Pulsatile jet flows are found in many industrially relevant fluid mechanical problems. A common feature of these flows is that they are fundamentally a series of fluid pulses. This aspect of pulsatile jets implies vortex rings are a basic element of the resulting flow. The significance of this observation is based in part on the tendency of vortex rings to entrain ambient fluid during their formation, but more so on the recent discovery of the phenomenon of vortex ring pinch off. This phenomenon was characterized for starting jets (individual pulses) showing that for pulses sufficiently long with respect to the nozzle diameter (i.e., sufficiently large L/D), the vortex ring stops forming and pinches off from the generating jet. This represents a maximization principle for vortex ring formation and suggests that any effects associated with vortex ring formation in pulsatile jets (e.g., enhanced entrainment), might be able to be optimized by properly selecting the L/D for each pulse.
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机译：在许多工业相关的流体机械问题中发现了脉动射流流动。这些流动的一个共同特征是它们基本上是一系列流体脉冲。脉动喷射的这个方面意味着涡旋环是所得流量的基本元素。该观察结果的重要性部分地基于涡旋环的趋势，以在其形成期间夹带环境流体，但更多的是最近发现涡旋环的现象夹出来的现象。这种现象的特征在于起动喷射喷射（单独脉冲），其示出了对于相对于喷嘴直径（即，足够大的L / D）足够长的脉冲，涡旋环停止形成并从发电射流上夹住。 This represents a maximization principle for vortex ring formation and suggests that any effects associated with vortex ring formation in pulsatile jets (e.g., enhanced entrainment), might be able to be optimized by properly selecting the L/D for each pulse.
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