Experimental And Numerical Study On Hydrodynamic Performance Of Bow Thrusters

In recent years,the function of the ship is continually changing with the advances in technology.The requirement for the ship positioning performance is getting higher and higher,which leads to increasing demand for the bow thruster.However,the bow thruster is often located on the vibration-sensitive areas,such as the accommodation,the restaurant,the conference rooms and the cab.On the other hand,there exists thrust reduction phenomenon.Therefore,it is necessary to make a study on the hydrodynamic performance of the bow thruster.Theoretical research,numerical simulation and model test are three kinds of methods often used in the study of ship hydrodynamic performance.The theoretical research can clearly and universally reveals the inherent law of the flow,but it is applicable only for some special theoretical model.Numerical methods can solve some complicated flow problems that cannot be solved by theoretical research methods,such as the interference among hull,propeller and rudder,the problem of dam-break,the problem of unsteady cavitation,details of the flow field around the hull,fluid-soild coupling.Reliable data can be obtained by model test,but the similarity criteria cannot be completely satisfied.And there exists size limitation and tank boundary impact in the model test.Therefore,the combination of numerical simulation and model test is often adopted in the current researches on ship hydrodynamics,in which the credibility of the numerical results is ensured by comparing with the model test.Experimental and numerical study of a bow thruster has been made in the paper.On the one hand,the open water test of the bow thruster and the hydrodynamic performance test of the bow thruster with ship model were carried out by using a special dynamometer.On the other hand,the flow field inside the tunnel is numerically simulated through solving the unsteady RANS equation by the finite volume method.The pressure fluctuation on the tunnel wall,the open water characteristic curve and thrust coefficients of the bow thruster under different flow angles are obtained.The numerical results agree very well with the measured data of the model test.The conclusions drawn in this paper can provide a valuable reference for the design of the bow thruster and hence plays a guiding role for engineering practice.The numerical results show that:1)The pressure fluctuations are concentrated on small areas near the blade's tip.By comparing the pressure fluctuation on the tunnel wall under different flow directions,it is found that the fluctuating pressure is related to the complexity of the flow field.The smoother the flow is,the smaller the pulse pressure becomes,and vice versa.2)The thrust reduction of the bow thruster reaches above 20% at certain angles due to Coanda Effect and the interference of multi-propeller.Details of the flow field with Coanda Effect are also presented in the paper.