Parametric Study Of The Traveling Wave Motion In Energy Absorption Mode

Fish have mastered superb swimming skills after a long period of natural evolution.Among them,most fish do work to the environment through the traveling wave motion of their bodies to obtain forward thrust and realize propulsion.It is called traveling wave propulsion.Our research group found that under certain motion parameters,the traveling wave motion body can absorb energy from the incoming flow.This means that there are two modes of traveling wave motion: propulsion mode and energy absorption mode.This new energy absorption method that imitates the traveling wave motion of fish is called traveling wave energy absorption.In this paper,a two-dimensional numerical simulation of the flexible traveling wave plate that is undulating in the wind is carried out using computational fluid dynamics software.The influence of geometric parameters and motion parameters on the traveling wave energy absorption characteristics is systematically studied,and the mechanism of the traveling wave energy absorption and the influence mechanism of each parameter on its energy absorption characteristics are revealed.The main content of this thesis is as follows.First,referring to the model experiment of fish traveling wave propulsion,the numerical simulation of the flow around the airfoil with traveling wave motion is carried out.And the simulation results are compared with the experimental results in the literature to confirm that the numerical calculation method used in the research is reliable.On the other hand,the grid independence verifications and time step convergence verifications of the computational model used in the study are carried out,and it is confirmed that the computational model used in the study is also reliable in terms of computational accuracy.Secondly,two similar waveforms,that is,two waveforms with equal dimensionless amplitude,are selected for calculation and comparison under the same working conditions.It is found that their energy absorption efficiency is equal and the flow field structure is similar,which indicates that the dimensionless amplitude can accurately describe the transverse geometric characteristics of the traveling wave waveform.On this basis,a systematic single-factor parameterization research of the influencing factors of traveling wave energy absorption including dimensionless amplitude(waveform transverse geometry parameter),dimensionless wave speed(waveform motion parameter)and wavenumber(model flow direction parameter)is carried out.Within the parameters studied,the results show that:(1)For the single-waveform model,the energy absorption efficiency increases with the increase of the dimensionless amplitude of the waveform,but the growth rate gradually slows down.The energy absorption efficiency increases first and then decreases with the increase of the dimensionless wave speed.There is an optimal dimensionless wave speed so that the energy absorption efficiency can reach the maximum value under the corresponding dimensionless amplitude.For the waveforms with relatively small dimensionless amplitude,the optimal dimensionless wave velocity is 0.3,and for the waveform with relatively large dimensionless amplitude,the optimal dimensionless wave velocity is 0.5.In the range of parameters studied,when the dimensionless amplitude is 0.20 and the dimensionless wave velocity is 0.5,the energy absorption efficiency of the single waveform model reaches the maximum,about 41%.(2)When the dimensionless amplitude of the waveform is small,the energy absorption efficiency increases with the increase of the wavenumber and when the dimensionless amplitude of the waveform is large,the energy absorption efficiency first increases and then decreases with the increase of the wavenumber.There is an optimal wavenumber,which makes the traveling wave energy absorption efficiency reach the maximum value under the corresponding dimensionless amplitude.In the range of parameters studied,when the dimensionless amplitude is 0.12,the dimensionless wave velocity is 0.5 and the wave number is 2.5,the energy absorption efficiency of the multi waveform model reaches the maximum,which is about 59%.(3)For the multi-waveform model,similar to the single-waveform model,the energy absorption efficiency also shows a law of first increasing and then decreasing with the increase of the dimensionless wave speed.There is an optimal dimensionless wave speed that makes the energy absorption efficiency obtain the maximum value under the corresponding wavenumber.When the wavenumber is small,the optimal dimensionless wave speed is about 0.5;when the wavenumber is large,0.6 is the optimal dimensionless wave speed.Finally,the parameter optimization of traveling wave energy absorption characteristics based on response surface analysis(RSM)shows a good prediction effect on the energy absorption efficiency of traveling wave motion,and the influence laws of various factors on the energy absorption efficiency of traveling wave are given.The optimal combination of influencing factors and parameters based on the response surface analysis method is the dimensionless amplitude a=0.10,the dimensionless wave velocity c=0.50,and the number of waveforms n=8.0.At this time,the experimental value and the predicted value of the traveling wave energy absorption efficiency are respectively are61.22% and 55.35%,which are the maximum traveling wave energy absorption efficiencies within the studied parameter range.The specific conclusions are as follows:(1)Similar to the results of the single-factor parameterization study,it is found that the energy absorption efficiency of traveling wave motion increases first and then decreases with the increase of dimensionless wave speed.However,the response surface analysis further shows that this law does not have a relationship to do with the geometric characteristics of the traveling wave plate,that is,whether the waveform has small dimensionless amplitude or large dimensionless amplitude,and whether the model is composed of a single waveform or multiple waveforms.(2)In the range of the number of waveforms studied,when the dimensionless amplitude of the waveform is large,the energy absorption efficiency of the traveling wave plate decreases with the increase of the number of waveforms.And when the dimensionless amplitude of the waveform is small,the energy absorption efficiency of the traveling wave plate increases with the increase of the number of waveforms,which also makes the response surface analysis fail to give the parameter combination with the maximum energy absorption efficiency within the range of the studied parameters.At the same time,the efficient energy absorption range of single waveform and multiple waveforms downlink energy absorption is summarized and its characteristics are analyzed,and the way to maximize the energy absorption efficiency of single waveform model and multiple waveforms model is revealed.It is found that for a single waveform model,the key to maximizing energy absorption efficiency lies in "balance".It includes two parts of balance.The medium dimensionless wave velocity balances the pressure gradient on both sides of the waveform and the lateral velocity vector of the waveform,so that the waveform has a large work ability;The medium dimensionless amplitude realizes the balance between the work ability of the traveling wave plate and the maximum energy that can be absorbed.For the model composed of multiple waveforms,the key is to realize the reasonable distribution of incoming energy on the waveforms.Through smaller dimensionless amplitude and larger dimensionless wave velocity,the obstruction of the upstream waveform to the incoming flow is weakened,so as to avoid too many parts of the incoming flow flowing around both sides of the waveform,retain most of the incoming flow energy at the sweep height of the waveform,and then use multiple waveforms to repeatedly absorb the incoming flow energy,so as to obtain a large energy absorption efficiency.And realize the utilization of the residual velocity of the incoming flow at the expense of the workability of a single waveform,so that the model gains high energy absorption efficiency as a whole.