| Solid-liquid separation is widely used in daily life and practical engineering,such as sewage treatment,beverage purification,oil separation,medicine preparation,etc.Traditional industrial filters are often clogged and damaged because they cannot be cleaned or replaced in time.Filter-feeders,on the other hand,are rarely clogged.Among these filter feeders,balaenid whales have gigantic bodies but they feed on aggregations of tiny calanoid copepods,which has special bionic applications and significances.According to the principle of function correlation,a mathematical model from the filter feeding behavior of balaenid whales is firstly abstracted and established,and the flow field and particle information of the hydrodynamic filtration system of balaenid whales are modeled and analyzed respectively.Then,the computational fluid dynamics(CFD)and discrete element method(DEM)coupled simulation model are used for further refinement where the effects of particle space and shape,as well as particle-particle/wall interaction are considered.On this basis,a new bionic filter inspired by the filter feeding of balaenid whales is designed by 3D printing and manufacturing.In this study,the biomechanical and hydrodynamic mechanisms involved in the filter feeding process of balaenid whales are explored,and then a bionic filter is designed inspired by the filter feeding of balaenid whales,which preliminarily realizes the bionic application from biological model to engineering design.The main researches of this paper are as follows:(1)A theoretical model suitable for the mouth characteristics of balaenid whales is established by combining the mass conservation and momentum conservation equations of APT branching flow and the APL combining flow,as well as the pressure drop equation of IB channel where the fringes layer is considered.The model corrects the effect of inconsistent shunt coefficients where the inertial and friction terms are both considered.The morphological characteristics of balaenid whales and fluid physics can be effectively correlated.(2)A discrete method using section-by-section calculation is used to solve the theoretical model,in which variable pressure recovery coefficient and friction coefficient apply,and then the flow field information including the the flow distribution and pressure drop in balaenid whale feeding are analyzed.This is a straightforward,easy-to-use and efficient calculation method.The flow distribution and the pressure drop both show increasing trends with the flow direction.The large APT channel width,small Reynolds number of entrance and small fringe layer permeability can contribute to emerge a good flow pattern with a smoother flow speed near the oropharynx,better drainage,better shunting and filtration,and higher energy efficiency.However,for the small width ratio of the APT channel to that the APL channel,some energy efficiency is sacrificed to achieve additional average transverse flow in order to produce better shunting and filtration.The research results can provide theoretical guide for the design of bionic filter channel.(3)The appropriate velocity profiles in the X and Y directions are adopted to approximate the flow field in the APT channel.Considering the coupling effect of particles,the force equations of particles in the flow field are solved by the four-stage Runge-Kutta method,and then the particle information including the particle trajectories and the filter cake profiles in balaenid whale feeding are analyzed.The particle trajectories consist of a series of backward-outward arcs and the particles tend to accumulate in the posterior region of the oral cavity.The small APT channel width and large fringe layer permeability make the tendency of particle posterior aggregation obviously.But the change in particle diameter has less influence on this tendency.The results further reveal the biomechanical mechanism and hydrodynamic law related to filter feeding of balaenid whales.(4)Considering the effects of particle space and shape,as well as particleparticle/wall interaction,the CFD-DEM coupled simulation model is adopted to further investigate the filtering mechanism in balaenid whale feeding.In this model,DEM is used for the particle and the Navier-Stokes equation is used for the fluid.The model is validated by comparing some crucial fluid and particle information with the theoretical results above.The large fringe layer permeability,random incidence direction,large particle diameter and real irregular shape all lead to more particle collisions.Besides,the large fringe layer permeability and particle diameter make the trend of posterior aggregation more obvious.However,there are no significant differences in the number of the captured prey at each location for different types of incident directions or prey shapes.The study further provides a new inspiration for the design of bionic filter.(5)Inspired by the filter feeding mechanism of balaenid whales and considering the local grooves in the fringes layer,a new bionic filter is produced by 3D printing technology through the bionic design of the Z-shaped channel inside the mouth of balaenid whales.At the same time,a test platform composed of the bionic filter,peristaltic pump,fluid pulse rectifier and water tank is built to carry out the fluid flow pattern dyeing nd particle filtration experiments.It is found that fluid separation occurs near the groove structure and local vortices are generated.The vortex filtration mechanism makes the particles in the front grooves tend to accumulate on the left side,which has a certain anti-clogging effect.Moreover,the increase of flow velocity leads to the enhancement of vortices,which makes the accumulation effect on the left more obvious.This study initially practices the bionic application from biological model to engineering design,and the vortex anti-clogging filtration mechanism proposed in the study has a wide range of application prospects and values. |
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