Drag-reduction Mechanism Of Thermally Conductive Elastic Bionic Wall Based On The Method Of Fluid–Structure–Heat Coupling

Studies have shown that some warm blood creatures,such as dolphin,can use its surface elasticity and body surface temperature to actively control the fluid medium so as to achieve drag reduction.Based on the above phenomenon of biological coupling,the research team constructed and prepared a biomimetic functional surface with both elasticity and thermal conductivity.The surface can undergo regular deformation under the action of fluid,its energy dissipation in the deformation process will be manifested as heat,which will be transfer out relying on its thermal conductivity and heat the fluid boundary layer to reduce resistant.There are complex multiphysics couplings between the surface and fluid during the working process,the couplings mainly includes that the coupling of the flow field state and the solid boundary,the coupling of the solid deformation and the surface temperature increase,the coupling of surface deformation and temperature and fluid medium.In order to investigate the highly non-linear and complex coupling of bionic functional surfaces,a three-field coupling model of stress-strain-temperature between thermally conductive elastic bionic wall(TEW)and fluid medium was established.To study the relationship of stress-strain between TEW and flow field,this paper used bidirectional fluid-structure coupling research method with ANSYS + CFX to simulate the flow of TEW and rigid wall in the channel under different inlet velocity conditions.The comparisons of near-wall fluid velocity,eddy viscosity,turbulent flow dissipation,and turbulent kinetic energy of TEW and rigid wall were performed,and drag reduction rates of pressure difference was calculated.For the study of TEW strain-temperature relationship,the variable data was imported into ANSYS software and the temperature field of TEW was numerically simulated and analyzed.The relationship among the surface temperature rise of TEW,flow rate and elastic modulus was studied.As to study the effect of TEW surface temperature and strain on fluid medium,the two-way fluid-structure coupling between the TEW and the fluid medium was calculated under the condition of temperature rise of the wall,and the effects of wall temperature difference,fluid temperature and fluid velocity on the fluid medium were studied.The result of the study of stress-strain between TEW and flow field shows that nearwall fluid velocity of TEW is larger than rigid wall,but the near-wall fluid eddy viscosity,turbulent flow dissipation,and turbulent kinetic energy of TEW are all smaller than rigid wall.The TEW can react rapidly to the disturbance of the fluid medium,and use its elastic deformation to suppress the disturbance of the fluid,thus achieving the function of stabilizing fluid medium.This paper carried out drag reduction rates calculation of TEW with different elastic modulus under different flow velocity of 1 m/s,3 m/s,6 m/s and 12 m/s,and made a comparative analysis with the rigid wall surface.The results shows that drag reduction effect of TEW is correlated with flow velocity,there is no drag reduction effect when flow velocity is 1 m/s due to its the micro deformation;the maximal reduction rate is 7.55 % when velocity is 6 m/s and the elastic modulus of TEW is 0.05 Mpa;but when the velocity is 12 m/s,the drag reduction effect of TEW is not obvious.What is more,the drag reduction effect of TEW is also related to elastic modulus of TEW,there is an optimum elastic modulus for each flow velocity,in which the drag reduction rate is maximum.The paper analyses the drag reduction mechanism of TEW from the point of near-wall velocity gradient,finding out that TEW in the fluid medium can reduce the thickness of near-wall viscous layer and transition layer using its wavy deformation,improving the efficiency of the whole fluid flow,increasing the near-wall velocity,so as to realize drag reduction.The result of the study of TEW strain-temperature relationship indicates that the peak temperature rise and surface temperature of TEW have correlation with elastic modulus and flow velocity.The larger the flow velocity and the smaller the elastic modulus of TEW(the larger the deformation),the heat generated by deformation of TEW is higher,and the surface temperature is greater.However,the highest TEW surface temperature rise is less than 0.5 ? relative to the initial setting temperature 20 ?.The result is just a reference for studying the effect of TEW surface temperature and strain on fluid medium.The simulation analysis of the effect of TEW surface temperature and strain on fluid medium shows that the drag reduction effect of TEW has positive correlation with fluid temperature and wall temperature difference.For the flow velocity,it shows that the smaller velocity will have a better drag reduction effect because of more time for heat transfer between TEW and fluid medium.In addition,the effect of flow velocity on TEW is dynamic,and the heat transfer between the fluid and the wall is determined by the combination of heat transfer time and heat transfer area,but there is a strong negative correlation between heat transfer time and heat transfer area(surface deformation).This study reveals the mechanism of the surface/fluid media system of the elastic thermal conductive bionic function.This paper provides a new theoretical basis for the development of bionic drag reduction technology,and provides new ideas for the realization of the efficiency of fluid machinery.