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首页> 外文期刊>Journal of Fluids and Structures >Free vibrations of an elliptic cylinder at low Reynolds numbers
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Free vibrations of an elliptic cylinder at low Reynolds numbers

机译：低雷诺数时椭圆圆柱的自由振动

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Vortex-induced vibrations of an elliptic cylinder are investigated in the laminar flow regime, 60 <= Re <= 140. The cylinder, in its mean position, is oriented such that either the major axis or the minor axis is aligned parallel to the free-stream flow. The aspect ratio of the cylinder, based on the ratio between the diameter transverse to the free-stream direction and its conjugate, is varied between 0.7 <= AR <= 1.43. A stabilized finite-element method is used to solve the incompressible flow equations and the cylinder motion in two dimensions. The non-dimensional mass of the cylinder is m* = 10.0. The blockage, based on the transverse diameter of the cylinder and lateral width of the domain, is B = 5%. On the basis of vortex shedding patterns and time histories of cylinder oscillation and aerodynamic coefficients, different flow-regimes/branches of the cylinder response are identified. The classically known initial and lower branches are further split into quasi-periodic and periodic parts. Hysteresis, in the response of the cylinder, is studied near the low- (primary hysteresis) and the high- (secondary hysteresis) Re end of lock-in. The width of primary hysteresis, in general, decreases with increase in AR, and disappears completely for AR = 1.43. The width of secondary hysteresis first increases with increase in AR for 0.7 <= AR <= 1.14, and then decreases with further increase in AR. The phase difference between the lift force and transverse displacement shows a jump of approximately 180 degrees at the Re where the ratio of the frequency of the time variation of transverse response to the natural frequency attains a value of unity. The mode of vortex shedding associated with all the flow regimes/branches is either 2S or its variant. In the periodic part of the initial branch, the vortex that is about to be shed from the cylinder coalesces with vortices of the same sign in the near wake. This results in stronger vortices and, therefore, relatively larger fluctuations in the lift force. This mode is named as C-NW(2S). The peak amplitude of cylinder oscillation increases with increase in aspect ratio. An elliptic cylinder whose minor axis is aligned parallel to the free-stream flow experiences larger amplitude of oscillation compared to the case when the major-axis is aligned parallel to the flow. (C) 2014 Elsevier Ltd. All rights reserved.
机译：在层流状态60 <= Re <= 140的条件下研究了椭圆圆柱体的涡激振动。圆柱体在其平均位置的取向使得长轴或短轴平行于自由轴对齐-水流。基于横向于自由流方向的直径与其共轭之间的比率，圆柱体的纵横比在0.7 <= AR <= 1.43之间变化。采用稳定的有限元方法求解二维的不可压缩流动方程和气缸运动。圆柱的无量纲质量为m * = 10.0。基于圆柱的横向直径和域的横向宽度，阻塞为B = 5％。根据涡流的脱落模式和气缸振动的时间历史以及空气动力学系数，确定了气缸响应的不同流态/分支。经典已知的初始分支和下部分支进一步分为准周期性和周期性部分。在锁相的低（初级磁滞）和高（次级磁滞）Re端附近，研究圆柱体的磁滞现象。通常，一次迟滞的宽度随着AR的增加而减小，而对于AR = 1.43则完全消失。对于0.7 <= AR <= 1.14，次级磁滞宽度首先随着AR的增加而增加，然后随着AR的进一步增加而减小。升力和横向位移之间的相位差在Re处显示出大约180度的跃变，其中横向响应的时间变化频率与固有频率之比达到1的值。与所有流态/分支相关的涡旋脱落模式是2S或它的变体。在初始分支的周期性部分中，即将从圆柱体上散发出来的涡流在临近尾流时与具有相同符号的涡流合并。这导致更强的涡流，因此产生较大的升力波动。该模式称为C-NW（2S）。圆柱体振动的峰值幅度随纵横比的增加而增加。与长轴平行于自由流动的情况相比，其短轴平行于自由流流动的椭圆圆柱体具有更大的振荡幅度。 （C）2014 Elsevier Ltd.保留所有权利。

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