Department of Mechanical Engineering, Southern Methodist University, Dallas, TX 75275, USA.
Bioinspir Biomim. 2010 Sep;5(3):036003. doi: 10.1088/1748-3182/5/3/036003. Epub 2010 Aug 16.
The effect of the velocity program and duty cycle (St(L)) on the propulsive efficiency of pulsed-jet propulsion was studied experimentally on a self-propelled, pulsed-jet underwater vehicle, dubbed Robosquid due to the similarity of essential elements of its propulsion system with squid jet propulsion. Robosquid was tested for jet slug length-to-diameter ratios (L/D) in the range 2-6 and St(L) in the range 0.2-0.6 with jet velocity programs commanded to be triangular or trapezoidal. Digital particle image velocimetry was used for measuring the impulse and energy of jet pulses to calculate the pulsed-jet propulsive efficiency and compare it with an equivalent steady jet system. Robosquid's Reynolds number (Re) based on average vehicle velocity and vehicle diameter ranged between 1300 and 2700 for the conditions tested. The results indicated better propulsive efficiency of the trapezoidal velocity program (up to 20% higher) compared to the triangular velocity program. Also, an increase in the ratio of the pulsed-jet propulsive efficiency to the equivalent steady jet propulsive efficiency (eta(P)/eta(P, ss)) was observed as St(L) increased and L/D decreased. For cases of short L/D and high St(L), eta(P)/eta(P, ss) was found to be as high as 1.2, indicating better performance of pulsed jets. This result demonstrates a case where propulsion using essential elements of a biological locomotion system can outperform the traditional mechanical system equivalent in terms of efficiency. It was also found that changes in St(L) had a proportionately larger effect on propulsive efficiency compared to changes in L/D. A simple model is presented to explain the results in terms of the contribution of over-pressure at the nozzle exit plane associated with the formation of vortex rings with each jet pulse.
对自推进脉冲射流水下航行器 Robosquid 进行了实验研究，以探讨速度程序和占空比（St（L））对脉冲射流推进器的推进效率的影响，由于其推进系统的基本要素与鱿鱼射流推进非常相似，因此将 Robosquid 称为 Robosquid。 Robosquid 的射流弹体长径比（L/D）范围为 2-6，St（L）范围为 0.2-0.6，射流速度程序命令为三角形或梯形。数字粒子图像测速法用于测量射流脉冲的冲量和能量，以计算脉冲射流推进效率，并将其与等效稳态射流系统进行比较。 Robosquid 的基于平均车辆速度和车辆直径的雷诺数（Re）在测试条件下介于 1300 和 2700 之间。结果表明，与三角形速度程序相比，梯形速度程序的推进效率更高（高达 20%）。此外，随着 St（L）的增加和 L/D 的减小，观察到脉冲射流推进效率与等效稳态射流推进效率的比值（eta（P）/eta（P，ss））增加。对于 L/D 短和 St（L）高的情况，发现 eta（P）/eta（P，ss）高达 1.2，表明脉冲射流的性能更好。这一结果表明，在效率方面，使用生物运动系统的基本要素进行推进可以胜过传统的机械系统等效物。还发现，与 L/D 的变化相比，St（L）的变化对推进效率的影响更大。提出了一个简单的模型，以根据与每个射流脉冲形成的涡环相关的喷嘴出口平面上的过压的贡献来解释结果。
