS TM grid generator. Definition of grid refinement ratio in unstructured grids and its consequences for the estima- tion of numerical errors is discussed. Friction and pressure resistance coefficients and mean velocity components at the propeller plane are compared with reference solutions obtained in nearly-orthogonal multi-block structured grids with the same flow solver ReFRESCO. 1 INTRODUCTION Calculation of viscous flows around ships at model and full scale Reynolds numbers based on the Reynolds-Averaged Navier-Stokes equations has become standard practice for many CFD flow solvers. The two main challenges that such calculations present are: the ability to reduce the numerical error (iterative and discretization errors) to negligible levels and the selection of the turbulence model that leads to the smallest modelling errors. Recently, a Verification and Validation study has been performed for the KVLCC2 tanker [1] which is a ship geometry that has been thoroughly studied since the 2000 Gothenburg Workshop [2]. In [1], thirteen different turbulence models including one-equation and two-equation eddy- viscosity models and Explicit Algebraic Reynolds Stress Models are tested neglecting free surface 336