Mixing of miscible shear-thinning fluids in a lid-driven cavity

The concentration and velocity fields of two refractive index matched miscible shear-thinning fluids in a lid-driven cavity were investigated by using planar laser-induced fluorescence and particle image velocimetry,as well by computational fluid dynamics.Quantitative analyses show that the results obtained by flow simulations with the species transport model are in good agreement with the experimental results.The effects of different parameters were studied by using the intensity of segregation.For two fluids with the same rheological parameters,the relative amounts of liquids H_(1)/H and the power-law index n dominate the mixing process while the Reynolds number Re plays a marginal role.As for two fluids with density difference,buoyancy has significant influence on the mixing process.The dimensionless group Ar/Re(redefined such as to include shear thinning behavior)is proposed for assessing the effect of buoyancy and rheological properties on the mixing of miscible shear-thinning fluids.

Simulating high Reynolds number flow in two-dimensional lid-driven cavity by multi-relaxation-time lattice Boltzmann method

By coupling the non-equilibrium extrapolation scheme for boundary condition with the multi-relaxation-time lattice Boltzmann method, this paper finds that the stability of the multi-relaxation-time model can be improved greatly, especially on simulating high Reynolds number （Re） flow. As a discovery, the super-stability analysed by Lallemand and Luo is verified and the complex structure of the cavity flow is also exhibited in our numerical simulation when Re is high enough. To the best knowledge of the authors, the maximum of Re which has been investigated by direct numerical simulation is only around 50 000 in the literature; however, this paper can readily extend the maximum to 1000 000 with the above combination.

Mixed Convection in a Two-Sided Lid-Driven Square Cavity Filled with Different Types of Nanoparticles:A Comparative Study Assuming Nanoparticles with Different Shapes

Steady,laminar mixed convection inside a lid-driven square cavity filled with nanofluid is investigated numerically.We consider the case where the right and left walls are moving downwards and upwards respectively and maintained at different temperatures while the other two horizontal ones are kept adiabatic and impermeable.The set of nonlinear coupled governing mass,momentum,and energy equations are solved using an extensively validated and a highly accurate finite difference method of fourth-order.Comparisons with previously conducted investigations on special configurations are performed and show an excellent agreement.Meanwhile,attention is focused on the heat transfer enhancement when different nano-particles:Cu,Ag,Al2O3,TiO2 and Fe3O4 are incorporated separately in different base fluids such as:Water,Ethylene-glycol,Methanol and Kerosene oil.In this framework,the numerical results related to several mixtures are presented and concern flow pattern and heat transfer curves for various values of Richardson number[Ri=0.1,1 and 10].It turns out that the choice of the efficient binary mixture for an optimal heat transfer depends not only on the thermophysical properties of the nanofluids but also on the range of the Richardson number.Special attention is devoted to shedding light on the effect of the shape of the nanoparticles on the heat transfer in the case of Water-Ag nanofluid.It is concluded that the spherical shape is more suitable for a better heat transfer enhancement in comparison to the cylindrical ones.

The second Hopf bifurcation in lid-driven square cavity

To date, there are very few studies on the second Hopf bifurcation in a driven square cavity, although there are intensive investigations focused on the first Hopf bifurcation in literature, due to the difficulties of theoretical analyses and numerical simulations. In this paper, we study the characteristics of the second Hopf bifurcation in a driven square cavity by applying a consistent fourth-order compact finite difference scheme recently developed by us. We numerically identify the critical Reynolds number of the second Hopf bifurcation located in the interval of(11093.75, 11094.3604) by bisection. In addition, we find that there are two dominant frequencies in its spectral diagram when the flow is in the status of the second Hopf bifurcation, while only one dominant frequency is identified if the flow is in the first Hopf bifurcation via the Fourier analysis. More interestingly, the flow phase portrait of velocity components is found to make transition from a regular elliptical closed form for the first Hopf bifurcation to a non-elliptical closed form with self-intersection for the second Hopf bifurcation. Such characteristics disclose flow in a quasi-periodic state when the second Hopf bifurcation occurs.

