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Effect of the Coulomb and dielectric forces on the onset of Rayleigh-Bénard convection

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Acta Mechanica Sinica 2024年第6期40卷 64-77页

作者： Zhonglin Du Pedro A.Vázquez Jian Wu School of Energy Science and Engineering Harbin Institute of TechnologyHarbin150001China Heilongjiang Key Laboratory of Micro-and Nano-scale fluid Flow and heat transfer Harbin150001China Departamento de Física Aplicada III ETSIIUniversidad de SevillaSevilla41092Spain

In this paper,the effect of Coulomb and dielectric forces on the onset of Rayleigh-Bénard convection(RBC)in a dielectric liquid layer contained between two parallel electrode plates has been numerically *** different operating conditions have been considered in electrohydrodynamic(EHD)conduction:ohmic and saturation,and variations in the physical properties of the dielectric fluid with *** electric equations and the state equations based on the Boussinesq approximation are integrated in the framework of OpenFOAM buoyantBoussinesqPimpleFoam *** results show that in the ohmic regime,the combined effect of Coulomb and dielectric forces promotes the onset of RBC flow,while in the saturation state,the inhibition of RBC flow by Coulomb force is more *** value of the critical Rayleigh number Ra decreases with increasing electric Reynolds number ReE in the ohmic regime,whereas in the saturation state,the critical Ra increases with increasing *** the saturation regime,the flow field always has a steady flow in the range of parameters ***,the onset of the RBC flow promoted by the dielectric force is more pronounced in the ohmic *** to the presence of the dielectric force,the flow field exhibits periodic oscillatory flow at low electric Reynolds numbers for the range of parameters considered.

关键词： EHD conduction Dielectric force Rayleigh-Bénard convection OpenFOAM

Geometric Constraints for Global Regularity of 3D Shear Thickening fluids

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Acta Mathematicae Applicatae Sinica 2024年第1期40卷 205-210页

作者： Jia-qi Yang Research&Development institute of Northwestern Polytechnical University in Shenzhen Shenzhen518063China Key Laboratory for mechanics in fluid Solid Coupling Systems Institute of MechanicsChinese Academy of SciencesBeijing100190China

We consider the relation between the direction of the vorticity and the global regularity of 3D shear thickening *** is showed that a weak solution to the non-Newtonian incompressible fluid in the whole space is stron... 详细信息

关键词： direction of the vorticity non-Newtonian fluid global regularity

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Passive particles driven by self-propelled particle:The wake effect

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Chinese Physics B 2024年第4期33卷 500-507页

作者：郑凯选汪静文王世锋聂德明 institute of fluid mechanics China Jiliang UniversityHangzhou 310018China Department of Mechanical Engineering Hangzhou Vocational&Technical CollegeHangzhou 310018China

This work focuses on numerically studying hydrodynamic interaction between a passive particle and a self-propelled particle,termed a squirmer,by using a two-dimensional lattice Boltzmann method(LBM).It is found that the squirmer can capture a passive particle and propel it simultaneously,provided the passive particle is situated within the squirmer's *** research shows that the critical capture distance,which determines whether the particle is captured,primarily depends on the intensity of the squirmer's *** stronger dipolarity of squirmer results in an increased critical capture ***,the Reynolds number is found to have minimal influence on this ***,the passive particle,when driven by the squirmer's wake,contributes to a reduction in the squirmer's *** results in a mutual acceleration for both *** findings can provide valuable perspectives for formulating the principles of reducing the drag of micro-swimmers and help to achieve the goal of using micro-swimmers to transport goods without physical tethers.

关键词： lattice Boltzmann method(LBM) self-propelled particles particle-laden flow

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Swimming velocity of spherical squirmers in a square tube at finite fluid inertia

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Applied Mathematics and mechanics(English Edition) 2024年第9期45卷 1481-1498页

作者： Tongxiao JIANG Deming NIE Jianzhong LIN institute of fluid mechanics China Jiliang UniversityHangzhou 310008China Key Laboratory of Impact and Safety Engineering(Ningbo University) Ministry of EducationNingbo 315211China institute of fluid Engineering Zhejiang UniversityHangzhou 310027China

The three-dimensional lattice Boltzmann method(LBM)is used to simulate the motion of a spherical squirmer in a square tube,and the steady motion velocity of a squirmer with different Reynolds numbers(Re,ranging from 0.1 to 2)and swimming types is investigated and analyzed to better understand the swimming characteristics of microorganisms in different ***,as the Reynolds number increases,the effect of the inertial forces becomes significant,disrupting the squirmer's ability to maintain its theoretical ***,as the Reynolds number increases,the structure of the flow field around the squirmer changes,affecting its velocity of ***,the swimming velocity of the squirmer exhibits a quadratic relationship with the type of swimming and the Reynolds ***,the narrow tube exerts a significant inhibitory effect on the squirmer *** addition,although chirality does not directly affect the swimming velocity of the squirmer,it can indirectly affect the velocity by changing its motion mode.

