By using an axisymmetric immersed-boundary model, we numerically investigate the thrust generation of a deformable body via pulsed jetting. We focus on a single discharging process resulting from the deflation of the body as inspired by the jetting mechanism of cephalopods, such as squids. We examine three jet velocity profiles, namely, impulsive, half-cosine, and cosine, in the relatively low Reynolds number regime. For the impulsive profile, we demonstrate via wake visualization that the leading vortex ring does not pinch off from the trailing jet although its circulation stops growing after a critical formation number (hereby, the formation number is defined as the ratio between the length and diameter of the jet plug) of 6–7. The exact value of the critical formation number depends on the jet velocity profile, suggesting that jet acceleration and viscous dissipation play significant roles in vortex ring evolution. In terms of thrust generation, our results indicate that besides the jet momentum flux, an important source of thrust generation is jet acceleration. The implication is that the jet velocity profile is a key factor in determining the propulsive performance.

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通过轴对称游泳者的形状变形的脉冲喷射推进

通过使用轴对称浸入边界模型，我们数值研究了可变形体通过脉冲喷射产生的推力。我们专注于受到头足类动物（如鱿鱼）喷射机制的启发，由身体放气引起的单一放电过程。我们在相对较低的雷诺数范围内检查了三种射流速度剖面，即脉冲、半余弦和余弦。对于脉冲剖面，我们通过尾流可视化证明，尽管其环流在达到临界地层数后停止增长（因此，地层数被定义为长度和直径之比），但前涡环不会从尾流射流中夹断。喷射塞）6-7。临界地层数的确切值取决于射流速度剖面，表明射流加速度和粘性耗散在涡环演化中起着重要作用。在推力产生方面，我们的结果表明，除了喷流动量通量，推力产生的一个重要来源是喷流加速度。这意味着射流速度剖面是决定推进性能的关键因素。