SUPG finite element method based on penalty function for lid-driven cavity flow up to Re = 27500

A streamline upwind/Petrov-Galerkin （SUPG） finite element method based on a penalty function is pro- posed for steady incompressible Navier-Stokes equations. The SUPG stabilization technique is employed for the for- mulation of momentum equations. Using the penalty function method, the continuity equation is simplified and the pres- sure of the momentum equations is eliminated. The lid-driven cavity flow problem is solved using the present model. It is shown that steady flow simulations are computable up to Re = 27500, and the present results agree well with previous solutions. Tabulated results for the properties of the primary vortex are also provided for benchmarking purposes.

Transition to chaos in lid-driven square cavity flow

To date,there are very few studies on the transition beyond second Hopf bifurcation in a lid-driven square cavity,due to the difficulties in theoretical analysis and numerical simulations.In this paper,we study the characteristics of the third Hopf bifurcation in a driven square cavity by applying a consistent fourth-order compact finite difference scheme rectently developed by us.We numerically identify the critical Reynolds number of the third Hopf bifurcation located in the interval of(13944.7021,13946.5333)by the method of bisection.Through Fourier analysis,it is discovered that the flow becomes chaotic with a characteristic of period-doubling bifurcation when the Reynolds number is beyond the third bifurcation critical interval.Nonlinear time series analysis further ascertains the flow chaotic behaviors via the phase diagram,Kolmogorov entropy and maximal Lyapunov exponent.The phase diagram changes interestingly from a closed curve with self-intersection to an unclosed curve and the attractor eventually becomes strange when the flow becomes chaotic.

Polygonal Finite Element for Two-Dimensional Lid-Driven Cavity Flow

This paper investigates a polygonal finite element(PFE)to solve a two-dimensional(2D)incompressible steady fluid problem in a cavity square.It is a well-known standard benchmark(i.e.,lid-driven cavity flow)-to evaluate the numerical methods in solving fluid problems controlled by the Navier-Stokes(N-S)equation system.The approximation solutions provided in this research are based on our developed equal-order mixed PFE,called Pe1Pe1.It is an exciting development based on constructing the mixed scheme method of two equal-order discretisation spaces for both fluid pressure and velocity fields of flows and our proposed stabilisation technique.In this research,to handle the nonlinear problem of N-S,the Picard iteration scheme is applied.Our proposed method’s performance and convergence are validated by several simulations coded by commercial software,i.e.,MATLAB.For this research,the benchmark is executed with variousReynolds numbers up to the maximum Re=1000.All results then numerously compared to available sources in the literature.

Mixed convection characteristics in lid-driven cavity containing heated triangular block

This research work numerically analyzes 2D,steady state,mixed convective heat transfer for Newtonian fluids in lid driven square enclosure with centered triangular block（blockage—10%or 30%）maintained either at the constant wall temperature or constant heat flux thermal conditions.The fluid flow in the enclosure is initiated by top moving wall in＋x-direction,while all other walls are stationary.The top and bottom walls are thermally insulated.In particular,the governing field equations are solved for range of governing parameters such as,Reynolds number（1–1000）,Prandtl number（1–100）,and Grashof number

Hydrodynamic Mixed Convection in a Lid-Driven Hexagonal Cavity with Corner Heater

Hydrodynamic mixed convection in a lid-driven hexagonal cavity with corner heater is numerically simulated in this paper by employing finite element method. The working fluid is assigned as air with a Prandtl num-ber of 0.71 throughout the simulation. The left and right walls of the hex-agonal cavity are kept thermally insulated and the lid moves top to bottom at a constant speed U0. The top left and right walls of the enclosure are maintained at cold temperature Tc. The bottom right wall is considered with a corner heater whereas the bottom remaining part is adiabatic and inside the cavity a square shape heated block Th. The focus of the work is to investigate the effect of Hartmann number, Richardson number, Grashof number and Reynolds number on the fluid flow and heat transfer characteristics inside the enclosure. A set of graphical results is presented in terms of streamlines, isotherms, local Nusselt number, velocity profiles, temperature profiles and average Nusselt numbers. The results reveal that heat transfer rate increases with increasing Richardson number and Hartmann number. It is also observed that, Hartmann number is a good control parameter for heat transfer in fluid flow in hexagonal cavity.

