Experimental Study And Theoretical Calculations Of Edge-cut Propellers

It will be of high propulsive efficiency and low energy consumption for a ship when the hull, engine and propeller match well. This should be what naval architects and ship operators go in for. After many years of operation, the propeller may be overloaded due to some reasons such as fouling of the hull, ageing of the engine and corrosion of the propeller. As a result, the designed optimal matching point between the hull, engine and the propeller will be offset. When the hull and engine are fixed, it is the only optional solution to modify the propeller in order to make the engine work near the rated condition.It is an easy and feasible solution to modify the propeller by cutting its edge. In this paper, it is carried out to study on the two propellers which are cut on the blade tip and the trailing edge respectively by tests and theoretical calculations, which offers the technical support for the modification of the propeller in the practice.The open water performance of the MAU4-50 propeller was obtained by carrying out the open water test with the propeller being cut on the blade tip at different diameters in this paper. The results from the tests show that the thrust coefficient and torque coefficient are increasing with the increase of the cutting amount at the same advance coefficient, while the open water efficiency is decreasing. As a result, the relationship between the relative cutting amount of the diameter and the relative variation of the MAU propeller speed in form of charts are derived from the experimental data. The results from the tests of the KMM4-46 propeller which was cut on trailing edge at different chord lengths show that the thrust coefficient, the torque coefficient and the open water efficiency are decreasing with the decrease of the impeller solidity ratio, and the relationship between the relative variation of KMM propeller speed and the relative cutting amount in the form of charts are also derived from the results.The lifting surface theory is carried out to calculate the open water performance of the two propellers under different circumstances in order to study the accuracy and the feasibility of predicting the open water performance of the propeller in theoretical way. The same changes of open water performance of the two propellers occur in two theoretical ways versus the tests. Meanwhile, the computational fluid dynamics method is also used to predict the open water performance of MAU propeller. Comparison results show that predictive accuracy of numerical simulation study is higher than that of the lifting surface theory. The reason is that the viscous flow is dealt with the real flow while the lifting surface theory is based on the potential flow. It may be due to the simplification of boundary conditions and wake model. On the whole, the two methods are well used to predict open water performance of propellers.