A Study On Design Of Marine Propellers Based On Surface Panel Method

Propellers and their various combinations are primary propulsion forms of modern ships, and their design and performance calculation have increasingly become fundamental goals for both designers and researchers in the field of fluid mechanics. When the propeller operates in the spatially non-uniform velocity field behind the ship, the unsteady cavitation will appear on blades which can cause the vibration of ship structure, propeller noise, cavitation erosion and rediation noise. Therefore, in the propeller design process, in order to gain the best performance, designers should roundly consider the propulsive efficiency, cavitation, vibration, noise and erosion, and other performance requirements.Compared with the traditional chart design method of propellers, the theoretical method is more flexible and adaptable. Because it could be widely used in designing various types of propellers, and it has fluid mechanics advantage of analyzing design constrait factors such as loads of blades, circulation distributions, the theoretical design could decrease propeller vibration and noise, and it could further improve the propeller performance. In this paper, the systemic theoretical design method of the marine propellers was studied. The main work is as follows:(1) The 3D hydrofoil design in numerical way based on the surface panel method is investigated. The hydrofoil design process is improved, with specified maximum thickness, lift, and type of pressure distribution in hydrofoil sections. In the design process, the 3D effect of hydrofoil is considered by simulating vortex sheet roll-up. To improve the efficiency and quality of the design method, B-spline is applied to describe the geometrical profile of hydrofoil sections.(2) The determination of the optimum radial circulation distribution of the propeller is investigated based on the improved lifting-line model and the improved particle swarm optimization algorithm. The traditional lifting-line method based on moderately loaded propellers is improved. The axial, radial and tangential induced velocities are considered, and the kinematics boundary condition that the direction of vortex line is consistent with the local flow field direction is fulfilled by iteration calculation. Therefore, the improved lifting-line model could be applied on many conditions including the heavy loaded condition to determine the optimum radial circulation distribution of marine propellers. Meanwhile, an improved particle swarm optimization algorithm based on artificial intelligence theory is proposed. A mutation strategy for premature convergence particles is added in the algorithm. The mutation strategy could solve non-linear optimization problems with or without restraints. Finally, the traditional variational calculus method is replaced by the more efficient, high-speed convergent optimization method to optimize the propeller radial circulation distribution.(3) The marine propeller numerical design method based on the surface panel method is investigated. The propeller surface is described by B-spline. The section profile is corrected to fulfill the specified type of pressure distribution of the propeller blade section. The skew distribution of propeller blades aiming at reducing axial pulsed forces is optimized based on the artificial intelligence algorithm. The parallel optimization algorithm based on OpenMP is also developed for multiple-cpu computers in order to improve the computation efficiency.(4) According to the characteristics of mini-autonomous underwater vehicles and specific engineering cases, a three-blade, small expanded area ratio propeller series is developed and its design chart is produced. This propeller series is suitable for light-loaded, low speed, and low motor rotational speed underwater vehicles. A series of three-blade, small expanded area ratio propellers are designed and tested in open water. The numerical method of propeller performance prediction by the surface panel method is modified correctly by open water test data, to further increase prediction precision. Based on large numbers of open water performance data calculated by the surface panel method, a three-blade, small expanded area ratio propeller series design chart is produced.By designing some designed propellers, it turns out that, newly designed propellers have high efficiencies, given flattop pressure distributions and more moderate blade loads. Those features will benefit the cavitation performance of propellers and decrease the vibration of ship structure and rediation noise. Therefore, the marine propeller design method in this paper is proved effective, reliable and practical.