Numerical Investigation of Lid-Driven Deep Cavity with Local Grid Refinement of MRT-LBM

In the case of lid-driven deep cavity flow, the effects of different resolutions of local grid refinement have been studied in the frame of multiple relaxation times (MRT) lattice Boltzmann method (LBM). In all the cases, the aspect ratio and Reynolds number are set as 1.5 and 3.200, respectively. First, the applied method is validated by comparing it with two reported works, with which agreements are reached. Then, six separate degrees of local grid refinement at the upper left corner, i.e. purely coarse grid, including 1/64, 1/32, 1/16, 1/8, 1/4 refinements of the lattice number in the width direction have been studied in detail. The results give the following indications:① The refinement degrees lower than 1/8 produce similar results;② For single corner refinement, 1/4 refinement is adequate for clearing the noises in the singularity zone to a large extent;③ New noise around the interface between coarse and fine zones are introduced by local grid refinement. Finally, refinement of entire subzone neighboring the lid is examined to avoid introducing new noises and it has been found effective.

Mixed Convection of Bingham Fluid in a Two Sided Lid-Driven Cavity Heated From Below

This study aims to analyze mixed convection in a square cavity with two moving vertical walls by finite volume method.The cavity filled with Non-Newtonian fluid of Bingham model is heated from below and cooled by the other walls.This study has been conducted for certain parameters of Reynolds number(Re=1-100),Richardson number(Ri=1-20),Prandtl number(Pr=1-500),and Bingham number has been studied from 0 to 10.The results indicate that the increase in yield stress drops the heat transfer and the flow become flatter,while increasing Reynolds number augments it.The convective transport is dominant when increasing Richardson number which leads to enhance heat transfer in the cavity for both Newtonian and Non-Newtonian fluid.A correlation of Nusselt number is given in function of different parameters.

Bifurcation of Bingham Streamline Topologies in Rectangular Double-Lid-Driven Cavities

Numerical simulation of the bifurcation of Bingham fluid streamline topologies in rectangular double-lid-driven cavity, with varying aspect (height to width) ratio A, is presented. The lids on the top and bottom move at the same speed but in opposite directions so that symmetric flow patterns are generated. Similar to the Newtonian case, bifurcations occur as the aspect ratio decreases. Special to Bingham fluids, the non-Newtonian indicator, Bingham number B, also governs the bifurcation besides the bifurcation parameter A.

Mixed Convection Heat Transfer for Nanofluids in a Lid-Driven Shallow Rectangular Cavity Uniformly Heated and Cooled from the Vertical Sides:The Opposing Case

An investigation on flow and heat transfer due to mixed convection, in a lid-driven rectangular cavity filled with Cu- water nanofluids and submitted to uniform heat flux along with its vertical short sides, has been conducted numerically by solving the full governing equations with the finite volume method and the SIMPLER algorithm. In the case of a slender enclosure, these equations are considerably reduced by using the parallel flow concept. Solutions, for the flow and temperature fields, and the heat transfer rate, have been obtained depending on the governing parameters, which are the Reynolds, the Richardson numbers and the solid volume fraction of nanoparticles. A perfect agreement has been found between the results of the two approaches for a wide range of the abovementioned parameters. It has been shown that at low and high Richardson numbers, the convection is ensured by lid and buoyancy-driven effects, respectively, whereas between these extremes, both mechanisms compete. Moreover, the addition of Cu-nanoparticles, into the pure water, has been seen enhancing and degrading heat transfer by lid and buoyancy-driven effects, respectively.

