Dimensionless parameters for cloudy Rayleigh-Bénard convection: Supersaturation, Damköhler, and Nusselt numbers
Dimensionless parameters for cloudy Rayleigh-Bénard convection: Supersaturation, Damköhler, and Nusselt numbers
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多云瑞利-贝纳德对流的无量纲参数：过饱和度、达姆科勒数和努塞尔数
DOI：
10.1103/physrevfluids.7.010503
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发表时间：
2022
影响因子：
2.7
通讯作者：
Shaw, Raymond A.
中科院分区：
文献类型：
--
作者：
Thomas, Subin;Prabhakaran, Prasanth;Yang, Fan;Cantrell, Will H.;Shaw, Raymond A.
在稳态Rayleigh-Bénard对流中，热量通过湍流热对流从底部热表面传输到顶部冷表面，导致与高度无关的感热通量。当有水汽存在并形成云时，也有额外的潜热通量。多云瑞利-贝纳德对流中的热传输取决于湍流和云的微物理状态：具体来说，是否存在大量的过饱和，以及云的液态水是否通过沉降/沉淀而被去除。在这篇文章中，我们之间的桥梁Rayleigh-Bénard对流文学和大气文学。我们表示的多云对流的无量纲形式的控制方程，从而明确确定的有关多云的情况下，包括施密特，Damköhler，过饱和度和沉降数的控制参数。我们进一步连接到大气文学获得努塞尔数（无量纲热通量）的云对流系统，直接从温度和水蒸气的守恒方程。该通量具有与Zhang等人确定的通量相同的形式。[L. Zhang，K. L. Chong和K.- Q. Xia，J. Fluid Mech.874，1041（2019）10.1017/jfm.2019.463]，但扩展到多云情况。对于相等的热和水蒸气扩散率，通量对应于广泛使用的大气量等效温度和湿静态能量。利用大涡模拟（LES）对一个理想化的有云Rayleigh-Bénard对流系统在固定边界条件下进行模拟，发现等效热通量（Nusselt数）仅弱依赖于系统的微物理细节，如液态水混合比和云滴数浓度。从结果中，我们发现的垂直廓线的感热通量和潜热通量取决于液态水的含量，而等效热通量保持恒定的整个高度的腔室。
In steady-state Rayleigh-Bénard convection, heat is transported by turbulent thermal convection from the bottom, hot surface to the top, cold surface, leading to a height-independent sensible heat flux. When water vapor is present and cloud formation occurs, there is also an additional latent heat flux. Heat transport in cloudy Rayleigh-Bénard convection depends on turbulent flow as well as the microphysical state of the clouds: specifically, whether substantial supersaturations exist and whether cloud liquid water is removed through sedimentation/precipitation. In this article we bridge between the Rayleigh-Bénard convection literature and the atmospheric literature. We express the governing equations for cloudy convection in dimensionless form, thereby explicitly identifying the governing parameters relevant to the cloudy case, including Schmidt, Damköhler, supersaturation, and sedimentation numbers. We further connect to the atmospheric literature by obtaining a Nusselt number (dimensionless heat flux) for a cloud-convection system, directly from the conservation equations for temperature and water vapor. This flux has the same form as that identified by Zhanget al.[L. Zhang, K. L. Chong, and K.-Q. Xia, J. Fluid Mech. 874, 1041 (2019)10.1017/jfm.2019.463] for convection with water vapor, but is extended to the cloudy case. For equal thermal and water vapor diffusivities, the flux corresponds to the widely used atmospheric quantities equivalent temperature and moist static energy. Using large eddy simulation (LES) of an idealized cloudy Rayleigh-Bénard convection system with fixed boundary conditions, we find that the equivalent heat flux (Nusselt number) is only weakly dependent on the microphysical details of the system, such as liquid water mixing ratio and cloud droplet number concentration. From the results, we show the vertical profiles of sensible and latent heat fluxes depend on the liquid water content, whereas the equivalent heat flux remains a constant throughout the height of the chamber.
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