A pulsed jet with a period of no flow between pulses (i.e., a fully pulsed jet) produces a multiplicity of vortex rings whose characteristics are determined by the jet pulsing parameters. The present study analyzes the case of impulsively initiated and terminated jet pulses in the limit of equal pulse duration and period to determine the minimum possible vortex ring separation obtainable from a fully pulsed jet. The downstream character of the flow is modeled as an infinite train of thin, coaxial vortex rings. Assuming inviscid flow and matching the circulation, impulse, kinetic energy, and frequency of the jet and vortex ring train allow the properties of the vortex ring train to be determined in terms of the ratio of jet slug length-to-diameter ratio (L/D) used for each pulse. The results show the minimum ring separation may be made arbitrarily small as L/D is decreased and the corresponding total ring velocity remains close to half the jet velocity for L/D 1.5. The results are discussed in the context of models of pulsed-jet propulsion.
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机译：在脉冲之间没有流动周期的脉冲状射流（即，完全脉冲射流）产生多个涡流环，其特性由射流脉冲参数确定。本研究分析了在相等的脉冲持续时间和周期的极限内脉冲启动和终止的喷射脉冲的情况，以确定从全脉冲喷射可获得的最小可能的涡流环分离。流动的下游特征被建模为无限细的同轴涡流环。假设无粘性流量并匹配射流和涡流环列的循环，冲量，动能以及频率，则可以根据射流塞长度与直径之比（L / D）用于每个脉冲。结果表明，随着L / D的减小，最小的环间距可以任意减小，并且相应的总环速度保持接近L / D 1.5的射流速度的一半。在脉冲喷射推进模型的背景下讨论了结果。
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