Influence of the second viscosity on the flow propagation

Influence of a chemical reaction on viscous fingering: Effect of the injection flow rate

The hydrodynamic viscous fingering instability can be influenced by a simple viscosity changing chemical reaction of type A+B --> C, when a solution of reactant A is injected into a solution of B and a product C of different viscosity is formed. We investigate here numerically such reactive viscous fingering in the case of a reaction decreasing the viscosity to define the optimal conditions on the chemical and hydrodynamic parameters for controlling fingering. In particular, we analyze the influence of the injection flow rate or equivalently of the Peclet number (Pe) of the problem on the effi…

密度和黏度对湍流中气泡变形、破碎与聚并的影响

Influence of density and viscosity on deformation, breakage, and coalescence of bubbles in turbulence

本文通过相场法直接数值模拟，研究密度比和黏度比对湍流通道流中可变形气泡群破碎与聚并的影响，发现黏度差异作用显著而密度差异影响可忽略，并揭示了气泡内部湍动能的变化规律。

The influence of near-wall density and viscosity gradients on turbulence in channel flows

The influence of near-wall density and viscosity gradients on near-wall turbulence in a channel are studied by means of Direct Numerical Simulation (DNS) of the low-Mach number approximation of the Navier--Stokes equations. Different constitutive relations for density and viscosity as a function of temperature are used in order to mimic a wide range of fluid behaviours and to develop a generalised framework for studying turbulence modulations in variable property flows. Instead of scaling the velocity solely based on local density, as done for the van Driest transformation, we derive an extens…

泰勒-库埃特层流中滑移粘度和应变率粘度：实验反驳与端壁效应

Slip viscosity and strain-rate viscosity in Taylor-Couette laminar flows: Experimental falsification and end-wall effects

本文通过实验和数值模拟验证了滑移粘度模型在泰勒-库埃特层流中的有效性，并揭示了端壁对流场分布的影响。

Viscosity-Stratified Flow in a Hele-Shaw Cell

A hierarchy of mathematical models describing viscosity-stratified flow in a Hele-Shaw cell is constructed. Numerical modelling of jet flow and development of viscous fingers with the influence of inertia and friction is carried out. One-dimensional multi-layer flows are studied. In the framework of three-layer flow the interpretation of the Saffman--Taylor instability is given. A kinematic-wave model of viscous fingering taking into account friction between the fluid layers is proposed. Comparison with calculations on the basis of two-dimensional equations shows that this model allows to dete…

类三次采油微流控实验：黏度比对油簇运移的影响

Tertiary EOR-like microfluidic experiments: influence of viscosity ratio on oil clusters mobilization

本文通过微流控实验研究黏度比对水驱后油簇运移的影响，发现提高注入甘油/水混合物黏度主要通过促使油团破碎为可运移的液滴和油块来显著降低残余油饱和度，并将过程分为油团破碎与油体输运两个阶段。

溶剂粘度比对通道约束圆柱绕流蠕流中粘弹性流体影响的CFD分析

CFD analysis of the influence of solvent viscosity ratio on the creeping flow of viscoelastic fluid over a channel-confined circular cylinder

本文通过CFD数值模拟研究了溶剂粘度比对Oldroyd-B粘弹性流体绕通道约束圆柱蠕流的影响，揭示了不同Deborah数和β值下流场对称性、应力分布及阻力系数的变化规律。

Capillary interactions, aggregate formation and the rheology of particle-laden flows: a lattice Boltzmann study

The agglomeration of particles caused by the formation of capillary bridges has a decisive impact on the transport properties of a variety of at a first sight very different systems such as capillary suspensions, fluidized beds in chemical reactors, or even sand castles. Here, we study the connection between the microstructure of the agglomerates and the rheology of fluidized suspensions using a coupled lattice Boltzmann and discrete element method approach. We address the influence of the shear rate, the secondary fluid surface tension, and the suspending liquid viscosity. The presence of cap…

基于全局稳定性分析对数据驱动雷诺应力闭合误差传播的新解释

New Interpretation for error propagation of data-driven Reynolds stress closures via global stability analysis

本文通过全局稳定性分析研究数据驱动雷诺应力闭合的RANS方程，发现通道流中病态性显著但系统稳定，而周期性山丘分离流中无不稳定特征值却存在数值不稳定性，并揭示了涡粘性分布对稳定性的影响。

From splashing to bouncing: the influence of viscosity on the impact of suspension droplets on a solid surface

We experimentally investigated the splashing of dense suspension droplets impacting a solid surface, extending prior work to the regime where the viscosity of the suspending liquid becomes a significant parameter. The overall behavior can be described by a combination of two trends. The first one is that the splashing becomes favored when the kinetic energy of individual particles at the surface of a droplet overcomes the confinement produced by surface tension. This is expressed by a particle-based Weber number $We_p$. The second is that splashing is suppressed by increasing the viscosity of …

On the influence of fluid rheology on hydraulic fracture

We analyse a problem of a hydraulic fracture driven by a non-Newtonian shear-thinning fluid. Fluid viscosity is described by the four-parameter truncated power-law model. By varying the parameters of the rheological model we investigate spatial and temporal evolution of fluid flow inside the crack and the resulting fracture geometry. A detailed quantitative and qualitative analysis of the underlying physical phenomena is delivered. The results demonstrate that rheological properties of fluids significantly affect the process of hydraulic fracture not only by the values of viscosity, but also b…

