论文标题
定期调制热对流
Periodically modulated thermal convection
论文作者
论文摘要
许多天然和工业湍流都遭受时间依赖时间的边界条件。尽管无处不在，但几乎没有研究时间调制（带有频率$ f $）对全球运输属性的影响。在这里，我们在温度边界条件下使用时间周期性调制对Rayleigh-Bénard（RB）对流进行数值模拟，并报告该调制如何导致明显的热通量（Nusselt Numeselt $ \ rm \ rm {nu} $）增强。使用Stokes热边界层的概念，我们可以解释NU增强的开始频率以及NU最大值的最佳频率，以及它们如何依赖Rayleigh Number ra和Prandtl数字$ \ rm {pr} $。由此，我们在3D参数空间（$ f $，$ \ rm {ra} $，$ \ rm {pr} $）中构造一个相图，并识别：（i）调制太快而无法影响$ \ rm {nu} $; （ii）中等调制制度，其中$ \ rm {nu} $随着$ f $的减少和（iii）缓慢的调制制度而增加，其中$ \ rm {nu} $随着$ f $的进一步减少而减少。我们的发现提供了一个框架，可以通过时间依赖性强迫研究其他类型的湍流。
Many natural and industrial turbulent flows are subjected to time-dependent boundary conditions. Despite being ubiquitous, the influence of temporal modulations (with frequency $f$) on global transport properties has hardly been studied. Here, we perform numerical simulations of Rayleigh-Bénard (RB) convection with time periodic modulation in the temperature boundary condition and report how this modulation can lead to a significant heat flux (Nusselt number $\rm{Nu}$) enhancement. Using the concept of Stokes thermal boundary layer, we can explain the onset frequency of the Nu enhancement and the optimal frequency at which Nu is maximal, and how they depend on the Rayleigh number Ra and Prandtl number $\rm{Pr}$. From this, we construct a phase diagram in the 3D parameter space ($f$, $\rm{Ra}$, $\rm{Pr}$) and identify: (i) a regime where the modulation is too fast to affect $\rm{Nu}$; (ii) a moderate modulation regime, where $\rm{Nu}$ increases with decreasing $f$ and (iii) slow modulation regime, where $\rm{Nu}$ decreases with further decreasing $f$. Our findings provide a framework to study other types of turbulent flows with time-dependent forcing.
