Flow Field Control And Drag Reduction Performance Study Of Bionic Shark’s Breathing Process

Currently,the friction resistance of the surface ships and underwater bodies is necessary to be reduced during the voyage,which is of great significance to improve the speed,range and saving energy,etc.Hence,a large amount of theoretical analysis and experimental research of the drag reduction in turbulent boundary layer are put forward,and some drag reduction methods are also presented,such as,the smooth surface,smooth wall,and the super hydrophobic,etc.However,due to various reasons,it has not obtained a wide range in the engineering practice.According to the inspiration of the shark’s breathing process,in this manuscript,the outside branchial cleft squirt water process of the shark breathing was simplified into the lateral jet process of the cross flow.Studies of the lateral jet process found that when the jet velocity is very small,the jet was enclosed within the boundary layer,which made the increasing thickness of the boundary layer increases to get the effect of the drag reduction effect.Thus,a jet surface drag reduction method imitating the breathe process of the shark gills is provided,and the method is achieved the goal of drag reduction by changing the flow field configuration of the boundary layer.In fact,study of the flow field structure of the turbulent boundary layer has important significance for realizing the control of the flow field of the boundary layer and improving the theory of the boundary layer theory.Fluid drag reduction research in the field of the hypersonic aircraft drag reduction is very common,which gained a remarkable drag reduction effect.However,with the complex underwater environment,whether the conclusions of the jet drag reduction achieved in the hypersonic field is suit to be apply in the underwater environment needs to be further studied.Subsequently,the jet surface model of bionic shark gills breathing process was built,and the numerical simulation was carried on.And the validity of the numerical simulation results were verified.After the experimental observation for the whitespotted smoothhound surface and gill opening structure parameters,the main factors influencing the shark gills breathing process was gained.With some simplifications of bionic shark gills breathing process,such as,the sharks around outside branchial cleft surface structure into the flat structure,the outer gill opening into the jet hole in front,and the shark’s breathing process into a continuous jet process,a jet surface model was established,and the numerical simulation are carried on.Using two methods of the experience formula and the experimental data,the effectiveness of the results of numerical simulation results were compared to demonstrate.Then,the performance of bionic jet surface drag reduction performance was researched.The drag reduction rate,the energy saving rate,and the energy efficiency formula were established,which was used to evaluate bionic jet surface drag reduction and the energy saving effect.The drag reduction performance of the size parameters of the jet hole,the hole shape and number of jet hole in different flow field were investigated.The results showed that under a constant of the jet hole area,the better flow drag reduction effect presented,when the ratio of the jet hole along the length of the exhibition to and the flow length,the jet velocity and the jet flow,exhibited a bigger value.Also,the circular jet hole behaved a perfect drag reduction effect,and with the increase of the jet velocity,the drag reduction rate increased gradually.When the arc radius was 4 mm,the drag reduction effect was best,and the maximum rate of the drag reduction was 9.51%.When flow rate were fixed,the drag reduction showed no change under the changing of the mainstream velocity and the jet velocity.It illustrated the velocity ratio is the main factors influencing the effect of drag reduction,the drag reduction effect was enhanced with the increase of the jet hole number.Also,the drag reduction effects on various jet parameters and the jet of factors were studied.The main jet parameters of single,double and revolution jet surface model were carried on a numerical simulation of the orthogonal optimization.It depicted that the shape factor k of a single jet hole has the largest effect on the drag reduction rate and the energy saving rate.When other factors were constant,the drag reduction rate and was linear increasing with the shape factors,and energy saving rate was parabola increasing with shape factors.The width of double holes jet flow surface on drag reduction effect was most affected,and jet velocity second.When other factors were constant,the jet hole width,jet velocity and drag reduction rate behaved a linear relationship.Annular jet body had an obvious effect on drag reduction and the energy saving,and the largest energy efficiency was 262,which was between "wall" and "smart skin".The drag reduction mechanism of bionic jet surface were discussed.After the numerical simulation of the flow field form in bionic jet surface boundary layer,the wall shear stress nephogram,the compressive stress contours,and the velocity contours of the smooth surface and the jet surface,the same section of the dimensionless velocity distribution curve,and the surface normal direction of the velocity gradient distribution were gained.Through the comparison and analysis,the drag reduction mechanisms based on increasing heart rate turbulence effect,the wall isolation effect,and the turbulent damping effect were proposed.Through the study of the flow field structure of the slender body,it found that the jet was blocked within the boundary layer,which supplemented the bottom fluid of the slender body,and delayed the boundary layer separation point to increase the range of back flow area.Also,the long length of recirculation region trail showed that wake of slender body of the low pressure center kept away from the its rear surface,which reduced the pressure resistance of the rear surface of the slender body.As a result,the drag reduction mechanism based on the increase of the static pressure effect of the bottom slender body was put forward.Finally,the jet fluid friction resistance on the surface was tested by the fluid friction resistance test experiment platform.Through comparing with the smooth surface,it discovered that bionic jet surface had the drag reduction effect.The drag reduction rate increased gradually with the increase of jet velocity,and the drag reduction rate ’decreased with the increase of the mainstream velocity.And the larger velocity ratio and the jet hole shape scale factor k presented a better the effect of drag reduction.Compared with the results of numerical simulation,the validity of the numerical simulation results was finally verified.