Influence of subgrid scale models on the buffer sublayer in channel flow

Subgrid-scale (SGS) models are critical in large-eddy simulations (LES) of turbulent flows. In this paper we conduct a comparative study on different SGS models, including one-k-equation, wall-adapting local eddy-viscosity (WALE), Sigma and shear-constrained model. Wall-resolved LES simulations of channel flows are performed with a finite volume code at shear Reynolds number Re_τ= 395. In the simulations, the buffer sublayer turns out to be the most sensitive to the SGS model. Through the analysis of the mean velocity, the second-order moments, the SGS viscosity and the fluctuating vorticities…

Influence of viscosity on acoustic streaming in sessile droplets: an experimental and a numerical study with a Streaming Source Spatial Filtering (SSSF) method

When an acoustic wave travels in a lossy medium such as a liquid, it progressively transfers its pseudo-momentum to the fluid, which results in a steady acoustic streaming. Remarkably, the phenomenon involves a balance between sound attenuation and shear, such that viscosity vanishes in the final expression of the velocity field. For this reason, the effect of viscosity has long been ignored in acoustic streaming experiments. Here, we show experimentally that the viscosity plays a major role in cavities such as the streaming induced by surface acoustic waves in sessile droplets. We develop a n…

粘性对脉冲生成聚焦射流的影响

Viscous influences on impulsively generated focused jets

针对脉冲生成聚焦射流中自由表面粘性影响研究空白，通过实验与数值模拟揭示切向质量动量传递及粘性对其的作用，提出射流速度预测方程，为相关应用的粘性界面动力学提供新视角。

Effects of Bulk Viscosity in Non-linear Bubble Dynamics

The non-linear bubble dynamics equations in a compressible liquid have been modified considering the effects of compressibility of both the liquid and the gas at the bubble interface. A new bubble boundary equation has been derived, which includes a new term resulted from the liquid bulk viscosity effects. The influence of this term has been numerically investigated considering the effects of water vapor and chemical reactions on the bubble evolution. The results clearly indicate that the new term has an important damping role at the collapse, so that its consideration decreases the amplitude …

Turbulent viscosity variability in self-propelled body wake model

We study the influence of turbulent viscosity variability on the properties of self-propelled body wake model. In addition to the already known integrals of motion obtained with constant turbulent viscosity, we obtain new ones. The presence of new integrals of motion leads, in particular, to changes in the behavior of the width and profile of the wake leading to its conservation.

泰勒弥散在变密度、变粘度脉动流中的表现

Taylor dispersion in variable-density, variable-viscosity pulsatile flows

研究脉动流中变密度和变粘度条件下泰勒弥散现象，通过多重尺度分析建立有效混合模型，揭示剪切诱导弥散机制。

Computations of Nonlinear Propagation of Sound Emitted from High Speed Mixing Layers

Non-linear sound propagation is investigated computationally by simulating compressible time-developing mixing layers using the Large Eddy Simulation (LES) approach and solving the viscous Burgers Equation. The mixing layers are of convective Mach numbers of 0.4, 0.8 and 1.2. The LES results agree qualitatively with known flow behavior. Mach waves are observed in the near sound field of the supersonic mixing layer computed by the LES. These waves show steepening typical to non-linear propagation. Further calculations using the Burgers equation support this finding, where the initial wave slope…

Influence of a thin compressible insoluble liquid film on the eddy currents generated by interacting surface waves

Recently the generation of eddy currents by interacting surface waves was observed experimentally. The phenomenon provides the possibility for manipulation of particles which are immersed in the fluid. The analysis shows that the amplitude of the established eddy currents produced by stationary surface waves does not depend on the fluid viscosity in the free surface case. The currents become parametrically larger being inversely proportional to the square root of the fluid viscosity in the case when the fluid surface is covered by an almost incompressible thin liquid (i.e. shear elasticity is …

The role of second viscosity in the velocity shear-induced heating mechanism

In the present paper we study the influence of second viscosity on non-modally induced heating mechanism. For this purpose we study the set of equations governing the hydrodynamic system. In particular, we consider the Navier Stokes equation, the continuity equation and the equation of state, linearise them and analyse in the context of non-modal instabilities. Unlike previous studies in the Navier Stokes equation we include the contribution of compressibility, thus the second viscosity. By analysing several typical cases we show that under certain conditions the second viscosity might signifi…

不可混溶流体非单调黏度剖面引发黏性指进的线性稳定性分析

Linear stability analysis on the onset of viscous fingering due to a non monotonic viscosity profile for immiscible fluids

针对不可混溶流体在Hele-Shaw单元中非单调黏度剖面引发的黏性指进，理论分析表明界面黏度梯度使界面失稳并促进扰动扩散，并研究了其对色散关系的影响。

Bifurcations and dynamics in convection with temperature-dependent viscosity in the presence of the O(2) symmetry

We focus the study of a convection problem in a 2D setup in the presence of the O(2) symmetry. The viscosity in the fluid depends on the temperature as it changes its value abruptly in an interval around a temperature of transition. The influence of the viscosity law on the morphology of the plumes is examined for several parameter settings, and a variety of shapes ranging from spout to mushroom shaped is found. We explore the impact of the symmetry on the time evolution of this type of fluid, and find solutions which are greatly influenced by its presence: at a large aspect ratio and high Ray…