E. V. Votyakov, E. Zienicke
The paper presents 3D numerical results for the laminar liquid metal flow in a rectangular duct compared with experimental results. It is shown that the magnetic interaction parameter $N$ is the main parameter governing the flow provided turbulent pulsations are locally suppressed by magnetic field.
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Flow of a shear-thinning fluid in a rectangular duct
本研究针对矩形管道内剪切稀化流体稳态层流无精确解的问题，得到Carreau流体情形的精确解并数值分析，揭示流变性与宽高比的独立影响，推导得到通用标度与公式。
We carry out Direct Numerical Simulation (DNS) of flows in closed rectangular ducts with several aspect ratios. The Navier-Stokes equations are discretized through a second-order finite difference scheme, with non-uniform grids in two directions. The duct cross-sectional area is maintained constant as well as the flow rate, which allows to investigate which is the appropriate length scale in the Reynolds number for a good scaling in the laminar and in the fully turbulent regimes. We find that the Reynolds number based on the half length of the short side leads to a critical Reynolds number whi…
The linear stability of stratified two-phase flows in rectangular ducts is studied numerically. The linear stability analysis takes into account all possible infinitesimal three-dimensional disturbances and is carried out by solution of the associated eigenproblem. The neutral stability boundary and the corresponding critical wave number are obtained for liquid - liquid and air - water systems. Depending on the problem parameters, the instability sets in owing to short, intermediate, of long wave most unstable perturbations. Patterns of the most unstable disturbances are reported and discussed…
This paper reports high resolution simulations using a fifth-order weighted essentially non-oscillatory (WENO) scheme with a third order TVD Runge-Kutta time stepping method to examine the features of detonation front and physics in square ducts. The simulations suggest that two and three-dimensional detonation wave front formations are greatly enhanced by the presence of transverse waves. The motion of transverse waves generates triple points (zones of high pressure and large velocity coupled together), which cause the detonation front to become locally overdriven and thus form "hot spots". T…
Gas-liquid stratified MHD flows in inclined rectangular ducts
本研究通过解析与数值方法，分析了倾斜矩形管道中垂直磁场下的气液分层MHD流动，揭示了倾斜、壁面电导率与电磁力对持液率、压力梯度及泵送需求的复杂影响。
Two-phase stratified MHD flows in rectangular ducts
研究双相分层MHD流动特性，揭示非导电气体层对流动对称性的影响及壁导电率配置和磁场取向对流动特性的影响。
Detonation propagation in three-dimensional continuous curved ducts
本文通过三维反应欧拉方程数值模拟，研究了连续弯曲管道中爆轰波的传播，揭示了曲率、截面尺寸和活化能对波结构、模式转变及速度亏损的影响。
Bifurcations and dynamics in inertial focusing of particles in curved rectangular ducts
研究低流速下曲面矩形管道中中性浮力粒子的聚焦动力学，分析粒子尺寸、管道弯曲半径和横截面长宽比对分岔和聚焦过程的影响。
Two-phase stratified MHD flows in wide rectangular ducts: analytical and numerical solutions
本文研究宽矩形管道中气液两相磁流体动力学分层流动，首次发现底壁导电性显著影响速度分布，绝缘底壁时气体润滑和节能效果更佳，并评估了双平板模型在宽管道中的适用性。
We analyse numerically the linear stability of a liquid metal flow in a rectangular duct with perfectly electrically conducting walls subject to a uniform transverse magnetic field. A non-standard three dimensional vector stream function/vorticity formulation is used with Chebyshev collocation method to solve the eigenvalue problem for small-amplitude perturbations. A relatively weak magnetic field is found to render the flow linearly unstable as two weak jets appear close to the centre of the duct at the Hartmann number Ha \approx 9.6. In a sufficiently strong magnetic field, the instability …
We report on a numerical study of axisymmetric flow of liquid metal in a circular duct with rectangular cross-section. The flow is forced through the combination of an axial magnetic field and a radial current. Sweeping a wide range of forcing parameters, we identify the different regimes which characterize the flows and explicit the associate scaling laws. Experimental results are interpreted in the light of our numerical simulations.
