紧耦合气雾化流场结构突变过程的数值模拟

Numerical study on abrupt change of flow field in close-coupled gas atomization

紧耦合气雾化制粉过程中,当雾化气压超过某一临界值时,直管环缝型喷嘴的气雾化流场结构存在"开涡—闭涡"突变现象,雾化效果随之发生显著改变。该文采用数值模拟方法研究紧耦合喷嘴气体流场中开涡和闭涡结构特征及其突变行为,以及雾化介质类型和喷嘴几何结构参数(喷射顶角、导液管伸出长度和末端直径、环缝宽度)对临界雾化压力Pc的影响。结果表明:当雾化压力P略高于Pc时,马赫盘迅速截断回流区,流场结构由开涡向闭涡突变,并引起喷嘴熔体出口下方抽吸压力Pa骤降,突变前后抽吸压力差ΔPa约为30 kPa;雾化介质类型和喷嘴主要几何结构参数对Pc有显著影响,但对ΔPa无明显影响。

Using numerical simulation,the gas dynamics of the open-wake and closed-wake conditions of an annular-slit close-coupled gas atomization were investigated.The effects of gas type and nozzle geometry parameters including the apex angle,the protrusion length and the melt tip diameter of the liquid pipe as well as the annular slit width on the critical pressure Pc were discussed.The results show that open wake abruptly shifts to close wake,a bow Mach disk forms and truncates the recirculation zone and a sudden drop of aspiration pressure Pa with a variation of ΔPa about 30 kPa will happen when atomiing pressure of P slightly above Pc.The gas type and nozzle geometry parameters have great influences on the critical atomizing pressure of pc,while they have marginal influences on ΔPa.