Design And Application Of Asymmetric Duct Of Ship Propeller

Non-uniform wake current of the ship causes an uneven load on propeller’s blades,which leads to the cavitation and noise problems of propellers of ships.In this paper,an asymmetric duct of ship’s propeller is designed to improve the wake current of ships.Firstly,the ICEM meshing software was used to model different series of accelerating ducts based on NACA airfoils.In addition,different series of accelerating ducts were calculated with STARCCM + software to study the effect of different duct lengths,attack angles and duct arches on improving the fluid,which,then,was used to analyzing the axial velocity on the propeller’s surface.Furthermore,some general rules were drew for engineering application.Secondly,it is necessarily to valid the method we used.In this point,the resistance performance of a bared KCS ship is calculated,to ensure the validity of the numerical method,compared with the experimental data.Next,the influence of the free surface on the axial wake at the propeller surface is analyzed.The result shows that the influence is very small,which should be noted is that without free surface the calculation is faster.Therefore,a numerical method without free surface,based on the aforementioned calculation and analysis,is adopted to calculate the wake field of KCS ship.Besides,the SST turbulent model is used when study the influence of different scales on the nominal wake field of the KCS ship.The results show that the reciprocal of the mean enthalpy fraction is positively correlated with the logarithm of the Reynolds number at different radii,and the peak value of the wake of the KCS ship decreases as the scale decreases,which represent that the small scale ships have a more obvious scale effect.Furthermore,based on the study of the wake current of a naked KCS ship,an asymmetric duct was designed to improve the axial wake distribution on the propeller surface.Therefore,the performance of the ship-duct model is calculated.With the analysis of the Taylor wake fraction on the surface of the propeller,it shows that the designed asymmetric duct of the propeller,ranging from 0 degrees to 80 degrees and from 280 degrees to 360 degrees,has an accelerating effect on the fluid,whereas a decelerating effect has been found in the range of 90 degrees to 270 degrees of the propeller’s surface.The comparison found that KCS ships with asymmetric duct do improve the wake current on the propeller surface and the overall wake current at the propeller’s surface became uniform.Finally,the performance of KCS ship with the designed asymmetric duct and the KP505 propeller is calculated to analyze the effect of the designed asymmetric duct on the fluid on the surface of the propeller.The analyzing process is divided into following steps.Firstly,with the aim of ensuring the accuracy of the numerical method,the performance of KCS ship combined with KP505 propeller is calculated,compared with the experiment data.Next,the performance of the aforementioned model added the designed duct is calculated,which focusing on the duct’s energy-saving effect on the flow and the axial wake current.The result shows that the asymmetric ducts have an accelerating effects on the fluid on the top half of the propeller while a decelerating effect on the lower half.Furthermore,it is noteworthy to point out that the designed asymmetric duct is able to decrease the ripple amplitude of the thrust force and torque on the propeller.