Numerical Study Of Lateral Groove Flow Field And Analysis Of Drag Reduction Mechanism

The high speed of the underwater weapon system can help to initial the surprise of attacks.Power and drag reduction technique are required to achieving high speed.There are many kinds of drag reduction technique,and the groove treatment for drag reduction has the advantages of being easy to apply and without extra energy consumption,which is of great value for the development of underwater weapons.Presently,researches of longitudinal grooves were not as much as on lateral grooves.The present thesis work focused on the numerical analysis of the effect of lateral groove size,angle,number,spacing,and shape,and then analyze the mechanism of lateral groove drag reduction according to the research results.To begine with,pre-processing of domain selection and griding were made in favour of batch numerical simulations;considerations on selecting the turbulence model.boundary conditions、lateral groove parameters and solution methods,etc.were also optimised.Numerical simulation batch works of the drag reduction of the lateral trench under different parameters is performed.As a result,the numerical outputs weree analyzed and compared with respect to multiple angles of drag reduction rate,shear stress,velocity field,turbulent kinetic energy,vorticity,etc.,and the drag reduction mechanism of the lateral groove is summarized.The results revealed that(1)Under the same calculation conditions,the total resistance,shear stress,turbulent kinetic energy,and vorticity of the lateral groove wall are smaller than that under the circumstance of the smooth plate surface,and the lateral groove structure has a drag reduction effect.(2)The size,angle,number,spacing,and shape of the lateral grooves obtain the maximum drag reduction rate when s+=21,α=60° N=25,d=0.75s,and right zigzag.(3)The shear stress on the lateral groove wall is the frictional resistance.The shear stress increases with the increase of the groove size s+and the groove angle α.The shear stress decreases with the increase of the number of grooves N and the groove spacing d.It is the smallest when the groove shape is "V" shape,and the largest when it is rectangular.(4)Combined with the calculation results,the mechanism of drag reduction in lateral groove is analyzed from the aspects of drag reduction rate,near wall velocity field and boundary layer energy.From the angle of drag reduction rate,it is explained that the drag reduction is due to the difference between the decrease of friction resistance on the surface of lateral groove and the increase of pressure difference resistance;from the angle of near wall velocity field,it explains the theory of "protruding height difference" and "micro air bearing".From the point of view of boundary layer energy,it is explained that the energy consumption between the surface fluid and the wall of the lateral groove is smaller than that of the smooth plate surface,so the friction resistance is smaller.