Exciting Vibration Technology From Airflow-induced Sound On A Small Vibration Piezoelectric Generator

With the rapid development of science and technology,the function of fuze has been greatly promoted from traditional mechanization towards the direction of agility and intelligent.Modern fuze is getting higher and higher requirement of power supply,it needs more power supplies,which are real time fast supply,high safety and long time storage.With the trend of fuze miniaturization,increasing function and more internal device,space for the power supply is limited.Therefore,the contradiction between small volume and high output energy of fuze power supply is rather prominent.This paper takes the fuze physical power supply as the research background.The excitation mechanism of airflow induced sound,response characteristics of acoustic vibration and generating performance of small vibration piezoelectric generator has been studied by using the combined research method of numerical simulation and experiment.Firstly,based on the previous research,which has been determined that the short inlet with uniform section annular gap has features of fast flow transition,fast flow field uniform,rectification apparently and faster uniformly distribution of velocity,the excitation method from airflow induced sound and sound-induced vibration is applied,and the excitation mechanism from airflow induced sound with nozzle-resonator system is designed.Based on N-S Equation and SST k-? turbulence model,the flow field numerical simulation model of excitation mechanism from airflow induced sound is established.Comparing the result of numerical simulation with experiment,the rationality of the simulation model is verified.Meanwhile,the simulation result shows that the pressure,at the end of the resonator,oscillates periodically.It can form a steady vibration source,which proves the feasibility of the excitation mechanism from airflow induced sound.Secondly,applied the established model,the flow field of the excitation mechanism with nozzle-resonator system is simulated.Through observing the distribution of pressure and velocity fluid flied in the excitation process,the excitation mechanism from airflow induced sound,under the mutual coupling among the stable jet,the wedge and the resonator,is studied.The velocity contours reveal the complex vortex shedding pattern at the wedge of the resonator;the pressure contours reveal the air compression and expansion process inside the resonator;and the relationship between the axial velocity and sound pressure shows a standing wave formed inside the resonator.Meanwhile,the generated sound frequency is captured by the acoustic modal frequency of the resonator,and it can jump to higher mode under high inflow velocity.The results verify the mechanism of edgetone generated by vortex shedding and the function of frequency capture and amplification by the excitation mechanism with nozzle-resonator system.Thirdly,the effect of parameters on the excitation mechanism from airflow induced sound is analyzed.Through further expeiment study,it is found that there are different effects of the length,the space and the annular gap on amplitude and frequency of the excitation force.The result shows short resonator can obtain high frequency and stable vibration signal with larger amplitude under high airflow velocity.The space and the annular gap exist a best threshold,otherwise it leads to tiny amplitude,even no vibration.Therefore,it must carefully control the space and the annular gap when it is designed.In addition,combined with the effect of structure parameters on the excitation frequency,the experience formula of the acoustic modal frequency calculation,which is suitable for short resonator,is given.The theoretical calculation and the experimental result show the theoretical value is close to the experiment.Then,the vibration detecting device of airflow induced sound vibration piezoelectric generator is designed.The mass-spring-damper equivalent model based on the principle of vibration detection is established,and the expression of maximum mechanical output power of the vibration detecting device is derived.The working pattern of piezoelectric vibrator is analyzed,and the excitation pattern,the vibration mode and the fixing method of piezoelectric vibrator are confirmed.The forced vibration of piezoelectric vibrator is analyzed theoretically,and the vibration-electricity conversion model of piezoelectric vibrator is established.Finally,the performance of prototype of small airflow induced sound piezoelectric generator is tested,including excitation force characteristic and electricity generation performance of the prototype.The test shows a linear relationship between the excitation force amplitude and the airflow velocity,and the amplitude increases with the increase of the airflow velocity.The excitation force frequencies are stable and they are all around the first order acoustic modal frequency of the resonator,about 6 kHz,which shows the frequency amplified apparently.The relationship between amplitude and frequency of the output voltage along with the change of airflow velocity has the same form of the excitation force.The experimental prototype has relatively stable electricity generation capability.The output of maximum electric energy can reach 85.3 mW under the case of load matching.