论文标题

湍流涡流中不对称的时空演化

Spatiotemporal evolution of asymmetries in turbulent trailing vortices

论文作者

Khodkar, M. A.

论文摘要

研究了最初引入轴对称湍流的不对称的外部传播,其中3D批量涡流在高雷诺数处的3D批量涡流和任意旋转数字作为测试用例选择。众所周知,在径向向外传播的2D轴对称流中的干扰(不对称)是为了重新对称涡流,但不再以临界距离行进,称为停滞半径。我们利用直接的数值模拟(DNS)和一个无关模型,它是通过在螺旋坐标中线性的激励和涡度传输方程线来形成的,以证明与2D情况相反,3D涡流可以启用Asymmmetries的无结合的辐射。我们进一步将Wenzel-Kramers-brillouin(WKB)分析应用于线性模型,将扰动视为紧凑型波袋,以将线性模型的PDE转换为几种ODES。然而,在气候科学界已经表明,WKB方法无处不在地预测了引入3D旋风式涡流引入的干扰的停滞半径和高度,在这里,我们确定了狭窄的参数范围,WKB分析还支持无抑制的动态传播。最后,使用线性快速失真理论和数值模拟阐明了在不同阶段和位置控制动量传输的机制,从而促进了扰动的外向对流。由于完整的Navier-Stokes方程的DNS迅速稳定在层状构型上,因此还进行了线性化的传输方程和无线性管理方程,而无需基础流相互作用,以揭示出主要的生长和辐射式生长的生长次数的生长,以揭示主要的机制。

The outward propagation of asymmetries introduced to originally axisymmetric turbulent flows is investigated, where 3D Batchelor vortices at high Reynolds numbers and with arbitrary swirl numbers are chosen as test cases. It is well known that disturbances (asymmetries) added to a 2D axisymmetric flow propagate radially outward, in order to re-axisymmetrize the vortex, but cease to travel at a critical distance, known as the stagnation radius. We utilize direct numerical simulations (DNS) and an inviscid model developed by linearizing the momentum and vorticity transport equations around the base (unperturbed) flow in helical coordinates to demonstrate that, in contrast with 2D cases, 3D vortices enable the unbounded radial propagation of asymmetries. We further apply the Wenzel-Kramers-Brillouin (WKB) analysis to the linear model, treating perturbations as compact wavepackets, to transform the PDEs of the linear model to a few ODEs. However it has been shown in the climate science community that the WKB approach ubiquitously predicts stagnation radii and heights for disturbances introduced to 3D cyclone-like vortices, here, we identify a narrow range of parameters, for which the WKB analysis also supports an unrestrained propagation for disturbances. Finally, the mechanisms governing the momentum transport at different stages and locations, thereby promoting the outward advection of perturbations, are elucidated using the the linear rapid distortion theory and numerical simulations. Since the DNS of the full Navier-Stokes equations rapidly stabilizes to a laminar configuration, the DNS of the linearized transport equations and the nonlinear governing equations without base-flow interactions are also conducted, in order to uncover the primary mechanisms for the growth and radial propagation of perturbations as well as the nonlinear processes causing growth arrest at fixed swirl numbers.

扫码加入交流群

加入微信交流群

微信交流群二维码

扫码加入学术交流群,获取更多资源