The stability of the flow under the magnetic force is one of the classical problems in fluid mechanics. In this paper, the flow in a rectangular duct with different Hartmann (Ha) number is simulated. The finite volume method and the SIMPLE algorithm are used to solve a system of equations and the energy gradient theory is then used to study the (associated) stability of magnetohydrodynamics (MHD). The flow stability of MHD flow for different Hartmann (Ha) number, from Ha=1 to 40, at the fixed Reynolds number, Re=190 are investigated. The simulation is validated firstly against the simulation i…
The dynamics of dilute micron-sized spherical inertial particles in turbulent duct flows is studied by means of direct numerical simulations of the carrier phase turbulence with one-way coupled Lagrangian particles. The geometries are a square and a rectangular duct with width-to-height aspect ratio $AR$ of 3 operating at $Re_{τ,c}=360$ . The present study is designed to determine the effect of turbulence-driven secondary motion on the particle dynamics. Our results show that a weak cross-flow secondary motion significantly changes the cross-sectional map of the particle concentration, mean ve…
Turbulent flows of viscoplastic fluids at high Reynolds numbers have been investigated recently with direct numerical simulations (DNS) but experimental results have been limited. For this reason, we carry out an experimental study of fully turbulent flows of a yield stress fluid in a rectangular aspect ratio channel with a high-resolution laser doppler velocimetry (LDA) setup. We employ aqueous Carbopol solutions, often considered to be a simple yield stress fluid. We formulate different concentrations to address the effect of the rheology of the fluid on the turbulence statistics at an appro…
Soft hydraulics, which addresses the interaction between an internal flow and a compliant conduit, is a central problem in microfluidics. We analyze Newtonian fluid flow in a rectangular duct with a soft top wall at steady state. The resulting fluid--structure interaction (FSI) is formulated for both vanishing and finite flow inertia. At the leading-order in the small aspect ratio, the lubrication approximation implies that the pressure only varies in the streamwise direction. Meanwhile, the compliant wall's slenderness makes the fluid--solid interface behave like a Winkler foundation, with th…
The paper examines the impact of different modelling choices in second-moment closures by assessing model performance in predicting 3-D duct flows. The test-cases (developing flow in a square duct [Gessner F.B., Emery A.F.: {\em ASME J. Fluids Eng.} {\bf 103} (1981) 445--455], circular-to-rectangular transition-duct [Davis D.O., Gessner F.B.: {\em AIAA J.} {\bf 30} (1992) 367--375], and \tsn{S}-duct with large separation [Wellborn S.R., Reichert B.A., Okiishi T.H.: {\em J. Prop. Power} {\bf 10} (1994) 668--675]) include progressively more complex strains. Comparison of experimental data with s…
Dynamics of elastic, nonheavy spheres sedimenting in a rectangular duct
本文通过低雷诺数矩形管道模型实验，揭示弹性非重球体沉降的四阶段动力学及可变形性导致的更高终端速度。
Heat transport in magnetohydrodynamic duct flow regimes with conducting and insulating walls
研究了液态金属在矩形管道段中的流动，考虑横向磁场和侧壁均匀加热，通过直接数值模拟分析不同参数空间下的热传导特性，探讨浮力力对水平和垂直管道流动的影响，并识别四种流动类型以评估其热交换能力。
A conservative coupled finite difference-boundary element computational procedure for the simulation of turbulent magnetohydrodynamic flow in a straight rectangular duct at finite magnetic Reynolds number is presented. The flow is assumed to be periodic in the streamwise direction and is driven by a mean pressure gradient. The duct walls are considered to be electrically insulating. The co-evolution of the velocity and magnetic fields as described respectively by the Navier-Stokes and the magnetic induction equations, together with the coupling of the magnetic field between the conducting doma…
We report a linear scaling law for an electrical voltage as a function of the pressure drop in capillary pipes and ducts. This voltage is generated by a process which is termed spin hydrodynamic generation (SHDG), a result of the collective electron spin--coupling to the vorticity field in the laminar flow in combination with an inverse spin-Hall effect. We study this phenomenon in laminar duct flows with different width-to-height aspect ratios ranging from 1 (square ducts) to infinite (two dimensional channels). First, we analytically solve the governing Valet-Fert spin diffusion equations fo…
