A pulsed-jet propulsive system which includes a deformable body and a nozzle affixed to it is proposed and numerically examined. The impact of nozzle geometry on the performance of the system during a single discharge at low Reynolds number is studied. A force decomposition algorithm is employed to decouple the thrust into three parts: normal stress at exit, jet flux, and time derivative of internal fluid momentum. This approach enables the investigation of underlying physics in thrust generation. Since its jet flow features negative radial velocity, the system with converging nozzles is found to produce over-pressure (dominant component of the exit normal stress) on the nozzle exit, making positive contributions to thrust. The diverging nozzles, with reversed radial velocity, tend to induce negative pressure on the exit, which diminishes the thrust generation. On the other hand, the contribution from exit pressure only accounts for a relatively small portion of the thrust, which is found to be dominated by the jet flux momentum. As a result, with fixed stroke ratio and time history of deformation the overall thrust generated by the system is determined mostly by the exit size of the nozzle $D^{\prime }$. Specifically, the time-averaged thrust $\overline{F_t}$ is found to be proportional to $1/{D{}^{\prime }}^4$. The geometry of the nozzle also affects the efficiency. For example, the system without a nozzle turns out to be most efficient, followed by one with a short and divergent nozzle.

提出了一种脉冲喷气推进系统，该系统包括一个可变形体和一个固定在其上的喷嘴，并进行了数值研究。研究了在低雷诺数下单次排放期间喷嘴几何形状对系统性能的影响。采用力分解算法将推力解耦为三部分：出口处的法向应力、射流通量和内部流体动量的时间导数。这种方法可以研究推力生成中的基础物理。由于其射流具有负径向速度，因此发现具有收敛喷嘴的系统在喷嘴出口上产生过压（出口法向应力的主要分量），对推力做出积极贡献。具有相反径向速度的发散喷嘴倾向于在出口上产生负压，这减少了推力的产生。另一方面，出口压力的贡献仅占推力的相对较小部分，被发现由射流通量动量主导。因此，在固定冲程比和变形时间历程的情况下，系统产生的总推力主要由喷嘴的出口尺寸决定$D^{\prime }$. 具体来说，时均推力$\overline{F_{吨}}$ 发现与 $1/{D{}^{\prime }}^4$. 喷嘴的几何形状也影响效率。例如，没有喷嘴的系统被证明是最有效的，其次是带有短而发散的喷嘴的系统。