FREE SURFACE FLOW SIMULATION AROUND AN APPENDED SHIP HULL

This study brings forward the results of previously published work of free surface flow simulation around a fast ship model. Experimental measurements and numerical simulations of a fast bare-hull ship model form are now extended to the same ship form with appendices for a wide range of Froude numbers. The governing equations are discretized by means of an unstructured finite volume mesh. The standard k-ε turbulence model and Volume of Fluid Method to capture the two phase media are used. The total resistance, due to wave and wake fields of the ship model with appendages and the resistance of the appendages alone are calculated numerically, and compared with the experiments. The experiments and computations were performed for 11 different Froude numbers between 0.103 and 0.322. For Froude numbers up to 0.25, numerical simulations found to be quite in agreement with the experiments. It has been found that appendages increase the total drag mainly by increasing the pressure resistance, and the effect of the appendages becomes more important as the flow speed gets higher

WAVE FIELD GENERATED BY FINITE-SPAN HYDROFOILS OPERATING BENEATH A FREE SURFACE

The present paper focuses on the numerical investigation of the flow around the fully submerged 2D and 3D hydrofoils operating close to a free surface. Iterative boundary element method is implemented to predict the flow field. This study aims to investigate the aspect ratio effect on the free surface interactions and hydrodynamic performance of the hydrofoils under a free surface by using potential flow theory. Three different submergence depths and aspect ratios are studied in the wide range of Froude Numbers. In 3D cases, spanwise width of the numerical wave tank model is selected both equal and wider to the foil span, to observe the sidewall effects. Wave field seems to be two dimensional at low Froude numbers. On the other hand, signs of three dimensionalities are observed on the free surface structure for higher Fn, even the predicted wave elevations are very close to 2D calculations in the midsection. Increment in the Fn give a rise to the amplitude of the generated waves first, however a further increase in Fn has a lowering effect with the beginning of waves spill in the spanwise direction in the form of Kelvin waves. Free surface proximity and resultant wave field are also seeming to be linked with the lift force on the hydrofoil. As aspect ratio of the foil increase, 3D lift values are getting closer to those of 2D calculations. However, it is seen that, 3D BEM predictions of a hydrofoil under free surface effect cannot be considered two-dimensional even the aspect ratio is equal to 8

FREE SURFACE FLOW SIMULATION AROUND AN APPENDED SHIP HULL

This study brings forward the results of previously published work of free surface flow simulation around a fast ship model. Experimental measurements and numerical simulations of a fast bare-hull ship model form are now extended to the same ship form with appendices for a wide range of Froude numbers. The governing equations are discretized by means of an unstructured finite volume mesh. The standard k-ε turbulence model and Volume of Fluid Method to capture the two phase media are used. The total resistance, due to wave and wake fields of the ship model with appendages and the resistance of the appendages alone are calculated numerically, and compared with the experiments. The experiments and computations were performed for 11 different Froude numbers between 0.103 and 0.322. For Froude numbers up to 0.25, numerical simulations found to be quite in agreement with the experiments. It has been found that appendages increase the total drag mainly by increasing the pressure resistance, and the effect of the appendages becomes more important as the flow speed gets higher

NUMERICAL AND EXPERIMENTAL STUDY OF TURBULENT FREE SURFACE FLOW FOR A FAST SHIP MODEL

In this study the experimental and computational results for a fast ship model is presented. The Reynolds Averaged Navier Stokes (RANS) equations and the nonlinear free surface boundary conditions are discretized by means of an overset grid finite volume scheme. The experiments are performed at Istanbul Technical University Towing Tank basin. In the numerical turbulent flow calculations, the relationship between the Boussinesq\u27s hypothesis of turbulence viscosity and the velocities are obtained through the standard k-ε turbulence model. Simulations of turbulent free surface flows around the model are performed by using Star CCM+ solver and Volume of Fluid (VOF) model to capture the free surface between air and water. The total resistance of the ship model is compared with the experimental results. Bow and aft wave form developments are also investigated qualitatively. For Froude (Fn) numbers less than 0.25, the computations are found to be well satisfactory, giving efficient and accurate tool to predict curves of resistance. For relatively higher speeds (Fn>0.25) a low Reynolds number turbulence model may be more suitable to predict the resistance

Numerical study of ship motions and added resistance in regular incident waves of KVLCC2 model

In this study, the numerical investigation of ship motions and added resistance at constant forward velocity of KVLCC2 model is presented. Finite volume CFD code is used to calculate three dimensional, incompressible, unsteady RANS equations. Numerical computations show that reliable numerical results can be obtained in head waves. In the numerical analyses, body attached mesh method is used to simulate the ship motions. Free surface is simulated by using VOF method. The relationship between the turbulence viscosity and the velocities are obtained through the standard k − ε turbulence model. The numerical results are examined in terms of ship resistance, ship motions and added resistance. The validation studies are carried out by comparing the present results obtained for the KVLCC2 hull from the literature. It is shown that, ship resistance, pitch and heave motions in regular head waves can be estimated accurately, although, added resistance can be predicted with some error. © 2016 Society of Naval Architects of Kore