Direct numerical simulations of the swirling von Kármán flow using a semi-implicit moving immersed boundary method
Direct numerical simulations of the swirling von Kármán flow using a semi-implicit moving immersed boundary method
复制标题
使用半隐式移动浸没边界法对旋转冯卡门流进行直接数值模拟
DOI：
10.1016/j.compfluid.2021.105132
复制
发表时间：
2021
影响因子：
2.8
通讯作者：
Bisetti, Fabrizio
中科院分区：
文献类型：
--
作者：
Kasbaoui, M. Houssem;Kulkarni, Tejas;Bisetti, Fabrizio
本文提出了一种新的移动浸没边界方法（IBM），并将其应用于层流和湍流状态下封闭容器内vonKármán旋流的直接数值模拟（DNS）。IBM通过利用时间积分方案扩展了直接强迫方法，该方案将浸没边界强迫步骤嵌入半隐式迭代Crank-Nicolson方案中。整体方法是强大的，稳定的，并产生出色的结果，在典型的情况下，静态和移动的边界。移动的IBM使我们能够再现（F. Ravelet，A. Chiffaudel和F. Daviaud，JFM 601，339（2008））。在这些DNS中，流动由安装有弯曲惯性搅拌器的两个反向旋转叶轮驱动。我们分析了从层流到湍流的过渡，通过增加反向旋转叶轮的转速，以达到四个雷诺数90，360，2000和4000。在层流制度在雷诺数90和360，我们观察到的流动特征类似于那些在实验中报告，特别是，在雷诺数360的外观的破环不稳定性。我们观察到雷诺数2000的过渡湍流。雷诺数为4000时，可实现充分发展的湍流。从模拟计算的无量纲扭矩与实验数据的相关性相匹配。低雷诺数的对称性，随着雷诺数的增加而丢失，恢复在充分发展的湍流制度，在那里我们观察到两个环面对称的中间高度平面的平均流。我们注意到，即使在最高的雷诺数4000，在该装置的中心区域的湍流波动保持各向异性，这表明各向同性需要显着更高的雷诺数。
We present a novel moving immersed boundary method (IBM) and employ it in direct numerical simulations (DNS) of the closed-vessel swirling von Kármán flow in laminar and turbulent regimes. The IBM extends direct-forcing approaches by leveraging a time integration scheme, that embeds the immersed boundary forcing step within a semi-implicit iterative Crank–Nicolson scheme. The overall method is robust, stable, and yields excellent results in canonical cases with static and moving boundaries. The moving IBM allows us to reproduce the geometry and parameters of the swirling von Kármán flow experiments in (F. Ravelet, A. Chiffaudel, and F. Daviaud, JFM 601, 339 (2008)) on a Cartesian grid. In these DNS, the flow is driven by two-counter rotating impellers fitted with curved inertial stirrers. We analyze the transition from laminar to turbulent flow by increasing the rotation rate of the counter-rotating impellers to attain the four Reynolds numbers 90, 360, 2000, and 4000. In the laminar regime at Reynolds number 90 and 360, we observe flow features similar to those reported in the experiments and in particular, the appearance of a symmetry-breaking instability at Reynolds number 360. We observe transitional turbulence at Reynolds number 2000. Fully developed turbulence is achieved at Reynolds number 4000. Non-dimensional torque computed from simulations matches correlations from experimental data. The low Reynolds number symmetries, lost with increasing Reynolds number, are recovered in the mean flow in the fully developed turbulent regime, where we observe two tori symmetrical about the mid-height plane. We note that turbulent fluctuations in the central region of the device remain anisotropic even at the highest Reynolds number 4000, suggesting that isotropization requires significantly higher Reynolds numbers.