Numerical Simulation Of The Viscous Flow Around A Twin-skeg Ship

Compared with traditional ship forms, the Twin-skeg ship developed in the 1980s has its advantages of lower resistance, higher propulsive efficiency, smaller hull vibration, better maneuverability and less stern- sinkage. Twin-skeg ship has become one of the main high-speed passenger ships in Yangtze River, and widely used as coastal freighters, nonstop container ships, shallow-water motor barges, push boats ferry boats and chemicals transport ship. Through 20 years' research, the design and development of Twin-skeg ships has made remarkable progressSupported by the project "new ship forms for Chishui River shipping" offered by the western region-development office of the Ministry of Communications of the People's Republic of China, the numerical simulation of the viscous flow around a Twin-skeg ship designed in this project has been made. For such a shallow water Twin-skeg ship with high block coefficient and big B/T, lacking references so far, numerical simulation for viscous flow is a tough task, especially in the grid generation and corresponding numerical treatment near the stern.In this paper, the commercial software FLUENT is used to calculate the viscous flow field around a ship with Twin-skeg, without taking into account the impact of wave-making resistance. For such ship form with a stern of complex geometric shape, the flow field changes rapidly. It is inconvenient to adopt structured mesh, so a structured-unstructured mixed type mesh is employed in this computation. To reduce quantity of mesh cells and to improve precision, convergence, we adopt the self-adapted H-C type structured mesh in the main part of computation field, and use unstructured mesh only at the local region near the stern fin. Computation mesh is generated by the algebra method, and then optimized through an elliptical mesh generator to improve the orthogonality and the smoothness. The preprocessed mesh is exported by mesh file and imported into FLUENT. With k- e turbulent model and wall function presented by Launder and Spalding, numerical results of viscous resistance coefficient, isoplethic maps of velocity and stress contributions areobtained. The result shows that the curve of viscous resistance coefficients calculated lies close to the curve of experiment values reckoned from the form factor (1+k) ,as values of wave pattern measurement and wave pattern analysis.The study provided a helpful experience for the numerical simulation of viscous flow around such a complex ship form.