An explicit algebraic closure for passive scalar-flux: Applications in heated channel flows subjected to system rotation

通过对流流动和薄膜冷凝实现排斥盐分的连续被动式太阳能热脱盐

Salt-rejecting continuous passive solar thermal desalination via convective flow and thin-film condensation

针对被动式太阳能脱盐中毛细吸水结构无法连续排盐及冷凝器效率低的问题，设计了被动式倒置单级太阳能膜脱盐器，利用重力驱动盐水流动连续排盐并结合微孔膜薄膜冷凝降低蒸汽传输阻力，实现7天连续运行和32.2%的太阳能-水效率。

Diffusion of a passive scalar by convective flows under parametric disorder

We study transport of a weakly diffusive pollutant (a passive scalar) by thermoconvective flow in a fluid-saturated horizontal porous layer heated from below under frozen parametric disorder. In the presence of disorder (random frozen inhomogeneities of the heating or of macroscopic properties of the porous matrix), spatially localized flow patterns appear below the convective instability threshold of the system without disorder. Thermoconvective flows crucially effect the transport of a pollutant along the layer, especially when its molecular diffusion is weak. The effective (or eddy) diffusi…

Almost-sure exponential mixing of passive scalars by the stochastic Navier-Stokes equations

We deduce almost-sure exponentially fast mixing of passive scalars advected by solutions of the stochastically-forced 2D Navier-Stokes equations and 3D hyper-viscous Navier-Stokes equations in $\mathbb T^d$ subjected to non-denegenerate $H^σ$-regular noise for any $σ$ sufficiently large. That is, for all $s > 0$ there is a deterministic exponential decay rate such that all mean-zero $H^s$ passive scalars decay in $H^{-s}$ at this same rate with probability one. This is equivalent to what is known as \emph{quenched correlation decay} for the Lagrangian flow in the dynamical systems literature. …

The Batchelor spectrum of passive scalar turbulence in stochastic fluid mechanics at fixed Reynolds number

In 1959, Batchelor predicted that the stationary statistics of passive scalars advected in fluids with small diffusivity $κ$ should display a $|k|^{-1}$ power spectrum along an inertial range contained in the viscous-convective range of the fluid model. This prediction has been extensively tested, both experimentally and numerically, and is a core prediction of passive scalar turbulence. In this article we provide a rigorous proof of a version of Batchelor's prediction in the $κ\to 0$ limit when the scalar is subjected to a spatially-smooth, white-in-time stochastic source and is advected by t…

Convection in rotating flows with simultaneous imposition of radial and vertical temperature gradients

Laboratory experiments were conducted to study heat transport characteristics in a nonhomogeneously heated fluid annulus subjected to rotation along the vertical axis (z). The nonhomogeneous heating was obtained by imposing radial and vertical temperature gradient (ΔT). The parameter range for this study was Rayleigh number, Ra=2.43x10^8-3.66x10^8, and Taylor number, Ta=6.45x10^8-27x10^8. The working fluid was water with a Prandtl number, Pr=7. Heat transport was measured for varying rotation rates (Ω) for fixed values of ΔT. The Nusselt number, Nu, plotted as a function of Ta distinctly showe…

湍流中标量输运的最小耗散模型与保对称离散化

Minimum-dissipation model and symmetry-preserving discretization for scalar transport in a turbulent flow

本研究将最小耗散模型扩展至标量输运，结合保对称离散化，在OpenFOAM差分加热腔中验证，显著提升高度拉伸网格上流动与传热预测。

Direct Numerical Simulation of High Prandtl Number Fluid Flow in the Downcomer of an Advanced Reactor

The passive safety is a crucial feature of advanced nuclear reactor (Gen IV) design. During loss of power scenarios, the downcomer plays a crucial role. The fluid-flow behavior in the downcomer can involve forced to mixed to natural convection and characterizing the heat transfer for these changing regimes is a daunting challenge. High-resolution heat transfer numerical database can potentially support the development of precise and affordable reduced resolution heat transfer models. These models can be designed based on a multiscale hierarchy developed as part of the recently DOE-funded cente…

Flow-Induced Deformation of a Flexible Thin Structure as Manifestation of Heat Transfer Enhancement

Flow-induced deformation of thin structures coupled with convective heat transfer has potential applications in energy harvesting and is important for understanding functioning of several biological systems. We numerically demonstrate large-scale flow-induced deformation as an effective passive heat transfer enhancement technique. An in-house, strongly-coupled fluid-structure interaction (FSI) solver is employed in which flow and structure solvers are based on sharp-interface immersed boundary and finite element method, respectively. In the present work, we validate convective heat transfer mo…

Lagrangian chaos and scalar advection in stochastic fluid mechanics

We study the Lagrangian flow associated to velocity fields arising from various models of fluid mechanics subject to white-in-time, $H^s$-in-space stochastic forcing in a periodic box. We prove that in many circumstances, these flows are chaotic, that is, the top Lyapunov exponent is strictly positive. Our main results are for the Navier-Stokes equations on $\mathbb T^2$ and the hyper-viscous regularized Navier-Stokes equations on $\mathbb T^3$ (at arbitrary Reynolds number and hyper-viscosity parameters), subject to forcing which is non-degenerate at high frequencies. As an application, we st…

双叶瓣闭合与反流防止：叶let几何学的作用

Bicuspid Valve Closure and Backflow Prevention: Role of Leaflet Geometry

研究双叶瓣的叶let几何形状如何影响反流防止效率，通过数值模拟分析叶let长度对反流控制的影响，揭示叶let形状和刚性对阀门功能的关键作用。

湍流可渗透通道流的终极状态

The ultimate state of turbulent permeable-channel flow

本研究通过直接数值模拟发现，可渗透通道流在雷诺数超过10^4时进入终极状态，摩擦系数和斯坦顿数均趋于常数，其机制是开尔文-亥姆霍兹不稳定性产生的大尺度展向涡旋，实现了不依赖热扩散率的终极传热。