Table of Content

01 April 2021, Volume 42 Issue 4

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Articles

A new model for dissipative particle dynamics boundary condition of walls with different wettabilities

Yuyi WANG, Jiangwei SHE, Zhewei ZHOU

2021, 42(4):  467-484.  doi:10.1007/s10483-021-2697-9

Abstract ( 1146 )   HTML ( 25)   PDF (2833KB) ( 217 )  

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The implementation of solid-fluid boundary condition has been a major challenge for dissipative particle dynamics (DPD) method. Current implementations of boundary conditions usually try to approach a uniform density distribution and a velocity profile close to analytical solution. The density oscillations and slip velocity are intentionally eliminated, and different wall properties disappear in the same analytical solution. This paper develops a new wall model that combines image and frozen particles and a new strategy to emphasize different wall properties especially wettabilities. The strategy first studies the realistic wall-fluid system by molecular dynamics (MD) simulation depending on physical parameters. Then, a DPD simulation is used to match the density and velocity profiles with the new wall model. The obtained DPD parameters can simulate the systems with the same wall and fluid materials. With this method, a simulation of the Poiseuille flow of liquid argon with copper walls is presented. Other walls with super-hydrophilic, hydrophilic, and hydrophobic wettabilities are also simulated. The limitations of the analytical solution and the effect of the wall-fluid interaction are discussed. The results show that the method suggested in this paper can simulate the mesoscale behavior of the microchannel flow related to realistic systems.

A study of a supersonic capsule/rigid disk-gap-band parachute system using large-eddy simulation

Sheng GONG, Chuijie WU

2021, 42(4):  485-500.  doi:10.1007/s10483-021-2716-5

Abstract ( 654 )   HTML ( 6)   PDF (22653KB) ( 314 )  

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The aerodynamic performances and flow features of the capsule/rigid disk-gap-band (DGB) parachute system from the Mach number 1.8 to 2.2 are studied. We use the adaptive mesh refinement (AMR), the hybrid tuned center-difference and weighted essentially non-oscillatory (TCD-WENO) scheme, and the large-eddy simulation (LES) with the stretched-vortex subgrid model. The simulations reproduce complex interaction of the flow structures, including turbulent wakes and bow shocks, as well as bow shocks and expansion waves. The results show that the calculated aerodynamic drag coefficient agrees well with the previou simulation. Both the aerodynamic drag coefficient and the aerodynamic drag oscillation of the parachute system decrease with the increase of the initial Mach number of the fluid. It is found that the position and angle of the bow shock ahead of the canopy change as the Mach number increases, which makes the flow inside the canopy and the turbulent wake behind the canopy more complex and unstable.

Mechanical effects of circular liquid inclusions inside soft matrix: role of internal pressure change and surface tension

Lei ZHANG

2021, 42(4):  501-510.  doi:10.1007/s10483-021-2722-8

Abstract ( 610 )   HTML ( 4)   PDF (767KB) ( 110 )  

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The mechanical effects of dilute liquid inclusions on the solid-liquid composite are explored, based on an analytical circular inclusion model incorporating the internal pressure change of the liquid and the surface tension of the interface. Several simple explicit dependences of the stress field and effective stiffness on the bulk modulus and the size of the liquid, the surface tension, and Poisson’s ratio of the matrix are derived. The results show that the stresses in the matrix are reduced, and the stiffness of the solid-liquid composite is enhanced with the consideration of either the surface tension or the internal pressure change. Particularly, the effective Young’s modulus predicted by the present model for either soft or stiff matrices agrees well with the known experimental data. In addition, according to the theoretical results, it is possible to stiffen a soft solid by pressured gas with the presence of the surface tension of the solid-gas interface.

