Numerical Study On Hydrodynamic Performance Of Overlapping Propeller

Growth in the world economy has led to growth in the marine transportation.With the increasingly serious issue of energy shortage and environment pollution,the techniques of ship propulsion and its energy saving gets more and more attention.And it also promotes the development of a variety of special and efficient propellers.As a new type of the special propeller,overlapping propeller has energy saving potential,which fully utilizes bilge vortices to obtain high propulsive by being fixed and designed properly.It is particularly suitable for the full-scale ship with U-shaped stern.By using numerical calculation method,this paper studies hydrodynamic performance of overlapping propeller and its influence factors.Compared the propulsion performance of overlapping propeller and conventional propeller,the result could further reveal the energy saving mechanism of overlapping propeller to provide technical basis for its application promotion.The main contents of the paper include: In this paper,ICEM is used to build three-dimensional model of the propeller and computational grid.Fluent is used to calculate hydrodynamic performance of overlapping propeller,and the result is processed by CFD-POST.To verify the effectiveness and accuracy of numerical calculation methods,First,the numerical simulation of DTMB P4119 propeller open-water performance was accomplished,and the comparisons between CFD and EFD shows the numerical simulation were consistent with experimental results and could give more detail information.Taking overlapping propeller system made up of two P4110 propellers as an example,it discusses the effect of the composite parameters on hydrodynamic performance.Studies indicate :(1)Because of the overlapping area,the fore propeller and aft propeller interfered with each other.The hydrodynamic performance of the two propellers is different from that of single propeller.The difference changes over L and is more intense on aft propeller.When L=0.75 D,the load of fore and aft propeller is equal.(2)The difference of hydrodynamic performance between fore propeller and aft propeller changes over θ,too.So,the paper advices it’s better to decrease θ as far as possible while the two propellers can’t clash.(3)When L =0.75 D,θ =0 °,with the increase of ψ,the load of fore propeller has smaller changes,while the load of aft propeller dropped significantly.Hydrodynamic performance of the aft one is lower than that of the fore propeller.So,this paper advices ψ is better to be equal to 0 degree.In order to make a further reveal of energy saving mechanism and effect of overlapping propeller taking use of bilge vortices,we make a numerical simulation on self-propelled model on ship with on propeller、single propeller or overlapping propeller.Firstly,we have analyzed the stern flow field of ship without propeller by observing circumferential flow degree around propeller disk at the different position of transverse stern: when the propeller disk placed at the central of stern,the tangential velocity of propeller disk is roughly left-right symmetrical;When the propeller disk placed at the center of bilge vortices,the tangential velocity is asymmetrical which reflects the obvious pre-swirl effect.When the overlapping propeller placed at the center of bilge vortices and the rotation is contrary to bilge vortices’.Self-propeller model numerical calculation result shows that the propulsion efficiency is improved about 8% than that of ship with single propeller.On the one hand,this income contains bilge vortices energy recycled by overlapping propeller;On the other hand,it also includes the improvement of propeller efficiency with loading reducing from single to two propellers.The relevant research methods and conclusions of this paper have certain theoretical and applied value on naval architecture for the promotion of energy-saving and emission reduction technology.