Effect of trailing-edge shape on the self-propulsive performance of heaving flexible plates
Effect of trailing-edge shape on the self-propulsive performance of heaving flexible plates
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DOI：
10.1017/jfm.2019.1076
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发表时间：
2020-01
影响因子：
3.7
通讯作者：
Chengyao Zhang;Haibo Huang;Xi-yun Lu
中科院分区：
文献类型：
--
作者：
Chengyao Zhang;Haibo Huang;Xi-yun Lu
数值研究了后缘形状对三维柔性板自推性能的影响。在我们的研究中，板的后缘是对称的人字形，后缘角从$30^{CIRC}$(凹板)到$150^{\CIRC}$(凸板)不等。在不同的弯曲刚度$K$下，确定了推进速度$U和效率$\Unicode[STIX]{x1D702}$作为$\Unicode[STIX]{x1D719}$的函数的三个推进性能区域。当$K$较小、中等和较大时，方板、凸板和凹板的性能分别达到最佳。对旋涡结构和速度场的分析表明，通常情况下，性能最好的平板后面的射流最长。此外，射流的倾角可能较小。推进器在小K值和中等K值时的不同推进性能主要归因于后缘相位滞后。分析了作用在平板上的力，推力主要由法向力贡献。如果用板的法向力和面积力矩重新缩放$U$、$\Unicode[STIX]{x1D702}$和$K$，则当弯曲刚度系数较小或中等时，不同$\Unicode[STIX]{x1D719}$的曲线几乎崩溃为一条曲线。标度证实，在小或中等$K$时，法向力应该是特征流体力，而$\Unicode[stix]{x1D719}$效果受面积矩控制。这一发现可能会对水生动物的推进性能有所帮助。
The effect of trailing-edge shape on the self-propulsive performance of three-dimensional flexible plates is studied numerically. In our study, the trailing edges of the plates are symmetric chevron shapes, and the trailing-edge angle $\unicode[STIX]{x1D719}$ varies from $30^{\circ }$ (concave plate) to $150^{\circ }$ (convex plate). Under different bending stiffnesses $K$, three regimes of the propulsive performance in terms of propulsive velocity $U$ and efficiency $\unicode[STIX]{x1D702}$ as a function of $\unicode[STIX]{x1D719}$ are identified. When $K$ is small, moderate and large, the square, convex and concave plate achieves the best performance, respectively. Analyses of vortical structures and velocity fields show that usually the jet behind the plate with the best performance is longest. Besides, the inclination angle of the jet may be small. The different propulsive performances at small and moderate $K$ are mainly attributed to the phase lag of the trailing edge. The force acting on the plate is analysed and it is found that the thrust force is mainly contributed by the normal force. If $U$, $\unicode[STIX]{x1D702}$ and $K$ are rescaled by the normal force and the area moment of the plate, the curves for different $\unicode[STIX]{x1D719}$ almost collapse into a single curve when the bending stiffness coefficient is small or moderate. The scaling confirms that the normal force should be the characteristic fluid force at small or moderate $K$ and the $\unicode[STIX]{x1D719}$ effect is governed by the area moment. The findings may shed some light on the propulsive performance of aquatic animals.