A Comparative Study On The Lines Design Of Bulbous Bow Of Large Ship By CFD

Because of the energy crisis and the continuing economic crisis, research on a new ship is being quickly done to reduce the ship resistance in many countries. Based on effect of the energy-saving bulbous bow, the four ships with different bulbous bows were selected,whose resistance and viscous flow field were forecasted by CFD. A bulbous bow lines that is propitious to reduce resistance was obtained by comparing these results, which can provide a reference to optimize the part lines of ship.These models of ship hull were created by the method of joint Tribon system, Auto CAD and ICEM. The method of block structured grid was used to mesh the complex large ships with the bulbous bows in this paper, and the impact of the grid number and time step on the convergence process was also discussed. Through a large number of tests, the number of the grid that can get more accurate results was obtained, as well as a series of simulation time step changed method in process of simulation count, were obtained.First, a ship with bulbous bow with the experimental data was selected to make a verifying and analysis in this paper. The commercial CFD software-CFX was applied to simulate the numerical calculation of ship viscous flow field. The resistance calculation results were contrasted with the experimental data and theoretical data, which showed that the numerical results were closer to the experimental data of the error within 10%, and there was a great difference between numerical results and theoretical data with an error of 10% -30%. The distribution maps of free surface and the speed at propeller disk showed that the VOF method can simulate the free surface and the wake more accurately.Then three ships with a similar form to the calculation case but different bulbous bow (immersed type, ordinary type, and raised type) were selected for the numerical simulation of viscous flow. To make comparable results, the three ships were scaled to the same size with the calculation case. The results showed that: at the lower speed: the wave arisen by the ship with a raised bulbous bow is larger than the others. At the higher speed: the wave arisen by the ship with a raised bulbous bow is the smallest among them, and its flow field is more homogeneous than the others. The two ships with ordinary bulbous bow and raised bulbous bow had obvious"virtual length", which became longer along with the increment of ship speed, thereby reducing the residual resistance. The numerical results showed that: If Fr <0.23, then the resistance of the ship with raised bulbous bow is between the other two ships. If Fr >0.23, then the resistance of the ship with raised bulbous bow is the smallest, and the resistance of the ship with immersed bulbous bow is the largest.The different effects of flow field in different forms and different sizes of bulbous bow could be seen in the simulation results, which can provide an effective approach to optimize the lines of ship from the performance of resistance.