标题： 绕线鳍弹丸异常滚转力矩的机理研究 显示英文标题

标题： Mechanism for the Anomalous Roll Moment in Wraparound Fin Projectiles

摘要： 带缠绕弹翼（WAF）的弹药即使在零攻角的情况下也会出现非对称滚转力矩，并且它们可能导致翻滚反转和共振不稳定性，这一点早已被认识。 观察到诱导滚转力矩的符号会根据WAF配置（凹面朝前或反之）以及亚音速和超音速马赫数之间而改变。 在这项工作中，我们提出了一种简单的机制，可以解释WAF弹药在亚音速范围内的异常滚转行为。 通过将弯曲弹翼建模为离散的展向线性段，缠绕弹翼可以近似为带有偏转小翼的机翼，并且文献中对于此类机翼构型的实验数据可以应用于WAF弹药的弯曲弹翼。 弯曲弹翼的升力特性可以根据机翼尖端相对于局部流动迎角是向上还是向下偏转而有所不同。 基于WAF火箭上一对相反放置的弯曲弹翼之间的这种升力差异，可以解释诱导滚转力矩的符号及其对小攻角下自由流攻角的依赖性。 这种升力差异的物理机制，因此诱导滚转力矩，可以追溯到缠绕弹翼尖端涡流的展向位置和起飞高度。 显示英文摘要

摘要： The occurrence of asymmetric rolling moments in wraparound fin (WAF) projectiles, even at zero free stream angle of attack, and their potential to induce roll reversal and resonant instabilities has long been recognized. The induced rolling moment is seen to flip sign depending on the WAF configuration (with concave surface leading into the roll or vice versa), and between subsonic and supersonic Mach numbers. In this work, we propose a simple mechanism that can explain the anomalous rolling behavior of WAF projectiles in the subsonic regime. By modeling the curved fin by discrete span-wise linear segments, the wraparound fin can be approximated as a wing with a deflected winglet, and the experimental data available in the literature for such wing configurations can be applied to the curved fin of WAF projectiles. The lifting characteristic of the curved fin can be seen to differ depending on whether the wingtip appears to be deflected up or down relative to the local flow incidence angle. Based on this differential lift between a pair of oppositely-placed curved fins on a WAF rocket, it becomes possible to explain the observed sign of the induced rolling moment as well as its dependence on the free stream angle of attack for small values of the angle of attack. The physical mechanism for the differential lift, and hence the induced rolling moment, can be traced to the span-wise location and the liftoff height of the tip vortex from the wraparound fin tips.