论文标题
电水力动力流中的莫法特涡流:数值模拟和分析
Moffatt eddies in electrohydrodynamic flows: numerical simulations and analyses
论文作者
论文摘要
我们从数值上研究了介电液体的二维电水动力学(EHD)流中的一系列涡流,这是由双曲线叶片电极和平板电极(或叶片板构型)之间的电势差驱动的。电动流动在板上撞击以产生涡旋,类似于莫法特(Moffatt)涡流(Moffatt,$ \ textit {J。FluidMech。} $ 18,1-18,1964)。 EHD中的这种现象首先在Perri $ \ textit {等,J。FluidMech。} $ vol的实验工作中报道。 900,A12,2020。我们在一个大型计算域中使用三个Moffatt-type涡流进行EHD流量的直接数值模拟,该型号是中等电动雷利数字($ t $,量化了电场的强度)。检查了相邻涡流的大小和强度之比,并可以与莫法特的理论预测进行比较。有趣的是,对于远场的两个涡流而言,定量比较非常准确。我们的调查还表明,较大的$ t $增强了涡旋强度,并且更强的电荷扩散效果会扩大涡旋尺寸。足够大的$ t $可以进一步导致与实验观察一致的振荡流。此外,还进行了稳定叶片板EHD流动的全球稳定性分析。全局模式的细节为$ t $的不同值。当$ t $很大时,中心区域中几何的限制效应可能会导致振荡频率增加。这项工作有助于莫法特型涡流的定量表征。
We study numerically a sequence of eddies in two-dimensional electrohydrodynamic (EHD) flows of a dielectric liquid, driven by an electric potential difference between a hyperbolic blade electrode and a flat plate electrode (or the blade-plate configuration). The electrically-driven flow impinges on the plate to generate vortices, which resemble Moffatt eddies (Moffatt, $\textit{J. Fluid Mech.}$ vol. 18, 1-18, 1964). Such a phenomenon in EHD was first reported in the experimental work of Perri $\textit{et al., J. Fluid Mech.}$ vol. 900, A12, 2020. We conduct direct numerical simulations of the EHD flow with three Moffatt-type eddies in a large computational domain at moderate electric Rayleigh numbers ($ T $, quantifying the strength of the electric field). The ratios of size and intensity of the adjacent eddies are examined and they can be compared favourably to the theoretical prediction of Moffatt; interestingly, the quantitative comparison is remarkably accurate for the two eddies in the farfield. Our investigation also shows that a larger $T$ strengthens the vortex intensity, and a stronger charge diffusion effect enlarges the vortex size. A sufficiently large $T$ can further result in an oscillating flow, consistent with the experimental observation. In addition, a global stability analysis of the steady blade-plate EHD flow is conducted. The global mode is detailedly characterised at different values of $T$. When $T$ is large, the confinement effect of the geometry in the center region may lead to an increased oscillation frequency. This work contributes to the quantitative characterisation of the Moffatt-type eddies in electrohydrodynamic flows.