Study On Cavitation Effect Of Ultrasonic Control Of Nano-Particle Flow Technology

Conical micro-nano structures(such as atomic force microscope probes)have unique physical and chemical properties due to their extremely sharp tip structure.The probes will inevitably be contaminated and worn during use.It is difficult and expensive to process or repair them to maintain high shape and size accuracy.Therefore,the research group combines the abrasive flow machining technology with the ultrasonic physical effect,and proposes the ultrasonic-controlled nano-abrasive flow technology.In order to improve the technology and realize the controllable process,this paper studies the dynamic characteristics of microbubbles in the flow field under the action of ultrasound,the conditions of ultrasonic cavitation effect in the fluid,and the key factors affecting the cavitation effect and processing effect.The main contents of this paper are as follows :(1)The dynamic equation of a single microbubble under ultrasonic action is derived.The 4-5 order Runge-Kutta method combined with Matlab programming is used to numerically calculate the equation.The effects of different ultrasonic frequencies,ultrasonic amplitudes and initial radii of microbubbles on the dynamic behavior and cavitation effect of microbubbles are obtained.It is found that the larger the ultrasonic sound pressure and the closer the ultrasonic frequency to the natural frequency of the microbubble,the more likely the transient cavitation occurs.(2)Based on RNG k-ε turbulence model and Schnerr-Sauer cavitation model,a multiphase flow simulation model of AFM probe ultrasonic vibration is established.The boundary conditions of the model are determined and the grid independence is verified.The secondary development of Fluent software was carried out by UDF method.The ultrasonic vibration of the probe was controlled by dynamic mesh technology.The pressure,velocity,gas holdup and dynamic pressure of the fluid area near the probe tip at different times were monitored.The conditions of ultrasonic cavitation effect near the tip and the distribution of flow field near the tip were explored.(3)The multi-phase flow simulation model of AFM probe ultrasonic vibration with different wear degrees was established.The cavitation effect intensity,cavitation type and flow field distribution characteristics of the flow field near the tip under different processing conditions were explored.The influence of some key factors(tip angle,tip width,processing height,initial gas holdup)on cavitation effect and processing effect was explored.It was found that the flow field characteristics when the processing height was less than 0.3μm,the tip angle was greater than 90 °,and the tip width was in the range of 0.3 ～ 2.0μm were more conducive to the sharpening of the tip.(4)Based on the atomic force microscope equipment,an experimental platform was built.The conditions of cavitation effect and the influence of some key factors on cavitation effect and processing effect were investigated by experiments.It was found that the high frequency vibration of the probe in the suspension environment was more conducive to the sharpening of the probe than the low frequency,indicating that the ultrasonic cavitation phenomenon occurred during the high frequency vibration processing of the probe.The influence of key factors on the processing effect was consistent with the trend of the simulation results.