Research On Optimization Design And Parameters Of Marine Propeller

With the advances in marine industry, ship performances such as safety, energy-saving and environmental friendliness attract more and more attention from ship owners, users, and designers. As the most often-used ship propulsive device, performance design of the propeller becomes very critical. Meanwhile, as the ship becomes larger in size and higher in speed the demand for propeller to have better comprehensive performance becomes more and more important. In modern design practice, as an important measure to enhance the ship's economy, safety, and habitability, the propeller should be as efficient as possible and meanwhile, be free of cavitation when operating in the complicated wake field behind the ship in order to reduce the propeller-induced hull-structure vibration and noise as well as to extend the propeller's service lifespan by avoiding corrosion of blade material. It is very difficult for existing propeller theories and design methods to fulfill these contradictory requirements.On the other hand, for complex engineering design problems, optimization design techniques are often capable of reaching at an optimum solution under the constraint of many contradictory conditions. These techniques are finding more and more application in marine propeller design. In this thesis, the optimization of blade pitch and camber distributions is first studied by using a lifting-surface code integrated with the software iSIGHT. The design example is a five-bladed propeller for a container ship. CFD simulations are conducted to verify the design results. The CFD results indicate that, by specifying an appropriate chordwise loading distribution, the optimization procedure is capable of producing a camber surface with smoother pressure distributions without reducing the thrust and efficiency, which is favorable for the cavitation performance.The geometric parameters such as pitch, camber, skew, and rake are closely related to the loading distribution and hydrodynamic performance of the propeller. These relations are very important for the optimization design, however, no quantitative formulas exist to describe them. It would be very costly to search for them by model experiments. With the advances in CFD, it is becoming a mature technique to simulate the hydrodynamic performance, pressure distribution, and flow field of marine propellers by solving the RANS equations. As another work of this thesis, starting form a seven-bladed propeller as the prototype, systematic CFD simulations are carried out to study the influences of part of the geometric parameters upon the propeller performances. Two optimized designs are obtained finally, for which the open-water and cavity inception tests are conducted at the Towing Tank and Cavitation Tunnel of Shanghai Jiao Tong University respectively. The test results indicate that, the CFD prediction for thrust and torque is accurate enough and the optimized designs are superior to the prototype in terms of thrust, efficiency, and the cavitation bucket. In addition, it is possible to further enhance the cavitation performance by designing an appropriate tip-rake, though this may affect the efficiency a little.