Study On Propulsion And Energy Absorption Mechanism Of Typical Underwater Bionic Foils

In the nature,through natural selection over thousands of years,creatures are capable of swimming or flying in fluid medium such as air or water.Study on the propulsion modes of swimming or flying creatures has important significance to underwater propulsion.In the mechanical discipline,biomimetics has become a research focus.Moreover,biomimetics is of vital importance in underwater exploration,ocean exploitation,national security and other important domains.With the developments of technologies,different bionic propulsors have been successfully developed.Unfortunately,propulsion performance of these bionic propulsors can not achieve the same performance as biological prototypes,which highlights the necessity of further study on propulsion mechanism.The mechanism research plays important role,and will boost the developments of principle prototype.In order to reveal the mechanism of high-efficiency propulsion,scholars at home and abroad have devoted lots of efforts with different research methods.However,either the prototype-based experimental results,or numerical results are far from expected performance.Taking high-efficiency propulsor developments as the research background,the paper chooses typical foils as the research object and focuses on the propulsion mechanism of bionic foils and energy absorption mechanisms in complex flow field.To investigate the propulsion mechanism of bionic foils,the paper proposes a numerical method.Firstly,according to the biological observations,geometry model and kinematics model of bionic foils are established.For two-dimensional case,Immersed Boundary Method is adopted to solve the moving boundary problem,Lattice Boltzman Method and Finite Difference Method are adopted to solve the governing equations of fluid domain.For three-dimensional case,dyamic body-fitted mesh is adopted to solve the moving boundary problem,Finite Volume Method are adopted to solve the governing equations of fluid domain.Several numerical examples are carried out to verify the reliability of the numerical method adopted in the paper.Finally,experimental platform is designed and developed to provide further verification of numerical results.The proposed numerical method is used to carry out research on propulsion mechanism of NACA foils.The effects of stroke angle,amplitude of angle of attack,amplitude of heave motion and Strouhal number on the propulsion performance are respectively analyzed.Response Surface Methodology is used to analyze the comprehensive influence of these parameters and set up the mathematic model between motion parameters and propulsive performance.After that,the effect of spanwise flexibility on the propulsion performance is studied.By extracting the flow field characteristics in the wake,the hydrodynamics mechanism of these effects is analyzed further.The numerical results are verified by experiments.Considering the influence of three-dimensional shapes,the propulsion mechanism of crescent-shaped foils is studied.The effects of amplitude of angle of attack,amplitude of heave motion and Strouhal number on the propulsion performance are respectively analyzed.Response Surface Methodology is used to analyze the comprehensive influence of these parameters and set up the mathematic model between motion parameters and propulsive performance.After that,the effect of spanwise flexibility on the propulsion performance is studied.By extracting the flow field characteristics in the wake,the hydrodynamics mechanism of these effects is analyzed further.The numerical results are verified by experiments.In the nature,flow field environment is complex.Complicated drag reduction and energy absorption mechanism exist in animal swimming.Therefore,it is of great significance to study the propulsion mechanism of foils in complex flow field environment.Firstly,the coupling motion between flexible plate and rigid cylinder is numerical simulated,and the energy absorption mechanism is analyzed.In addition,the effects of space,mass ratio and Reynolds number are analyzed further.After that,motion and flow field characteristics of wave foil behind a rigid cylinder are studied.Finally,propulsion modes of NACA foils in tandem arrangement and thunniform bioinspired modes in tandem arrangement are studied respectively.To verify the reliabilities of geometry model and kinematics model adopted in the part,numerical simulations of thunniform bio-inspired mode are carried out,then velocity and flow field characteristics are analyzed.By extracting the flow field characteristics in the wake,the interaction modes and energy absorption mechanism are analyzed further.