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Parallel simulations of vortex-induced vibrations in turbulent flow: Linear and nonlinear models.

机译：湍流中涡激振动的并行模拟：线性和非线性模型。

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In this work unstructured spectral/hp element based direct numerical simulation (DNS) techniques are used to simulate vortex-induced vibrations (VIV) of flexible cylinders.; Linear structural models are employed for tension-dominated structures (cables) and bending stiffness-dominated structures (beams). Flow-structure interactions are studied in transitional (200–300) and turbulent (1000) Reynolds numbers. Structural responses as well as hydrodynamic forces are analyzed and their relationship with the near wake flow structures is examined. The following conclusions were reached: (1) A Reynolds number effect exists for the observed oscillation amplitude. (2) The phase relationship between cross-flow displacement and coefficient of lift is correlated with both the magnitudes of lift forces and displacement. (3) Cables enhance transition to turbulent flow, while beams (and rigidly vibrating cylinders) delay it. In the transition regime beams oscillate with 70% of the amplitude of cables. (4) Oblique and parallel shedding appear to coexist in the turbulent wake of cables and beams with a traveling wave structural response. The corresponding wake structure behind a cylinder with pinned ends vibrating as a standing wave, displays lambda-type vortices similar to those seen at lower (laminar) Reynolds numbers. (5) Cables and beams at a Reynolds number of 1000 give: (a) extremely similar velocity spectra, (b) differing autocorrelation profiles and large flow structures, and (c) differing structural responses. (6) The empirical formula for the coefficient of drag due to Skop et al. (1977) is shown to be in disagreement with the experimental data; a modified formula fits the results much better.; A non-linear set of equations for the finite amplitude vibrations of a string are also derived and investigated. It is combined with an Arbitrary Lagrangian-Eulerian (ALE) flow solver and applied to model simulations of low Reynolds number (100) flow past flexible cylinders with pinned ends. It is noted that: (1) The string tension shows considerable variability with time and to a lesser extent along the span, giving rise to non-classical lock-in phenomena. (2) The coupled flow-structure system is very sensitive to large tension variations in the initial conditions. (3) The hydrodynamic forces in the spanwise direction are non-negligible.
机译：在这项工作中，基于非结构化频谱/ hp元素的直接数值模拟（DNS）技术用于模拟柔性圆柱体的涡激振动（VIV）。线性结构模型用于以张力为主的结构（电缆）和以弯曲刚度为主的结构（梁）。研究了流固耦合的过渡（200–300）和湍流（1000）雷诺数。分析了结构响应以及流体动力，并检查了它们与近尾流结构的关系。得出以下结论：（1）对于观察到的振荡幅度存在雷诺数效应。 （2）错流位移与升力系数之间的相位关系与升力和位移的大小有关。 （3）电缆增强了湍流的过渡，而梁（和刚性振动的圆柱体）则延迟了湍流。在过渡状态下，光束以电缆振幅的70％振荡。 （4）倾斜和平行脱落似乎并存于具有行波结构响应的电缆和梁的湍流尾流中。圆柱体后部的相应尾流结构（带有固定端）会像驻波一样振动，显示出的λ型涡流类似于在较低（层状）雷诺数下看到的涡流。 （5）雷诺数为1000的电缆和横梁给出：（a）极相似的速度谱，（b）不同的自相关轮廓和大的流动结构，以及（c）不同的结构响应。 （6）Skop等人的阻力系数经验公式。 （1977）被证明与实验数据不一致；修改后的公式更适合结果。还导出并研究了弦的有限振幅振动的非线性方程组。它与任意Lagrangian-Eulerian（ALE）流量求解器结合使用，并应用于低雷诺数（100）流经带固定端的柔性圆柱体的模型仿真。需要注意的是：（1）弦线张力随时间变化很大，并且在跨度上变化较小，从而引起非经典的锁定现象。 （2）耦合流动结构系统对初始条件下的大张力变化非常敏感。 （3）翼展方向的水动力不可忽略。

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