超声射流系统设计及仿真分析

Simulation analysis and design of ultrasonic jet system

为了改善超快激光的加工效果,设计了超声气体射流系统。通过超声与射流的耦合可实现声能与射流压力能叠加,增强射流的脉动性,形成脉动射流。以氮气为传递介质,利用FLUENT软件研究了在稳态条件下不同喷头结构的流场分布并对喷头结构进行优化;在瞬态湍流状态下,运用动网格技术将超声与射流场耦合,仿真分析了超声振动参数对流场分布的影响以及各参数间相互作用规律。仿真结果表明:在超声频率20 kHz、幅值为20μm、进口流速2 mm/s条件下,流场最大流速从4.01 mm/s增至21.19 mm/s,随入口流速增加出口流速增幅逐渐下降,在高速射流入口条件下,出口最大流速也增加近两倍左右。在超声作用下射流脉动性显著增强,但射流流束的集中性会减弱,超声振幅的改变只能对射流场结构产生改变,对射流最大流速几乎无影响,超声频率的增加可提高流场最大流速及其脉动性。

In order to improve the machining effect of ultra-fast laser,an ultrasonic gas jet system was designed.Through the coupling of ultrasonic and jet,the superposition of sound energy and jet pressure energy can be realized,and the pulsation of jet can be enhanced to form pulsation jet.Taking nitrogen as the transfer medium,FLUENT was used to study the flow field distribution of different nozzle structures under steady state conditions and optimize the nozzle structure.In the transient turbulent state,the ultrasonic and jet fields were coupled with the dynamic grid technology,and the influence of ultrasonic vibration parameters on the flow field distribution and the interaction law of parameters were simulated and analyzed.Simulation results show that under the ultrasonic frequency of 20 kHz,amplitude of 20μm and inlet flow speed of 2 mm/s,the maximum flow rate increases from 4.01 mm/s to 21.19 mm/s,and the increase of outlet flow rate decreases gradually with the increase of inlet flow speed.However,under the condition of high-speed jet inlet,the maximum flow speed at outlet increases nearly twice.Furthermore,the double fluid pulsation was significantly enhanced under ultrasound,but the concentration of jet flow beam is weakened,ultrasonic amplitude changes can only change the jet flow field structure,but has almost no effect on the biggest jet velocity.The increase of ultrasonic frequency can improve the maximum velocity and pulsation of the flow field.