The Effect Of A Front Duct On Hydrodynamic Performance Of Highly Skewed Propeller

As an energy-saving device,the front duct has been gradually applied to various ships;however,there are few studies on the influence of the front duct on the hydrodynamic performance of the propeller.It is usually studied together with the hull;This paper takes the No.19 A duct and a highly skewed propeller of the warship as research object.The changes of the hydrodynamic performance of the propeller were studied when the parameters of the front duct were changed.The internal mechanism was studied by analyzing the flow field,which is beneficial to the design and installation of the front duct and the improvement of the propeller performance.After the propeller model is established and the meshing is completed,the verification of the open water performance of the propeller is carried out.The influence of different turbulence models on the numerical results was compared,It is found that the error between the numerical calculation results and the experimental values is the smallest when using the SST k-? turbulence model.The pressure distribution of the propeller blades was analyzed,and the propulsion mechanism was studied.When only the No.19 A duct was in the field,it was found that the duct accelerated the water flow immediately behind of the duct.Then,on the basis of numerical verification,study on the influence of the distance between the front duct and the highly skewed propeller,the duct diameter and the angle of attack on the hydrodynamic performance of the highly skewed propeller.The study found that when the distance is reduced,the water flow into the disk plane is accelerated,and the propeller thrust is reduced.When the diameter is reduced and the angle of attack is increased,the hydrodynamic performance of the propeller is improved step by step.Through the analysis contour of the axial velocity,pressure and longitudinal profile of the axial velocity,vorticity at different distance,diameters and angles of attack,It is concluded that the improvement of the hydrodynamic performance of the propeller is mainly due to the fact that the water flow near outside the duct is affected by vortex generated by front duct,which reduces the flow velocity behind it.When the diameter is reduced,the low-speed flow can act on the outer disk plane of the highly skewed propeller,and the effect is further enhanced when the angle of attack is increased,so that the performance of the highly skewed propeller is gradually improved.Finally,the force of the duct and the hydrodynamic performance of the thruster are analyzed.It is found that in the case of low advance coefficient,the duct can provide a certain thrust due to the influence of the propeller.At this time,the thrust of the thruster is greater than the thrust of the propeller,and the required torque is reduced,thereby improving the efficiency of the thruster under the low advance coefficient.In the case of a high advance coefficient,the hydrodynamic performance of the thruster is reduced due to the excessive resistance of the duct.At last,the aspect ratio of the No.19 A duct was optimized,and it was found that reducing the aspect ratio would reduce the thrust and resistance of the duct to different degrees.It is recommended that the aspect ratio of appropriate size should be selected to optimize the overall propulsion of the thruster in the actual engineering application.