Research Of Design Method For Highly Skewed Propeller

When the propeller works in the non-uniform or terribly non-uniform flow field behind the ship, periodic unsteady force is generated on the blade of the propeller due to the non-uniform characteristic of the flow field. As a propulsion device different from the conventional propeller, the highly skewed propeller can often be accompanied by the flow field with a "mismatch" to reduce the harm arising from this phenomenon. Based on this characteristic of the highly skewed propeller, the research of design method on the highly skewed propeller is carried out.Firstly in this paper, based on the classical lifting-line theory, the theoretical method was used to study the effect of including the rake and skew. The integral expression of the induced velocity induced by the eddy tie which worked on the lifting-line including the rake and the skew was deduced. To avoid infinite integral, discrete vortex method was adopted to calculate the induced velocity. The results indicated this method was reliable and effective, which was also reliable in solving the optimal circulation. Two numerical calculation methods were founded aimed at solving of the optimal circulation. The results indicated that the rake and skew had some effect, which was little on optimal circulation distribution. In addition, the rake and skew had great effect on induced velocity. Especially the skew had the adverse effect on axial induced velocity compared with tangential induced velocity.Then the paper focused on lifting-surface design method of the propeller. Discrete vortex lattice method was adopted for numerical calculation and the method of modifing the camber surface brought out by Kerwin was also introduced. The hydrodynamic calculation of the propeller was presented, considering the leading suction and viscous effect.In addition, considering the characteristic of non-uniform flow field, the design of highly skewed propeller, which worked in non-uniform flow field was mainly divided into harmonic analysis of ship wake field, initial lifting-line design, lifting-surface design, panel method for predicting steady performance and optimization of skew distribution in this paper. Considering the difference of the conventional propeller and highly skewed propeller, the intension-estimating method for highly skewed propeller was presented and the effects on stress distribution by the rake and skew were analyzed, which can be used to offer some reference. The paper presented optimization method for the skew distribution of highly skewed propeller. The introduction of particle swarm optimization (PSO) method combined panel-method for predicting unsteady performance and FFT method made the skew distribution optimized. Mainly pulsatile amplitude of unsteady thrust was decreased. It indicated that this method could be used to improve the performance of the propeller worked in non-uniform flow field by changing the skew distribution.Lastly, relevant examples were built for designing the conventional propeller and highly skewed propeller worked in the open water. By redesigning the existed propeller, the results show that this method was useful and effective not only on designing the conventional propeller but also on designing the highly skewed propeller.