The Numerical Calculation Of Flow Field Around Large Naval Vessel

In recent years, with the globalization of economies, international ocean shipping and shipbuilding industry have been greatly developed. For reducing running cost and pursuing the maximal profit, many countries have been actively engaged in the design and the optimization of ship. The flow field around the ship which related to the ship resistance and stability has also been paid more attention. Ship model experiment relatively is the most reliable method for the prediction of ship performance, although it is time consuming, expensive, difficult to get detailed information of local flow field, more importantly such experiment has the scale effect, especially when carrying out the wind tunnel experiments for large ship, the situation of the flow around the ship can't be simulated actually,this is a big limitation for the precise simulation of ship performance by model experiment.But now, the ship CFD technology becomes an effective tool for the design of ship lines and the research of flow field around ship. Through numerical prediction of hydrodynamic and aerodynamic performance of ships, the design efficiency and the quality of ship engineering products are greatly improved, the period of research is shorted, and the devotion of the manpower and resources are reduced.The good stability, fast sailing speed and safe airflow field around the deck are necessary for a large naval ship sailing in the ocean, so it is obligatory to analyze the hydrodynamic and aerodynamic performance during the initial design period. With the use of ship CFD technology, this paper mainly discussed the impact of the stern profile of a large navel named RCSM on the resistance of the ship, hydrodynamic and aerodynamic flow around the hull.Firstly, based on the method of parent hull, two new stern lines for RCSM ship were designed in order to analyze the impact of stern lines on resistance performance of the ship. The new stern lines came from two ships with similar hulls but different sterns and were created by the Tribon-Lines software, then the numerical simulation of viscous flow field around ship were calculated by CFX software. According to the results,taking ship resistance performance as the determinant, the hull of RCSM-Ⅱposses lower resistance, smaller power consumption, weaker shape effect at the same speed, that indicates that the propulsion efficiency and the water flow of the ship named RCSM-Ⅱis better than others, so the square tail is suitable for high-speed vessels.Then, the hydrodynamic performance of the ship named RCSM was predicted and analyzed by the use CFD software. The numerical pools with two-dimensional section and three-dimensional hull were created in ICEM software, and divided with structural mesh. In virtue of the technology of sliding mesh and dynamic mesh provided by Fluent software, the numerical simulation of forced oscillation in various situations were calculated. After calculation, the velocity vector distributions during oscillatory motion and the force and moment curves of hulls change with time history were obtained. The additional mass and damping coefficient of the hulls were also calculated by theoretical formula. The results show that this method is perfectly suitable for the prediction of ship hydrodynamic performance and the analysis of flow around the ship. Meanwhile, some experiences in models creation, meshing (especially sliding mesh and dynamic mesh), boundary conditions setting were accumulated, which had laid a good foundation for the further use of CFD technology to study the hydrodynamic performance and flow fields around the ship.Finally, the simulation of the wind tunnel experiments about airflow field around the deck of RCSM ship was carried out by the use the CFD software. Two states that ships sail against the wind with and without rolling motion were mainly discussed. Velocity in critical points, flow field pressure contour, turbulence intensity, and velocity vectors and other data and physical parameters were obtained through the dealing of visualization. The distribution of the flow field and the area where turbulence was much active in key regions were discussed particularly. And during the calculation of airflow flied when ships sail against the wind with rolling motion, the technology of moving calculation domain and sliding mesh were used. By the comparison and analysis of the two different states, the results show that the velocity distribution of the airflow field around ship deck under steady situation without roll and unsteady situation with roll are different, especially in the equilibrium position where the angle velocity of the hull is the largest. When the hull rolled, the distribution of deck airflow field was changed with the movement of the roll angle; the area influenced by turbulence was increased and became unsteady, especially behind the floor, the airflow field was extremely drifting. The results provide some reference for the design of aircraft and carrier plane, and the process of calculation enable to accumulate some experience for the further study of unsteady flow field calculation at the state of ship shakes.