Research On Active Drag Reduction Technology Of Embedded Piezoelectric Vibration For Underwater Vehicle Wall

With the development of marine resources and facing the military requirements of rapid combat,miniaturized and lightweight underwater micro vehicles are gradually developed because they can respond to functional actions faster.However,the miniaturization of the underwater micro vehicle will reduce the size of the engine and the carried energy,resulting in the weakening of the driving power and the mileage.One of the most effective methods to improve the driving performance and endurance time of micro underwater vehicles is to reduce the friction drag of the wall during navigation.The existing underwater drag reducers can achieve good drag reduction performance,but they are not suitable for small underwater vehicles due to their large structure size and high energy consumption.In this work,a micro active drag reducer based on inverse piezoelectric effect,which can be embedded in the outer wall of the micro underwater vehicle without changing the streamline structure and structural strength of the outer wall,is proposed.It can achieve on-demand active drag reduction and effective energy saving,which can provide an important reference for the active drag reduction of the underwater micro vehicle.Firstly,this paper analyzes the drag reduction characteristics of the general arrangement angle of a single drag reducer.According to the small-area drag reduction requirements of micro underwater vehicles,a piezoelectric active drag reducer with spanwise arrangement is proposed.The characteristics of near-wall flow field and turbulence statistics are analyzed by multi physical field coupling simulation to reveal the drag reduction mechanism of piezoelectric drag reducer.The effects of the structural parameters,excitation signal parameters,sailing speed,the location of the drag reducer,etc.,on the characteristics of near-wall turbulent boundary layer are further studied.The selection methods of control parameters to meet different drag reduction requirements are proposed.The effective energy saving efficiency of the designed piezoelectric drag reducer are discussed.The experimental platform is built and the visualization experiment of particle image velocimetry for measuring friction drag are carried out.The influence of the piezoelectric drag reducer on the multi-scale coherent structure of near-wall turbulence are studied by using the wavelet transform method,and the drag reduction results are compared with the simulation results to verify the turbulent drag reduction effect of the designed miniature piezoelectric drag reducer with spanwise arrangement.Due to the different incoming flow directions at different positions of the micro underwater vehicle and the uncertainty of the navigation direction,this paper carries out the drag reduction performance analysis of the piezoelectric drag reducer with multi-angle arrangement based on the research of a single drag reducer with general arrangement angle.The influence of piezoelectric drag reducers with different arrangement angles on the drag reduction characteristics are discussed,and the influences of key parameters such as excitation signal,sailing speed,layout position of piezoelectric drag reducers,target drag reduction range on the turbulent characteristics are obtained.The control parameter selection methods to meet different drag reduction requirements are proposed.The experimental study on friction drag reduction of piezoelectric drag reducers with different arrangement angles are carried out.The turbulence statistical method which can reflect the drag reduction effect is used to analyze the experimental data.The simulation and experimental drag reduction results are compared to verify the effectiveness of the proposed arrangement and control method.Then,the total drag test experiments are implemented to prove the feasibility of high-efficiency active drag reduction of micro underwater vehicle based on the piezoelectric drag reducer.Based on the research of single drag reducer,the research on the cooperative drag reduction of multiple piezoelectric drag reducers are carried out,and a streamwise traveling wave drag reducer based on the cooperative work of multiple micro piezoelectric drag reducers is proposed,which can meet the large-area drag reduction requirements of micro underwater vehicle.Firstly,the methods for generating streamwise traveling waves in the near-wall turbulent boundary layer by arranging multiple piezoelectric drag reducers at intervals are presented.By analyzing the structure of near-wall turbulent flow field,the mechanism of achieving drag reduction by piezoelectric streamwise traveling wave drag reducer are revealed.The simulation methods are used to analyze the influence of the streamwise traveling wave drag reducer on the drag reduction performances under different traveling wave parameters,sailing speed,target surface position range,and the selection method of control parameters to meet different drag reduction requirements are proposed.The experimental study of friction drag is carried out,and the changes of average streamwise velocity profile,turbulence intensity and weighted joint probability density function distribution,when the traveling wave drag reducer works,are analyzed.Then,the experiment results are compared with the friction drag reduction results obtained by simulation to verify the correctness of the simulation analysis results.Experimental research for testing the total drag of the experimental prototype are carried out.The relationship between driving energy consumption and drag reduction performance of the traveling wave piezoelectric drag reducer is established,and the control parameter selection method to achieve high-efficiency energy saving and drag reduction are given.Finally,the research on the drag reduction characteristics of piezoelectric drag reducer with different traveling wave propagation angles are carried out in view of the actual working conditions of the micro underwater vehicle with irregular changes in the navigation direction and the need to achieve large-area drag reduction with traveling wave.The motion equations of traveling wave with different propogation directions are given.Then,the structural changes of turbulent boundary layer flow field caused by the actuation of piezoelectric drag reducers with different traveling wave propagation angles are analyzed,and the drag reduction mechanism of the drag reducers with different traveling wave propagation angles are revealed.Then,the influence of the traveling wave propagation angle on the drag reduction performance are studied through the simulation analysis method,and the relationships of the traveling wave parameters,sailing speed,layout position and action range on the drag reduction performance under each traveling wave angle are obtained.The control parameter selection methods to realize the high-efficiency drag reduction demand under different traveling wave propagation angles are given.The friction drag and total drag experiments are carried out to verify the effectiveness of the proposed drag reducers with different traveling wave propagation angles.The energy saving efficiency of piezoelectric drag reducers with different traveling wave propagation angles are analyzed.