The Numerical Study On Hydrodynamic Performance Of Surface Piercing Propeller With Different Ventilation Modes

As a new type of specific high-performance propeller,surface piercing propeller has been more widely used in high-speed crafts.Nevertheless there was lack of sufficient understanding about the hydrodynamic performance,the fluctuation of forces and the flow field characteristics of this propulsion system.The study of surface piercing propeller mainly depended on the hydrodynamic experiments.However,the experiments were limited by many factors,such as high cost and difficult operations.Although researchers have made some progresses on the theory studies,the mature theory was lack to guide the design of surface piercing propeller.The rapid development of CFD method made it possible to do the research of it.The numerical simulation of the standard model,841-B,was carried out.The flow field of surface piercing propeller was solved through Reynolds Averaged Navier-Stokes equation(RANS).The VOF(Volume of Fluid)method was used to capture the free surface.The sliding mesh technique was utilized to simulate the rotation of the propeller.The conclusions show that the numerical results are in good agreement with experimental data.The errors of hydrodynamic cofficients(thrust coefficient and torque coefficient)are less than 10%,and the transition zone gets obtained.These proved the CFD method was feasible to predict the performance of surface piercing propeller.This numerical scheme is used to simulate the surface piercing propeller installed on the planning boat.It studies the influences of the immersion ratio and the angle of oblique flow on the hydrodynamic performance of the propeller and analyzes the fluctuation of forces and the flow field characteristics.The conclusions show that with the immersion ratios increasing,the fluctuation of forces dereases.In the wake field,slipstream plays a decesive role,and the distinct slip-flow boundary occurs in the radial direction.Below the free surface,the axial velocity gradient is larger and the transverse velocity increases obviously.Above the free surface,the velocity in the axial and transverse direction increases significantly,but the slip-flow boundary is ambiguous.With the free surface as the boundary,the transverse velocity changes significantly.The angle of oblique flow affects the hydrodynamic performance very slightly.The reason is that the increasement of the immersion is very little due to the presence of the angle.When the immersion ratio increases,the torque of the propeller will increase rapidly.Then the vent pipes will be adopted to reduce it.So it studies the effects of different parameters of vent pipes,such as diameters,radial and longitudinal positions of the outlet,on the hydrodynamic performance through the numerical method.The results show that as the diameter of vent pipe increases,the thrust and the torque decrease and the efficiency increases at low advance coefficient.The radial and longitudinal positions of the vent pipes have a great influence to hydrodynamic performance at low advance coefficient.The diameters affect the ventilation volume,while the longitudinal and radial positions of the outlet mainly influence the suction effect of surface piercing propeller on the air.The numerical methods presented in this paper provide references for the further study on the hydrodynamic performance of surface piercing propeller.And the results are helpful to guide the practical engineering applications.