Numerical Investigation of a Mixed Convection Flow in a Lid-Driven Cavity

This study is devoted to the computational fluid dynamics (CFD) modeling of steady laminar mixed convection flow and heat transfer in lid driven cavity (10 ≤ Re ≤ 1000). The ratio of the height to the width of the cavity is ranged over H/L = 0.5 to 1.5. The governing equations are solved using commercial finite volume package FLUENT to visualize the nature of the flow and estimate the heat transfer inside the cavity for different aspect ratio. The simulation results are presented in terms of average Nusselt number of the hot wall, velocity profile, and temperature contours. It was found that the average Nusselt number inside the cavity is strongly governed by the aspect ratio as well as the Reynolds number. A parametric study is conducted to demonstrate the effect of aspect ratio on the flow and heat transfer characteristics. It is found that heat transfer enhancement was obtained by decreasing the aspect ratio and/or increasing the Reynolds number.

Numerical Examination of a Cavity Containing Nanofluid with an Upper Oscillating Wall and Baffle

The cavity with lid-driven is greatly used in mixing,coating,and drying applications and is a substantial issue in the study of thermal performance rate and fluid field.A numerical approach is presented to study the thermal distribution and passage of fluid in a lid-driven cavity with an upper oscillating surface and an attached baffle.The walls of a cavity at the left and right were maintained at 350 and 293 K,respectively.The upper oscillating surface was equipped with a variable height to baffle to increase the convection of the three kinds of TiO_(2),Al_(2)O_(3),andCuO nanofluids with various of 0.4,0.8,and 0.4,0.8,and 1.2 vol.%in volume fractions.It was found that using a baffle attached to the oscillating upper surface of the cavity will lead to improving the distribution of vorticity in the cavity and increase the stream in the cavity.Also,increasing the baffle height,oscillating velocity,and volume fraction of nanoparticles contributes to enhancing the Nusselt number values by 50%for increasing baffle height from h∗=0.1 to 0.1.Also,the Nu improved by 20%for increasing oscillating velocity from w=05 to 20 rad/s and by 12%for using Al_(2)O_(3)nanofluid instead of TiO3 atϕ=0.8 vol.%.

幂律流体顶盖驱动流中的颗粒运动

采用扩散界面格子Boltzmann模型研究了圆形颗粒在幂律流体方腔流中的运动,重点分析了初始位置、幂律指数、颗粒大小对圆形颗粒在幂律流体顶盖驱动流中的运动的影响.数值结果表明不同初始位置的圆形颗粒最终均能稳定在极限环上运动.不同幂律指数的幂律流体对圆形颗粒运动的极限环有明显影响,对于剪切增稠流体,颗粒的运动速度明显增大,极限环半径明显缩小;对于剪切稀化流体,左下角和右下角的次级涡收缩,极限环向方腔的右下角移动.圆形颗粒较小时,颗粒的运动速度较快,运动半径较大,运动轨迹更接近流体的流线;圆形颗粒较大时,受到边界的限制,极限环半径较小,运动速度较慢.此外,还讨论了颗粒对顶盖驱动流主涡涡心位置的影响,颗粒会将主涡涡心推向远离颗粒的方向.

Combined effect of Reynolds and Grashof numbers on mixed convection in a lid-driven T-shaped cavity filled with water-Al_2O_3 nanofluid

Lid-driven mixed convection has been given immense importance due to its wide range of applications. A T-shaped cavity is introduced and pertinent parameters controlling mixed convection phenomenon are analyzed in this paper. Water-Al2O3 nanofluid is considered inside the cavity to augment heat transfer rate. Galerkin weighted residual method of finite element analysis is applied for the numerical simulations. Numerical solution is obtained for different solid volume fractions of nanofluid（？= 0- 0.15）, Grashof numbers（Gr= 0.1 ？5 000） and Reynolds numbers（Re= 0.31 ？1 000） in laminar flow regime. Special attention is given on the analysis of flow at the pure mixed convection regime. It is found that Grashof, Reynolds and Richardson numbers along with solid volume fraction of nanofluid have significant effect on heat transfer characteristics inside the cavity. Results are presented using streamline and isotherm contours along with related variation of average Nusselt numbers of the heated wall and average fluid temperature inside the cavity.

