Research On Drag Reduction Performance And Flow Field Structure Of Bio-plate Inspired By Puffer Skin

In nature,the special structure of creatures can influence and control fluid flow to reduce drag and increase movement speed.Bionic drag reduction has become a hotspot of scholars all over the world,aiming to reduce frictional drag and increase movement speed to save energy consumption.In this thesis,puffer with migratory characteristics was used as the research object.Numerical simulation was used to study drag reduction performance of bio-plate inspired by puffer skin.The drag reduction mechanism of bionic puffer epidermal spines and mucus were further analyzed by the flow field structure.Research works were included within the following.Firstly,bionic puffer epidermal spines and mucus were selected as research objects,the calculation domain size,turbulence model selection and its feasibility verification,mesh generations,boundary conditions and drag reduction performance evaluation were set and designed.Secondly,the results of bionic puffer epidermal spines showed that as the bionic spinal height increased,the total drag reduction rate increased slowly to 19.5%,then significantly decreased.With the increase of the bionic spinal tilt angle,the total drag reduction rate maintained a relatively stable trend,reached 20.7%,and then showed a downward trend.The bionic spinal arrangement at the front end of the non-smooth surface was beneficial to increase the drag reduction performance.The puffer epidermal spines can achieve a more effective drag reduction effect along the inflow direction.The bionic spinal quantity of average arrangement was larger than that of staggered arrangement,so the drag reduction effect of the former was obviously better than that of the latter.With increasing arrangement quantity,the drag reduction effect was enhanced,but affected by the arrangement position,which weakened the drag reduction increments.With the increase of arrangement spacing,the drag reduction rate increased,and the drag reduction effect decreased after affected by arrangement position.More notably,the optimal drag reduction effect achieved by the arrangement parameters reached 23.1%.Thirdly,the results of puffer epidermal mucus showed that the apparent viscosity increased with increasing mucus concentration.And the apparent viscosity decreased with increasing shear rate,the mucus viscosity changed slightly and eventually stabilized when it reached a certain value.With increasing frequency,the storage modulus,loss modulus,and loss tangent accordingly increased.When the loss tangent value was less than 1,the elastic effect was greater than viscous effect;instead,the elastic effect was less than viscous effect.When the inflow velocity increased,and less than 0.1 m/s,the drag reduction effect increased;on the contrary,the drag reduction effect decreased.With increasing mucus concentration,when the inflow velocity was less than 0.2 m/s,the drag reduction increased;instead,the drag reduction decreased.It is worth noting that the optimal drag reduction effect of puffer epidermal mucus was 6.2%.Finally,the drag reduction characteristic of bionic puffer epidermal spines was determined by the difference between the viscous drag and the pressure drag.The drag reduction effect was achieved by the increment of viscous drag was greater than the increase of pressure drag.The pressure drag mainly came from the front row spines,reduced the front row pressure drag can effectively control the total pressure drag;The reverse vortex formed between the spines,impacted and separated,developed and merged to fill the space between the spines.The increase of low-speed fluid weakened the viscous drag.Besides,the rheological properties of puffer epidermal mucus played an important role in promoting the improvement of drag reduction performance.When the inflow velocity was constant,the viscoelasticity played a major role.When the inflow velocity increased,the wall drag increased,and the elastic effect was less than viscous effect,and the increase of wall drag was greater than the decrease of viscous caused by the fluid drag,which weakened the drag reduction performance of puffer epidermal mucus.