The effect of the exit geometry of a vortex ring generator was studied experimentally. Two types of exit geometries were chosen: an orifice and a nozzle. Vortex rings were generated by pushing a solenoid-valve-controlled, pressurized-air jet through the circular opening of the orifice or nozzle. Experiments were performed over a wide range of initial Reynolds number (450≤Re≤4580) and length-to-diameter ratio (0.7≤L/D≤7.0) of the air jet. The exit geometry was found to significantly influence the entire course of propagation of the vortex ring. The orifice-generated vortex ring had superior characteristics to that produced by the nozzle under the same conditions. The vorticity generated along the wall in the orifice exit plane had a negligible effect on the circulation of the vortex ring within the specified range of Reynolds number. Compared to the nozzle-generated vortex ring, the orifice-generated ring showed reduced initial vorticity losses and less diffusive entrainment of ambient fluid. The vortex rings produced by the orifice attained more circulation, less entrainment of ambient fluid and hence rapidly propagated through longer distances in comparison to the nozzle-generated rings.

中文翻译：

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空气中孔口和喷嘴产生的涡环的传播

通过实验研究了涡环发生器出口几何形状的影响。选择了两种出口几何形状：孔口和喷嘴。涡环是通过推动电磁阀控制的加压空气射流穿过孔口或喷嘴的圆形开口而产生的。实验在空气射流的初始雷诺数 (450≤Re≤4580) 和长径比 (0.7≤L/D≤7.0) 的大范围内进行。发现出口几何形状显着影响涡环的整个传播过程。在相同条件下，孔口产生的涡环比喷嘴产生的涡环具有更好的特性。在规定的雷诺数范围内，孔口出口平面沿壁产生的涡量对涡环环流的影响可以忽略不计。与喷嘴产生的涡环相比，孔口产生的环显示出初始涡量损失减少和周围流体的扩散夹带减少。与喷嘴产生的环相比，由孔口产生的涡流环获得更多的循环，更少的环境流体夹带，因此快速传播更长的距离。