Binary Bionic Coupling Research On Water-solid Interface System For Drag Reduction

The resistance of biological and artificial craft in water is about800times the airresistance, apparently moving objects in the water need to consume more energy toovercome the resistance caused by the viscosity of water. The drag form is divided into threetypes: friction, pressure drag and wave resistance. The friction resistance is the main part,account for about40-80%of the total resistance. thus, reducing the friction drag can reducethe resistance of the moving body navigation significantly, reduce energy consumption,reduce pollutant emissions.Most artificial craft increase speed by increasing power, not only increases energyconsumption but also increase emissions. Aquatic organisms especially fish, body structure,shape, materials and movement mechanisms and other features formed by the longevolutionary, can effectively reduce the swimming resistance. Scale morphology, surfacemucus, swimming way, shape causes resistance decreased.The bionic mucus groove was designed based on scale geometry and the shearcharacteristics of fish mucus. The drag reduction on bionic mucus and bionic groove andcoupling are researched, by using of numerical simulation and flume experiment method.The morphological of fish scales were tested and analyzed, the geometric parameters ofscales and arrangement was obtained. The model of fish scales shape and arrangement wasestablished. Scale films is oval, the front zone of scale embedded fish skin, rear area wassuspended state, full of mucus between scales and epidermis.Using the geometric parameters of scales and arrangement, the form of scale films wasabstracted into the groove structure, the three-dimensional geometric model was established,the groove width is of1-5mm, the groove depth is of0.1-0.5mm, the groove spanwisedirection is at a90degree angle with the flow.The distribution of fish mucus is non-uniform, from head to tail, the content showing agradual decreasing trend. The content of mucus on catfish and snakehead are higher than thatof grass carp and carp.The shear behavior of the fish mucus was tested and analysised, theviscosity of mucus decreases as the shear rate increased, showed pseudoplasticity shearproperties. The viscosity of mucus on catfish and snakehead is higher than that of grass carpand carp. The shear characteristics of mucus aqueous solution amount of5-15g/L was tested and analysised, the viscosity of the solution was still pseudoplasticity, decreasesing asthe shear rate increasing. The viscosity of fishbowl was tested, the results shows nosignificant difference with pure water, that Indicates that fish mucus is attached to the bodysurface, almost insoluble in water environment.The behavior of mucus on fish was simulated, using the method of composite withsilica powder adsorption and porous materials. The10-30min. release tests showed thatcomposite method of porous and silica can slowly release polyacrylamide. to thesolution.The method of porous material release, is capable of simulating the state of fishmucus, formed mucus at the liquid-solid interface layer.The resistance characteristics of groove was studied by numerical simulation method.The relevance of groove parameters and resistance was study by orthogonalexperimental design method. The effects of cross-sectional form of the groove and thegroove width and groove depth factor on drag reduction was researched. The simulationresults show that the depth and width of the groove is a key factor affecting drag reduction,the greater the depth of the groove drag reduction effect is better. At the same depth, thegroove width is smaller the drag reduction effect is better. The groove depth and width wasoptimized further, the drag reduction rate increased with increasing of groove depth as thewidth is fixed. As groove depth high ratio exceeds0.5, the drag reduction rate of increase isslowing down, the maximum drag reduction rate reach of52%under simulated conditions.The drag resistance on polymer additives was studied by numerical simulation. The dragresistance will be reduceing as the concentrations of polymer additive becomes Lower or theshear rate becomes higher.The maximum drag reduction under simulated conditions reached26%. When the speedis less than6ms-1, the solution of polymer additives that concentration is of3.8g/L occursphenomenon that resistance increased, the same to the solution that the concentration is of2.3g/L, When the speed is less than2ms-1.This is because the low speed winding curlinglong-chain molecules are not fully extended, impede fluid movement, resulting in theresistance increases.According coupling bionics, combining the optimized groove parameters and theappropriate concentration of polymer additives, numerical simulate the drag reductioncharacteristics of the coupled behavior. The numerical analysis results show that the dragreduction rate can increase further with optimized bionic coupling parameters. The dragreduction effect of Polymer additives can be produced, when the flow exceed a certain speed and in the appropriate concentration.When the speed is lower than the critical value, thelong-chain polymers do not stretch fully, in this case,not only decrease the drag reduction,but also increase the resistance.The flume experiment results showed that the groove depth and width are the significantfactors affecting the frictional resistance. The friction increases as the groove width increases,the friction decreases as the groove depth increases.Drag reduction rate increased with increasing of the depth of the grooves, at a depthmore than0.5times the width, the increase rate of drag reduction slowdown. Drag reductionrate is also associated with the fluid velocity, drag reduction rate increases as the flow rateincreases. The maximum drag reduction rate reached42percent in flow velocity is10ms-1and the groove depth is0.8mm. The friction of mucus bionic is about1.6powerassociated with velocity, The friction of non-bionic is about1.8power associated withvelocity. The exponential growth of the bionic sample decreased0.2. drag reduction rate ofbionic mucus increases with speed improve. the maximum drag reduction was28%at theflow speed is10ms-1. The drag of bionic mucus are decrease in all test speed range, it doesnot appear that to the resistance increase at low speed phenomenon by numerical simulation.drag reduction test on the groove structure and mucus were coupling bionic wasperformed, the results show that the rate of drag reduction of coupling bionic is higher thanthat the individual bionic under the test conditions. The drag reduction rate of bioniccoupling element is not equal to two separate simple superposition, the maximum dragreduction rate of coupling is approximately equal to80%of the summation by two separatecoupling element. The coupled drag reduction rate is not less than any one of the couplingelement alone, The maximum rate of drag reduction on bionic mucus reach28%,themaximum rate of drag reduction on groove reach42%,the maximum rate of drag reductionon coupling reached58%.