arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2006.04301physics.flu-dyn
收藏

Rayleigh-Taylor turbulence中的尺度相互作用和各向异性

Scale interactions and anisotropy in Rayleigh-Taylor turbulence

Dongxiao Zhao, Riccardo Betti, Hussein Aluie

摘要:

我们研究了瑞利-泰勒(RT)流的能量尺度传递,通过粗粒化的物理空间没有傅立叶变换,允许沿垂直方向的尺度分析。两个过程负责跨尺度的动能通量:大尺度压力梯度作用于小尺度密度和速度的气压密度功$Λ$,以及多尺度速度的形变功$Π$。我们的粗粒化分析表明,这些通量表现出自相似的演变,是二次的时间,类似RT混合层。我们发现,$Λ$是一个管道的势能,转移能量的非本地从最大规模的惯性范围内的较小规模的$Π$接管。在3D中,$Π$继续持续级联到较小的尺度,而在2D中,$Π$将能量重新引导回较大的尺度,尽管在2D变密度流中缺乏涡度守恒。这导致了2D-RT中的正反馈回路(3D中不存在),其中混合层生长和相关的势能释放相对于3D增强,解释了2D模拟中经常观察到的较大的$α$值。尽管在2D中有更高的体动能水平,但小惯性尺度比3D中弱。此外,与3D形成鲜明对比的是,2D中的净高档叶栅倾向于使大尺度流动各向同性。我们的研究结果表明,在3D-RT的净高档能量转移的情况下,通常声称,大规模的泡沫和尖峰的增长是不是由于“合并”,而仅仅是由于气压密度工作$Λ$。

英文摘要:

We study energy scale-transfer in Rayleigh-Taylor (RT) flows by coarse-graining in physical space without Fourier transforms, allowing scale analysis along vertical direction. Two processes are responsible for kinetic energy flux across scales: baropycnal work $Λ$, due to large-scale pressure gradients acting on small-scales of density and velocity, and deformation work $Π$, due to multi-scale velocity. Our coarse-graining analysis shows how these fluxes exhibit self-similar evolution that is quadratic-in-time, similar to RT mixing layer. We find that $Λ$ is a conduit for potential energy, transferring energy non-locally from the largest scales to smaller scales in the inertial range where $Π$ takes over. In 3D, $Π$ continues a persistent cascade to smaller scales, whereas in 2D $Π$ re-channels the energy back to larger scales despite the lack of vorticity conservation in 2D variable density flows. This gives rise to a positive feedback loop in 2D-RT (absent in 3D) in which mixing layer growth and the associated potential energy release are enhanced relative to 3D, explaining the oft-observed larger $α$ values in 2D simulations. Despite higher bulk kinetic energy levels in 2D, small inertial scales are weaker than in 3D. Moreover, the net upscale cascade in 2D tends to isotropize the large-scale flow, in stark contrast to 3D. Our findings indicate the absence of net upscale energy transfer in 3D-RT as is often claimed; growth of large-scale bubbles and spikes is not due to "mergers" but solely due to baropycnal work $Λ$.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