Energy stability of magnetohydrodynamic flow in channels and ducts
研究矩形管道中磁流体动力流的能量稳定性，通过切比雪夫展开求解临界雷诺数，发现大纵横比与准二维近似吻合，小纵横比收敛于奥尔结果，并揭示抬升机制主导的线性关系。
This work applies resolvent analysis to incompressible flow through a rectangular duct, in order to identify dominant linear energy-amplification mechanisms present in such flows. In particular, we formulate the resolvent operator from linearizing the Navier--Stokes equations about a two-dimensional base/mean flow. The laminar base flow only has a nonzero streamwise velocity component, while the turbulent case exhibits a secondary mean flow (Prandtl's secondary flow of the second kind). A singular value decomposition of the resolvent operator allows for the identification of structures corresp…
Stratified inclined duct: direct numerical simulations
本文通过首批三维DNS忠实再现SID实验的四种流态，并以较低成本支持长时间模拟，揭示时间与参数变化下的分层湍流转捩。
Inertial particle focusing in fluid flow through spiral ducts: dynamics, tipping phenomena and particle separation
本文将圆形管道粒子动力学模型扩展至曲率缓慢变化的螺旋管道，数值揭示了粒子吸引子分岔引发的丰富非线性动力学与多种临界突变现象，并据此提出非平衡粒径分离新机制。
Linear and nonlinear Granger causality analysis of turbulent duct flows
本文利用POD和线性/非线性格兰杰因果分析研究方管和矩形管湍流相干结构，发现线性机制主导同对称性模态间因果、非线性效应主导对称与反对称模态间因果，并揭示二次流脉动是近壁条带运动的主因。
Realistic sheared flow profile effects on acoustic impedance eduction in small 3D-ducts
研究探讨了真实剪切流对三维矩形风道声传播的影响，指出传统方法在小风道中因速度梯度显著而存在偏差，通过三种流型分析显示均匀或一维流型可近似真实流型，但需正确考虑总马赫数。
Turbulence impacts synthetic methanol production in a square duct flow: a direct numerical simulation (DNS) study
本研究通过直接数值模拟考察方形毫管道内的合成甲醇生产，发现湍流混合可显著提升出口甲醇质量流量，但单程转化效率因停留时间缩短而降低，需权衡反应物循环成本。
Buoyancy-driven exchange flows in inclined ducts
本文通过层化倾斜管道实验系统研究浮力驱动交换流，揭示流态、质量通量和界面厚度对五个无量纲参数的复杂标度律，并提出三类候选模型解释观测结果。
Many practical applications exploit an external local magnetic field -- magnetic obstacle -- as an essential part of their constructions. Recently, it has been demonstrated that the flow of an electrically conducting fluid influenced by an external field can show several kinds of recirculation. The present paper reports a 3D numerical study whose some results are compared with an experiment about such a flow in a rectangular duct.
Effects of the sheared flow velocity profile on impedance eduction in a 2D duct
研究了剪切流速度剖面对二维波导中阻抗提取的影响，发现Ingard-Myers边界条件在二维情况下仍较准确，但简化流剖面可能导致显著偏差。
Longitudinal particle separation
本文研究三维弯曲管道中粒子在主流方向（纵向）的分离，通过椭圆中心线矩形截面管道中周期性变化的曲率诱导SNIPER分岔，实现不同尺寸粒子的纵向聚集与分离。
Inspired by the experiment from Moresco \& Alboussière (2004, J. Fluid Mech.), we study the stability of a liquid metal flow in a rectangular, electrically insulating duct with a steady homogeneous transverse magnetic field. The Lorentz force tends to eliminate velocity variations along the magnetic field, leading to a quasi-two dimensional base flow with Hartmann boundary layers near the walls perpendicular to the magnetic field, and Shercliff layers near the walls parallel to the field. Since the Lorentz force strongly opposes the growth of perturbations with a dependence along the magnetic …
Inertial focusing dynamics of spherical particles in curved microfluidic ducts with a trapezoidal cross-section
研究曲率微流体管道中球形颗粒的惯性聚焦动力学，分析梯形截面对颗粒分离的影响，揭示截面偏转程度与粒子迁移动态的关系，发现拐点分岔现象。
Hydrodynamic irreversibility of non-Brownian suspensions in highly confined duct flow
本研究通过实验和Force Coupling Method模拟，探究了高度受限薄矩形通道内非布朗悬浮液在低雷诺数下的不可逆迁移行为，发现高 confinement 导致颗粒在低体积分数下仍发生显著且快速的向壁面迁移。
The effect of flow confinement on laminar shockwave/boundary-layer interactions
本研究针对矩形管道内马赫2层流激波/边界层相互作用，探究流动约束的影响，发现侧壁使相互作用增强31%，激波发生器长度可调控分离，明确了三维分离拓扑特征及下游流场的关键决定因素。
We analyse numerically the linear stability of the fully developed flow of a liquid metal in a rectangular duct subject to a transverse magnetic field. The walls of the duct perpendicular to the magnetic field are perfectly conducting whereas the parallel ones are insulating. In a sufficiently strong magnetic field, the flow consists of two jets at the insulating walls and a near-stagnant core. We use a vector stream function formulation and Chebyshev collocation method to solve the eigenvalue problem for small-amplitude perturbations. Due to the two-fold reflection symmetry of the base flow t…
Air-driven dynamics of viscoplastic liquid layers
本研究通过长波模型与实验，揭示粘塑性液膜在湍流空气驱动下的局部屈服与波生成机制，导致“吹出”事件，而牛顿薄膜需足够厚才发生类似现象。
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