Research On Drag Reduction In Flow Field By Multi Order Bending Mode

In recent years,the application area of AUV(autonomous underwater vehicle)has become wider,which draws the attention of many countries.The AUV whose structure looks like submarine or torpedo plays an important role in both military use and civilian use,such as explore,search and rescue,resource exploitation.But the resistance from water restricts the endurance ability of AUV hardly.By reducing drag,the endurance and the speed of AUV will be improved greatly and can be saved much energy.It provides people with high social and economic values.Darg reduction by vibration is a new way to reduce flow resistance in recent years.What makes it special is that it can reduce drag without change surface structure of vehicles.Methods of this article include mechanical oscillations,fluid dynamics,and piezoelectric theory.This article design the structure of AUV,stick the piezoelectric ceramics to the wall of AUV and make it vibrate.then theories of darg reduction was studied.The key point of this research includes the effects of darg reduction when the incident flow-surface and the back flow-surface are vibrating.To study the effect and principle of different vibration modes,we also made a comparation between effects of side face vibration and flow-surface,back flow-surface vibrations.This article firstly analyzes the boundary layer of flow field to get the relationship between friction drag coefficient and Reynolds number.Then The main content of the article is research the drag reduction effect of the third order bending vibration and the first order bending vibration by the turbulence of vortex structure and the separation of boundary layer.This article build the finite element model of AUV.Then making model analysis and transient analysis on AUV,from which the working frequency and the equation of wall vibration have been calibrated.The multi-Physics Coupling Simulation,which include fluid structure piezoelectric,has been made to correct the work frequent value of wet model.By leading the equation of wall vibration to the CFD software,setting the boundary conditions,and meshing the grids of boundary layer,the fluid-simulation analysis are build.The variable of simulation includes speed,length-width ratio,and phase position of vibration.Then making the contrast with vibration-free,calculating the value of drag and drag reduction efficiency to analyze the theory of drag reduction.Based on the theories and simulation results,we processed an experimental prototype and made the test of impedance characteristic and laser scanning,from which can get the working frequency and the amplitude of AUV.The results of experiment and simulation matched well.Experimental platform of flow field drag reduction was built to experimentalize the effect of drag reduction caused by different speeds,length-width ratios,and phase positions of vibrations.Then,we compared simulation and experimental results and analyzed the causes of the error.