不定原点喷嘴射流中流体物理的实验研究

为了能够更好地了解不定源喷嘴（indeterminate origin nozzle）射流中的物理过程，本文应用平面激光诱导荧光技术对一个大尺度的水射流进行了实验研究。流场显示的实验结果表明不定源喷嘴在射流的剪切层引入了蘑菇形反向旋转的涡对。这些涡的矢量方向与射流方向相同或相反，被称为流向涡（streamwise vortex）。由于射流中存在开尔文一亥姆霍兹不稳定，每当一个横向涡（spanwisevortex，即涡的矢量方向与射流方向垂直）从喷嘴脱流时会产生瞬时的低压，该瞬时低压促使向内发展的流向涡对在喷嘴的凹槽处生成。这些涡对在向下游流动的过程中会重组并在喷嘴的尖峰面生成向外发展的涡对。这些流向涡极大地影响了射流的发展。流向涡与横向涡的相互作用促使射流更早地发展成为湍流。由于流向涡同时也在射流中引入了径向的剪切流动，因此导致了更多的湍流生成从而增强了射流与周围流体的混合。

Experimental Investigation of Flow Physics in Indeterminate Origin Nozzle Jet

In order to achieve better understanding of the physics underlying the indeterminate origin (IO) nozzle jet, an experimental investigation in a large-scale water jet was performed using Planner Laser Induced Fluorescence (PLIF) technique. Flow visualization results showed that IO nozzles introduced mushroom shaped, counter rotating streamwise vortex pairs into the jet shear layer. "Incursion" streamwise vortex pairs were generated at the IO nozzle valley locations as each braid region was shed from the nozzle, i.e. they were formed periodically during the K-H shedding processes. When propagating downstream, the incursion streamwise vortices reorganized with each other to form "excursion" streamwise vortex pairs at the IO nozzle peak locations. Streamwise vortices greatly influenced the evolution of the IO nozzle jet. Interaction between streamwise and spanwise vortices promoted earlier turbulence transition. Streamwise vortices introduced radial shear flow into the jet, which facilitated extra turbulence production and enhanced mixing between the jet and ambient fluids.