Mixed convection in a lid-driven cavity filled with single and multiple-walled carbon nanotubes nanofluid having an inner elliptic obstacle

In this study,numerical analysis and optimization in a single and multiple walled carbon nanotube-water nanofluid filled lid driven cavity having an inner elliptic obstacle were performed by using finite element method and COBYLA optimization solver.The top wall is moving with constant speed and vertical walls are kept at constant temperatures.An optimal size of the inner elliptic obstacle was determined by using an optimization study to maximize the average heat transfer along the hot wall of the cavity.Numerical simulation was performed by for various values of Richardson numbers(between 0.05 and 50)and various solid particle volume fraction(between 0 and 0.06)for single and multiple-walled carbon nanotubes water nanofluid.A larger obstacle(higher values of radii in the major and minor axis)with lower values of Richardson number results in higher heat transfer rates.The average Nusselt number versus solid particle volume fraction shows a linear trend and the discrepancy between the average Nusselt number for the cavity with the optimized obstacle and other obstacles becomes higher with higher particle volume fraction.The average heat transfer enhances significantly which is about 120.20%for single wall carbon nanotube-water nanofluid at solid volume fraction of 0.06 when compared to pure water.The discrepancy between the average Nusselt number for single and multiple walled carbon nanotubes becomes higher for higher values of Richardson number and solid particle volume fraction.A polynomial type correlation was proposed for the average Nusselt number along the hot wall which is fifth order for Richardson number an first order for nanoparticle volume fraction.

Numerical research on lid-driven cavity flows using a three-dimensional lattice Boltzmann model on non-uniform meshes

A lattice Boltzmann model combined with curvilinear coordinate is proposed for lid-driven cavity three-dimensional (3D) flows. For particle velocity distribution, the particle collision process is performed in physical domain, and the particle streaming process is carried out in the corresponding computational domain, which is transferred from the physical domain using interpolation method. For the interpolation calculation, a second-order upwind interpolation method is adopted on internal lattice nodes in flow fields while a second-order central interpolation algorithm is employed at neighbor-boundary lattice nodes. Then the above-mentioned model and algorithms are used to numerically simulate the 3D flows in the lid-driven cavity at Reynolds numbers of 100, 400 and 1000 on non-uniform meshes. Various vortices on the x-y, y-z and x-z symmetrical planes are successfully predicted, and their changes in position with the Reynolds number increasing are obtained. The velocity profiles of u component along the vertical centerline and w component along the horizontal centerline are both in good agreement with the data in literature and the calculated results on uniform meshes. Besides, the velocity vector distributions on various cross sections in lid-driven cavity predicted on non-uniform meshes are compared with those simulated on uniform meshes and those in the literature. All the comparisons and validations show that the 3D lattice Boltzmann model and all the numerical algorithms on non-uniform meshes are accurate and reliable to predict effectively flow fields.

Chaotic Lid-Driven Square Cavity Flows at Extreme Reynolds Numbers

This paper investigates the chaotic lid-driven square cavity flows at extreme Reynolds numbers.Several observations have been made from this study.Firstly,at extreme Reynolds numbers two principles add at the genesis of tiny,loose counterclockwise-or clockwise-rotating eddies.One concerns the arousing of them owing to the influence of the clockwise-or counterclockwise currents nearby;the other,the arousing of counterclockwise-rotating eddies near attached to the moving(lid)top wall which moves from left to right.Secondly,unexpectedly,the kinetic energy soon reaches the qualitative temporal limit’s pace,fluctuating briskly,randomly inside the total kinetic energy range,fluctuations which concentrate on two distinct fragments:one on its upper side,the upper fragment,the other on its lower side,the lower fragment,switching briskly,randomly from each other;and further on many small fragments arousing randomly within both,switching briskly,randomly from one another.As the Reynolds number Re→∞,both distance and then close,and the kinetic energy fluctuates shorter and shorter at the upper fragment and longer and longer at the lower fragment,displaying tall high spikes which enlarge and then disappear.As the time t→∞(at the Reynolds number Re fixed)they recur from time to time with roughly the same amplitude.For the most part,at the upper fragment the leading eddy rotates clockwise,and at the lower fragment,in stark contrast,it rotates counterclockwise.At Re=109 the leading eddy-at its qualitative temporal limit’s pace—appears to rotate solely counterclockwise.