On the effective horizontal buoyancy in turbulent thermal convection generated by cell tilting
On the effective horizontal buoyancy in turbulent thermal convection generated by cell tilting
复制标题
DOI：
10.1017/jfm.2020.825
复制
发表时间：
2021-03
影响因子：
3.7
通讯作者：
Lu Zhang;Guang-Yu Ding;K. Xia
中科院分区：
文献类型：
--
作者：
Lu Zhang;Guang-Yu Ding;K. Xia
摘要我们考虑了热对流中全球温度梯度与重力不对准的情况。在这种情况下，产生一个有效的水平浮力，它将显著影响热、质量和动量的输运性质。它还可能改变湍流对流中的流动形态。本文以Rayleigh-Bénard对流为平台，对水平浮力对湍流热对流换热的影响进行了系统的实验和数值研究。在实验上，通过倾斜对流槽，同时增大外加温差，实现了在固定垂直瑞利数(无量纲垂直驱动强度)的情况下增大水平瑞利数(无量纲水平热驱动强度)的条件。我们发现，随着水平与垂直浮力比的增大($varLambda=Ra_H/Ra_V$)，总的热量输送表现为垂直热量输送($Nu_V$)及其水平分量($Nu_H$)的单调增加。然而，在所研究的参数范围内，水平Nusselt数大约比垂直Nusselt数小一个数量级。我们还指出，非零的$Nu_H是由水平浮力引起的系统方位对称性破坏的结果。我们发现，垂直热量输送的增强来自于边界层水平浮力产生的切变的增加。对Prandtl数($Pr$)的影响也进行了数值研究。最后，我们将Grossmann-Lohse理论推广到具有有效水平浮力的情况，其结果成功地预测了$Nu_V(Ra_V，\varLambda，Pr)$。
Abstract We consider the situation of a misalignment between the global temperature gradient and gravity in thermal convection. In such a case an effective horizontal buoyancy arises that will significantly influence the transport properties of heat, mass and momentum. It may also change the flow morphology in turbulent convection. In this paper, we present an experimental and numerical study, using Rayleigh–Bénard convection as a platform, to explore systematically the effect of horizontal buoyancy on heat transport in turbulent thermal convection. Experimentally, a condition of increasing horizontal Rayleigh number ($Ra_H$, which is the non-dimensional horizontal thermal driving strength) under fixed vertical Rayleigh number ($Ra_V$, the non-dimensional vertical driving strength) is achieved by tilting the convection cell and simultaneously increasing the imposed temperature difference. We find that, with increasing horizontal to vertical buoyancy ratio ($\varLambda = Ra_H/Ra_V$), the overall heat transport manifests a monotonic increase in vertical heat transport ($Nu_V$) as well as a monotonic increase in its horizontal component ($Nu_H$). However, the horizontal Nusselt number is found to be approximately one order of magnitude smaller than the vertical Nusselt for the parameter range explored. We also show that the non-zero $Nu_H$ results from the broken azimuthal symmetry of the system induced by the horizontal buoyancy. We find that the enhancement of vertical heat transport comes from the increased shear generated by the horizontal buoyancy at the boundary layer. The effect of Prandtl number ($Pr$) is also studied numerically. Finally, we extend the Grossmann–Lohse theory to the case with an effective horizontal buoyancy, the result of which is successful in predicting $Nu_V(Ra_V,\varLambda ,Pr)$.