Coherent structures in tornado-like vortices
Coherent structures in tornado-like vortices
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DOI：
10.1063/1.5111530
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发表时间：
2019-08
影响因子：
4.6
通讯作者：
M. Karami;H. Hangan;L. Carassale;H. Peerhossaini
中科院分区：
文献类型：
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作者：
M. Karami;H. Hangan;L. Carassale;H. Peerhossaini
通过一系列新颖的物理实验和模态分析，对各种涡流比（0.22 ≤ S ≤ 0.96）研究了龙卷风涡流的动力学。观察到各种物理现象，例如漂移、涡流破裂或从一细胞结构到两细胞结构的转变。为了研究龙卷风涡旋的相干结构，应用了两种不同的分解方法：（i）本征正交分解（POD），也称为主成分分析，以及（ii）一种新颖的动态本征正交分解，以提供 POD 模式的时间演化。为了促进对这些 POD 模式的物理解释，我们还在模拟合成涡旋上应用了模态分解。结果表明，在涡流破裂之前的低涡流比下，流动的特征是在较低高度倾斜的单个涡流。对于中间漩涡，在漩涡着陆之前，流动的特征是具有围绕其旋转的单个螺旋的再循环气泡。通过进一步增加涡流比，发生从单螺旋到双螺旋（单室结构到两室结构）的转变。基于这些观察，提出了一种简单的龙卷风涡流结构，可用于为这些类型的流动生成低阶、大规模湍流模型。通过一系列新颖的物理实验和大范围涡流比（0.22 ≤ S ≤ 0.96）的模态分析，研究了龙卷风涡流的动力学。观察到各种物理现象，例如漂移、涡流破裂或从一细胞结构到两细胞结构的转变。为了研究龙卷风涡旋的相干结构，应用了两种不同的分解方法：（i）本征正交分解（POD），也称为主成分分析，以及（ii）一种新颖的动态本征正交分解，以提供 POD 模式的时间演化。为了促进对这些 POD 模式的物理解释，我们还在模拟合成涡旋上应用了模态分解。结果表明，在涡流破裂之前的低涡流比下，流动的特征是在较低高度倾斜的单个涡流。对于中间漩涡，在漩涡着陆之前，流动的特征是具有围绕其旋转的单个螺旋的再循环气泡。 ...
The dynamics of tornadolike vortices is investigated through a set of novel physical experiments and modal analyses for a wide range of swirl ratios (0.22 ≤ S ≤ 0.96). Various physical phenomena such as wandering, vortex breakdown, or transition from one-cell to two-cell structures are observed. To investigate the coherent structure of the tornado vortices, two different decomposition methods are applied: (i) proper orthogonal decomposition (POD), also referred to as principle component analysis, and (ii) a novel dynamic proper orthogonal decomposition to provide time evolutions of the POD modes. To foster the physical interpretation of these POD modes, we also applied modal decomposition on a simulated synthetic vortex. The results show that at low swirl ratios before vortex breakdown, the flow is characterized by a single vortex which is tilted at lower heights. For intermediate swirls, before vortex touchdown, the flow is characterized by a recirculation bubble with a single spiral rotating around it. By further increasing the swirl ratio, transition from a single spiral to a double spiral (one-cell to two-cell structures) occurs. Based on these observations, a simple vortex structure of tornadolike vortex is put forward which can be used to generate a low order, large scale turbulence model for these types of flows.The dynamics of tornadolike vortices is investigated through a set of novel physical experiments and modal analyses for a wide range of swirl ratios (0.22 ≤ S ≤ 0.96). Various physical phenomena such as wandering, vortex breakdown, or transition from one-cell to two-cell structures are observed. To investigate the coherent structure of the tornado vortices, two different decomposition methods are applied: (i) proper orthogonal decomposition (POD), also referred to as principle component analysis, and (ii) a novel dynamic proper orthogonal decomposition to provide time evolutions of the POD modes. To foster the physical interpretation of these POD modes, we also applied modal decomposition on a simulated synthetic vortex. The results show that at low swirl ratios before vortex breakdown, the flow is characterized by a single vortex which is tilted at lower heights. For intermediate swirls, before vortex touchdown, the flow is characterized by a recirculation bubble with a single spiral rotating around it. ...