Performance Prediction And Theoretical Design Research On Propeller In Non-uniform Flow

When the propeller operates in the spatially non-uniform velocity field behind the ship, the unsteady cavitation on the blades often causes the vibration of ship structure, the propeller noise and the cavitation erosion on the blade. To avoid or reduce these trouble induced by the unsteady cavitation, the theoretical design method for propeller and the blade section with the good cavitation performance are adopted to enlarge the cavitation bucket width and control the range and type of the cavitation on the blade. This enables propeller to operate in the non-uniform ship wake rather well.This paper adopts the theoretical method to research the problem on the performance prediction and the design of the propeller operating in ship wake systematically. The harmonic analysis and the panel method have been used to predict the unsteady performance of propeller. This computer program has been developed. The generalized inverse matrix method has been used to solve the nonlinear equal pressure Kutta condition in the harmonic analysis method that is the first time inland. The harmonic analysis method can save much computer time than the iterative scheme in time domain; it is very useful for the complex problem that needs a great of iterative. Present method is reliable and effective by the calculation results. It is very successful in the calculation of the pressures and hydrodynamic performance of the propeller in unsteady condition.The paper has improved the existing lifting-line and lifting-surface design method by including the rake and skew and solving the optimum circulation distribution with the optimum theory. The blade geometry is expressed with B-spline for the lift-surface method. The boundary condition on the blade is transformed to minimize the summation of the square of normal velocities, the fair blade geometry can be obtained by present technique and the design quality is better. By redesigning the existed propeller, the results show that the present method is reliable and accurate.This paper present an ideal and calculation method of the effective operatingcurve where cavitations characteristic is not change. Based on the lifting-line and lifting-surface method, using effective operating curve to control the cavitation type and "new section" design method to extend the width of cavitation bucket. The width will almost increase 30% than the common section. This technique can effectively improve the cavitation performance and resolve the design problem of propeller operating in unsteady flow field.The lifting-line and lifting-surface design method , the harmonic analysis method based on the panel method, new section design ways, the effective operating curves are integrated into a whole design system of the unsteady propeller , the design system is effective and reliable by the design example, the model test and the application to the full scale ship . This design system is suitable for the high speed ship with oblique flow and fat ship with the highly non-uniform flow field, and it is very valuable in the practical application.