On the effects of vertical offset and core structure in streamwise-oriented vortex–wing interactions
On the effects of vertical offset and core structure in streamwise-oriented vortex–wing interactions
复制标题
流向涡翼相互作用中垂直偏移和核心结构的影响
DOI：
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发表时间：
2016
影响因子：
3.7
通讯作者：
P. Huang
中科院分区：
文献类型：
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作者：
C. Barnes;M. Visbal;P. Huang
本文研究了有限展弦比机翼上流向涡的三维流动结构。入射涡相对于机翼的垂直位置对非定常流结构有显著影响。流向涡的直接冲击在前缘上游的涡中产生螺旋不稳定性，使人联想到Batchelor涡的螺旋不稳定模式。一个小的负的垂直偏移发展一个更明显的不稳定性，而一个正的垂直偏移完全消除了不稳定性。垂直位置的这些差异是机翼提供的压力梯度的上游影响的结果。直接冲击或负垂直偏移使涡流受到逆压力梯度的影响，导致轴向速度降低和涡流减少，从而导致流体动力学不稳定性。相反，正的垂直偏移通过使流向涡与有利的压力梯度成直线来消除不稳定性，从而增强涡流并抑制不稳定模式的增长。在每种情况下，螺旋不稳定性只发生在入射涡的属性落在线性稳定性理论预测的不稳定性阈值。与下游分离和失速相关的压力梯度的影响也有可能在正垂直偏移时引入吸力面不稳定性。对于较大的涡流，机翼的影响更为严重，由于干扰较弱和粘性稳定性增加，机翼的影响随着涡流的大小而减小。螺旋不稳定不是直接撞击的唯一可能结果。射流状涡流和尾流状涡流中的较高涡流比可以在撞击时保持稳定性，导致层流涡流在机翼两侧分裂。
This article explores the three-dimensional flow structure of a streamwise-oriented vortex incident on a finite aspect-ratio wing. The vertical positioning of the incident vortex relative to the wing is shown to have a significant impact on the unsteady flow structure. A direct impingement of the streamwise vortex produces a spiralling instability in the vortex just upstream of the leading edge, reminiscent of the helical instability modes of a Batchelor vortex. A small negative vertical offset develops a more pronounced instability while a positive vertical offset removes the instability altogether. These differences in vertical position are a consequence of the upstream influence of pressure gradients provided by the wing. Direct impingement or a negative vertical offset subject the vortex to an adverse pressure gradient that leads to a reduced axial velocity and diminished swirl conducive to hydrodynamic instability. Conversely, a positive vertical offset removes instability by placing the streamwise vortex in line with a favourable pressure gradient, thereby enhancing swirl and inhibiting the growth of unstable modes. In every case, the helical instability only occurs when the properties of the incident vortex fall within the instability threshold predicted by linear stability theory. The influence of pressure gradients associated with separation and stall downstream also have the potential to introduce suction-side instabilities for a positive vertical offset. The influence of the wing is more severe for larger vortices and diminishes with vortex size due to weaker interaction and increased viscous stability. Helical instability is not the only possible outcome in a direct impingement. Jet-like vortices and a higher swirl ratio in wake-like vortices can retain stability upon impact, resulting in the laminar vortex splitting over either side of the wing.