Recent improvements of actuator line-large-eddy simulation method for wind turbine wakes

Zhiteng GAO, Ye LI, Tongguang WANG, Shitang KE, Deshun LI

2021, 42(4):  511-526.  doi:10.1007/s10483-021-2717-8

Abstract ( 842 )   HTML ( 3)   PDF (4295KB) ( 189 )  

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In a large wind farm, the wakes of upstream and downstream wind turbines can interfere with each other, affecting the overall power output of the wind farm. To further improve the numerical accuracy of the turbine wake dynamics under atmosphere turbulence, this work proposes some improvements to the actuator line-large-eddy simulation (AL-LES) method. Based on the dynamic k-equation large-eddy simulation (LES), this method uses a precursor method to generate atmospheric inflow turbulence, models the tower and nacelle wakes, and improves the body force projection method based on an anisotropic Gaussian distribution function. For these three improvements, three wind tunnel experiments are used to validate the numerical accuracy of this method. The results show that the numerical results calculated in the far-wake region can reflect the characteristics of typical onshore and offshore wind conditions compared with the experimental results. After modeling the tower and nacelle wakes, the wake velocity distribution is consistent with the experimental result. The radial migration velocity of the tip vortex calculated by the improved blade body force distribution model is 0.32 m/s, which is about 6% different from the experimental value and improves the prediction accuracy of the tip vortex radial movement. The method proposed in this paper is very helpful for wind turbine wake dynamic analysis and wind farm power prediction.

Transport of dissolved oxygen at the sediment-water interface in the spanwise oscillating flow

Kunpeng WANG, Qingxiang LI, Yuhong DONG

2021, 42(4):  527-540.  doi:10.1007/s10483-021-2719-6

Abstract ( 631 )   HTML ( 3)   PDF (15624KB) ( 91 )  

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The distribution and concentration of dissolved oxygen (DO) play important roles in aerobic heterotroph activities and some slow chemical reactions, and can affect the water quality, biological communities, and ecosystem functions of rivers and lakes. In this work, the transport of high Schmidt number DO at the sediment-water interface of spanwise oscillating flow is investigated. The volume-averaged Navier-Stokes (VANS) equations and Monod equation are used to describe the flow in the sediment layer and the sediment oxygen demand of microorganisms. The phase-averaged velocities and concentrations of different amplitudes and periods are studied. The dependence of DO transfer on the amplitude and period is analyzed by means of phase-average statistical quantities. It is shown that the concentration in the sediment layer is positively correlated with the turbulence intensity, and the DO concentration and penetration depth in the sediment layer increases when the period and amplitude of the oscillating flow increase. Moreover, in the presence of oscillating flow, a specific scaling relationship exists between the Sherwood number/oxygen consumption of aerobic heterotrophs and the Reynolds number.

Molybdenum disulfide and magnesium oxide nanoparticle performance on micropolar Cattaneo-Christov heat flux model

M. G. REDDY, S. A. SHEHZAD

2021, 42(4):  541-552.  doi:10.1007/s10483-021-2713-9

Abstract ( 651 )   HTML ( 3)   PDF (1667KB) ( 111 )  

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This article intends to illustrate the Darcy flow and melting heat transmission in micropolar liquid. The major advantage of micropolar fluid is the liquid particle rotation through an independent kinematic vector named the microrotation vector. The novel aspects of the Cattaneo-Christov (C-C) heat flux and Joule heating are incorporated in the energy transport expression. Two different nanoparticles, namely, MoS₂ and MgO, are suspended into the base-fluid. The governing partial differential equations (PDEs) of the prevailing problem are slackening into ordinary differential expressions (ODEs) via similarity transformations. The resulting mathematical phenomenon is illustrated by the implication of fourth-fifth order Runge-Kutta-Fehlberg (RKF) scheme. The fluid velocity and temperature distributions are deliberated by using graphical phenomena for multiple values of physical constraints. The results are displayed for both molybdenum disulphide and magnesium oxide nanoparticles. A comparative benchmark in the limiting approach is reported for the validation of the present technique. It is revealed that the incrementing material constraint results in a higher fluid velocity for both molybdenum disulphide and magnesium oxide nanoparticle situations.

