低速同轴气流作用下空间发展液体射流的动力学
Dynamics of a spatially developing liquid jet with slower coaxial gas flow
摘要：
采用涡动力学（$λ_2$方法）对低速同轴气流中的三维圆形液体射流进行了数值模拟和解释。气液界面上的不稳定性很好地反映了界面附近的涡旋相互作用。某些关键特征是首次发现的。两种类型的表面变形的区别，这是由一个大的缺口上的射流杆分开：第一，那些附近的射流启动帽被封装在帽后面的回流区。这些变形与生长帽的动力学直接相关，并通过那里产生的涡旋很好地解释。第二，变形发生在更远的上游帽主要是由开尔文-亥姆霍兹（KH）不稳定性在界面处。三维变形首先发生在涡结构中，并且最初的轴对称KH涡变形并导致几个液体叶瓣，其首先作为薄化片拉伸，然后继续直接拉伸成细长的韧带-在较低的相对速度下-或者在较高的相对速度下拉伸以产生液体桥和孔。不同的方案取决于韦伯数和雷诺数的基础上的相对气液速度被发现在时间的研究。上游区域的变形在与液体射流的对流速度一起移动的框架中被很好地描绘。现在确定了时间分析的有用性。
英文摘要：
A three-dimensional round liquid jet within a low-speed coaxial gas flow is numerically simulated and explained via vortex dynamics ($λ_2$ method). The instabilities on the liquid-gas interface reflect well the vortex interactions around the interface. Certain key features are identified for the first time. Two types of surface deformations are distinguished, which are separated by a large indentation on the jet stem: First, those near the jet start-up cap are encapsulated inside the recirculation zone behind the cap. These deformations are directly related to the dynamics of the growing cap and well explained by the vortices generated there. Second, deformations occurring farther upstream of the cap are mainly driven by the Kelvin-Helmholtz (KH) instability at the interface. Three-dimensional deformations occur in the vortex structures first, and the initially axisymmetric KH vortices deform and lead to several liquid lobes, which stretch first as thinning sheets and then either continue stretching directly into elongated ligaments - at lower relative velocity - or perforate to create liquid bridges and holes - at higher relative velocity. The different scenarios depend on Weber and Reynolds numbers based on the relative gas-liquid velocity as was found in the temporal studies. The deformations in the upstream region are well portrayed in a frame moving with the convective velocity of the liquid jet. The usefulness of the temporal analyses are now established.
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