Prediction Of The Hydrodynamic Performance Of Contra-Rotating Propellers By Lifting Surface Theory

In recent years, enhanced propulsion efficiency, saved energy and the reduced ships vibrates has become the significant duty which the ships designer author faces. Domestic and foreign extremely takes to the special propeller in this aspect function, and advanced in the ships has taken many measures, has created many new forms, theories also gradually started to consummate.The contra-rotating propeller is one kind of special propellers.The higher propulsive efficiency,better energy conservation effect and achieved the torque balance which it displays continuously receives the research worker's favour of various countries.Therefore it is vital significative to the prediction of the contra-rotating propeller hydrodynamic performance by using a theoretical method, in enhancing the ships propulsive efficiency,saving fuel consumption and reducing ships vibration.So, how studies can accurately prediction to the contra-rotating propeller hydrodynamic performance is more important.This article uses the lifting surface theory to predict the steady performances of contra-rotating propellers under the uniform flow , vortex lattice method is presented for calculating the loading distributions on all blades of a propeller, did not consider influence of propeller hub, a classics trailing vortex model is used for trailing vortex geometry.The contra-rotating propeller belongs to one kind of the built-up propellers, its hydrodynamic computation is extremely complex, must calculate interference velocity between each part, in this article ,the the mean value of interference velocity of attaches vortex and trailing vortex is calculate for predicting hydrodynamic force of the contra-rotating perpeller.In order to cause the result to be more reasonable, this article uses the iterative computation to convergence separately before determined the load of the forward and the after propeller respective, namely when calculates an propeller, its interference velocity which is by another propeller adds on inflow velocity to new inflow of this propeller, the continuously iterative computation for convergence. The thrust and the torque of the contra-rotating propeller has been calculated by this method, and its result is satisfying on the comparison and the analysis with the actual value.In order to increase the computation precision,in this article,a numerical method is presented for predicting the quasi-steady performances of the contra-rotating propeller based on the lifting surface theory.When using this method computation, its geometry separate and the trailing vortex model are same all with the steadyperformance.Its difference occupying to, in a computation period, along with two propellers blades relative position change, figures out these position interference velocities, and thrust forces and the torques of two propellers is calculated in these positions.Uses this method predicting the preformances of the contra-rotating propeller to be allowed to determine thrust force and the torque change rule in each position of a computation period , its computed result is satisfying.The research has built the certain foundation for the predict the unsteady performance of the contra-rotating propeller, and have the certain practical significance to prediction of other special propellers.