Lattice Boltzmann simulation of phase change and heat transfer characteristics in the multi-layer deposition

Yanlin REN, Zhaomiao LIU, Yan PANG, Xiang WANG, Yuandi XU

2021, 42(4):  553-566.  doi:10.1007/s10483-021-2720-7

Abstract ( 674 )   HTML ( 1)   PDF (1907KB) ( 133 )  

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The metal droplets deposition method (MDDM) is a rapid prototyping technology, implemented via metallurgy bonding within droplets. The anisotropy of heat transfer and re-melting is caused by an asymmetric deposition process. A lattice Boltzmann method (LBM) model is established to predict the heat transfer and phase change in the multi-layer deposition. The prediction model is verified by the experimental temperature profiles in existing literature. The monitoring points are set to compare the temperature profiles, and decoupling analyze the heat transfer mechanism in different positions. The negative relationships between the re-molten volume of the temperature difference, as well as the influence of the dispositive position and the relative position of the adjacent component are observed and analyzed under the heat conduction. This work is helpful to choose the appropriate temperature conditions and the optimal dispositive method.

Non-equilibrium turbulent phenomena in transitional flat plate boundary-layer flows

Feng LIU, Le FANG, Jian FANG

2021, 42(4):  567-582.  doi:10.1007/s10483-021-2728-9

Abstract ( 674 )   HTML ( 2)   PDF (3459KB) ( 91 )  

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Many recent laboratory experiments and numerical simulations support a non-equilibrium dissipation scaling in decaying turbulence before it reaches an equilibrium state. By analyzing a direct numerical simulation (DNS) database of a transitional boundary-layer flow, we show that the transition region and the non-equilibrium turbulence region, which are located in different streamwise zones, present different non-equilibrium scalings. Moreover, in the wall-normal direction, the viscous sublayer, log layer, and outer layer show different non-equilibrium phenomena which differ from those in grid-generated turbulence and transitional channel flows. These findings are expected to shed light on the modelling of various types of non-equilibrium turbulent flows.

Peristaltic flow of a heated Jeffrey fluid inside an elliptic duct: streamline analysis

S. NADEEM, S. AKHTAR, A. SALEEM

2021, 42(4):  583-592.  doi:10.1007/s10483-021-2714-6

Abstract ( 562 )   HTML ( 1)   PDF (2898KB) ( 101 )  

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The peristaltic flow of a heated Jeffrey fluid inside a duct with an elliptic cross-section is studied. A thorough heat transfer mechanism is interpreted by analyzing the viscous effects in the energy equation. The governing mathematical equations give dimensionless partial differential equations after simplification. The final simplified form of the mathematical equations is evaluated with respect to the relevant boundary conditions, and the exact solution is attained. The results are further illustrated by graphs, and the distinct aspects of peristaltic flow phenomena are discussed.

Electro-magneto-hydrodynamic flow of couple stress nanofluids in micro-peristaltic channel with slip and convective conditions

K. RAMESH, M. G. REDDY, B. SOUAYEH

2021, 42(4):  593-606.  doi:10.1007/s10483-021-2727-8

Abstract ( 594 )   HTML ( 2)   PDF (2143KB) ( 73 )  

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This study explores the effects of electro-magneto-hydrodynamics, Hall currents, and convective and slip boundary conditions on the peristaltic propulsion of nanofluids (considered as couple stress nanofluids) through porous symmetric microchannels. The phenomena of energy and mass transfer are considered under thermal radiation and heat source/sink. The governing equations are modeled and non-dimensionalized under appropriate dimensionless quantities. The resulting system is solved numerically with MATHEMATICA (with an in-built function, namely the Runge-Kutta scheme). Graphical results are presented for various fluid flow quantities, such as the velocity, the nanoparticle temperature, the nanoparticle concentration, the skin friction, the nanoparticle heat transfer coefficient, the nanoparticle concentration coefficient, and the trapping phenomena. The results indicate that the nanoparticle heat transfer coefficient is enhanced for the larger values of thermophoresis parameters. Furthermore, an intriguing phenomenon is observed in trapping: the trapped bolus is expanded with an increase in the Hartmann number. However, the bolus size decreases with the increasing values of both the Darcy number and the electroosmotic parameter.