液体横向射流在气膜作用下的破碎过程

Breakup process of liquid jet in gas film

为了研究液体横向射流在气膜作用下的破碎过程,采用背景光成像技术及VOF TO DPM方法进行了实验研究和仿真研究,模拟介质为水和空气.研究结果表明,液体射流在气膜作用下主要存在两种破碎过程:柱状破碎和表面破碎.Rayleigh-Taylor(R-T)不稳定性产生的表面波是液体射流发生柱状破碎的主要原因,气流穿透表面波的波谷导致射流柱破碎,破碎后的液丝沿流向逐渐发展呈带状分布.Kelvin-Helmholtz(K-H)不稳定性产生的表面波是液体射流发生表面破碎的主要原因,液丝和液滴从射流表面剥离.局部动量比对液体横向射流的破碎过程具有重要影响,当局部动量比较低时,液体射流的破碎由K-H不稳定性主导;随着局部动量比的增大液体射流的破碎逐渐由R-T不稳定性主导.液体射流的破碎长度及穿透深度均随局部动量比的增大而增大.

In order to study the breakup process of liquid jet in gas film,the backlit photography technique and the VOF TO DPM method are used for experimental and simulation research respectively.Water and air are used as simulant media.Grid adaptive technology is used to refine the gas-liquid interface grid and improve the capture accuracy of the gas-liquid interface.The results show that there are two main breakup processes of liquid jet in gas film:column breakup and surface breakup.The local high-pressure zone in front of the liquid jet makes the jet have a large normal velocity gradient,which causes R-T instability.The surface wave that is generated by the R-T instability is mainly responsible for the liquid column breakup.When the thin liquid film reaches a column breakup point,the airflow penetrating the trough of the surface wave causes the jet column to break.The tangential velocity gradient is generated when the gas film bypasses the liquid jet surface,which causes K-H instability.The K-H surface waves cause ligaments and droplets to strip from the surface of the liquid jet.The local momentum ratio has an important influence on the breakup process of the liquid jet in gas film.When the local momentum ratio is low,the breakup of liquid jet is dominated by the K-H instability.As the local momentum ratio increases,the breakup of liquid jet is gradually dominated by R-T instability.The local momentum ratio plays an important role in the distribution range of the liquid jet in gas film.When the local momentum ratio is low,the ligaments and droplets caused by the liquid jet are mainly distributed within the range of gas film.As the local momentum ratio increases,part of the ligaments and droplets escape from the range of the gas film.The liquid jet penetrates the gas film when the local momentum ratio is greater than 0.74.The breakup length and the penetration depth are both affected by the local momentum ratio.The breakup length increases with the local momentum ratio increasing.The penetration depth also increases with the local momentum ratio,and the penetration depth increases significantly when the liquid jet penetrates the gas film.