关键词： spherical squirmer swimming characteristics swimming velocity fow structure

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Mechanical responses and crystal plasticity model of CoCrNi medium-entropy alloy under ramp wave compression

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Matter and Radiation at Extremes 2024年第5期9卷 93-108页

作者： Jinlei Dong Xuping Zhang Guiji Wang Xianqian Wu Binqiang Luo Xuemiao Chen Fuli Tan Jianheng Zhao Chengwei Sun institute of fluid Physics China Academy of Engineering PhysicsMianyang 621999China institute of mechanics Chinese Academy of SciencesBeijing 100190China institute of Applied Electronics China Academy of Engineering PhysicsMianyang 621999China

It is of substantial scientific significance and practical value to reveal and understand the multiscale mechanical properties and intrinsic mechanisms of medium-entropy alloys(MEAs)under high strain rates and *** this study,the mechanical responses and deformation mechanisms of an equiatomic CoCrNi MEA are investigated utilizing magnetically driven ramp wave compression(RWC)with a strain rate of 105 s^(−1).The CoCrNi MEA demonstrates excellent dynamic mechanical responses and yield strength under RWC compared with other advanced *** characterizations reveal that grain refinement and abundant micromechanisms,including dislocation slip,stacking faults,nanotwin network,and Lomer–Cottrell locks,collectively contribute to its excellent performance during ***,dense deformation twins and shear bands intersect,forming a weave-like microstructure that can disperse deformation and enhance *** the basis of these observations,we develop a modified crystal plasticity model with coupled dislocation and twinning mechanisms,providing a relatively accurate quantitative description of the multiscale behavior under *** results of simulations indicate that the activation of multilevel microstructures in CoCrNi MEA is primarily attributable to stress inhomogeneities and localized strain during *** research offers valuable insights into the dynamic mechanical responses of CoCrNi MEA,positioning it as a promising material for use under extreme dynamic conditions.

关键词： deformation alloy microstructure

Decohesion of graphene from a uniaxially-stretched substrate:Failure analysis of a frictional adhesive interface

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Friction 2024年第3期12卷 510-521页

作者： Bo PENG Chaochen XU Qingao WANG Pei ZHAO Xiqiao FENG Qunyang LI AML Department of Engineering MechanicsTsinghua UniversityBeijing 100084China State Key Laboratory of Tribology in Advanced Equipment Tsinghua UniversityBeijing 100084China Center for X-mechanics and institute of Applied mechanics Zhejiang UniversityHangzhou 310027China State Key Laboratory of fluid Power and M

Composite structures consisting of two-dimensional(2D)materials deposited on elastic substrates have a wide range of potential applications in flexible *** such devices,robust 2D film/substrate interfacial adhesion is essential for their reliable performance when subjected to external thermal and mechanical *** better understand the strength and failure behavior of the 2D film/substrate interfaces,two types of graphene/polymer samples with distinct interfacial adhesion properties are fabricated and tested by uniaxially stretching the *** on the interfacial adhesion,two drastically different debonding rates are observed,i.e.,rapid snap-through debonding and more progressive crack *** by the experimental observation,we propose an improved shear-lag model with a trapezoidal-shaped cohesive zone to derive an analytical solution for the decohesion *** theoretical model reveals that the decohesion behavior of the frictional adhesive interface is governed by three dimensionless ***,the dimensionless length of the film essentially determines the decohesion rate;while the other two parameters affect the critical substrate strain to initiate *** fitting the experimental data with the theoretical model,the intrinsic adhesion properties of the two samples are obtained with physically meaningful *** work offers an analytical solution to describing the decohesion behavior of general thin film/substrate systems with a frictional adhesive interface,which is beneficial for characterizing and optimizing the mechanical properties of various thin film/polymer devices.

关键词： film/substrate systems adhesion frictional sliding interface decohesion cohesive-zone model

Statistics and dynamics of coherent structures in compressible wall-bounded turbulence

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Science China(Physics,mechanics & Astronomy) 2024年

作者： Ming Yu SiWei Dong XianXu Yuan ChunXiao Xu State Key Laboratory of Aerodynamics Key Laboratory of Applied mechanics Institute of Fluid Mechanics Department of Engineering Mechanics Tsinghua University

Compressible wall-bounded turbulence is ubiquitously encountered in modern aerospace and mechanical industries. In this review, we summarize the current state of the literature on the flow physics of compressible wall-bounded turbulence with simple flow geometry and boundary constraints, focusing on the statistics and dynamics of coherent structures, the seemingly organized flow patterns hidden amidst the nonlinear chaotic random processes. We summarize the conclusions brought by recent year studies regarding the influences of the Mach number and wall temperature on the velocity streaks, quasi-streamwise vortices and dilatational motions in the near-wall region, and the large-scale and very-large-scale motions in the outer region, from both statistical and dynamical point of view, with the primary concern of the similarities with and disparities from those in incompressible flows.

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Channel Flows in Plate heat Exchangers with the Aid of Particle Tracking Velocimetry

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Open Journal of fluid Dynamics 2024年第3期14卷 163-183页

作者： Felipe José dos Santos Leonel Edward Beckedorff Kleber Vieira de Paiva Jorge Luiz Goes Oliveira PETROBRASPetrleo Brasileiro S.A. Rio de Janeiro Brazil institute of fluid mechanics and heat transfer Technische Universitt Wien Vienna Austria Department of Mobility Engineering Federal University of Santa Catarina Joinville Brazil

Channel flows of Plate heat Exchangers (PHEs) were assessed by experiments with three different chevron angle arrangements in turbulent regime. Two chevron angles were selected to assess low and high pressure drop channels, besides a third mixed configuration as to achieve in-between results regarding hydraulic performance. Friction factor correlations were provided with the channel Reynolds number ranging from 1175 to 8325. Two-dimensional (2D) mean velocity field was obtained by Particle Tracking Velocimetry (PTV) with Reynolds number equal to 3450. To the best of our knowledge, this is the first experimental study that quantified the complete 2D velocity field of a typical PHE channel. This value allowed comparison with literature results of Plate and Shell heat Exchanger (PSHE) channels with the same Reynolds number. PSHE mean velocity field is highly heterogeneous as compared to the one obtained for PHE channels. Peak velocity magnitude in the PSHE center is 50% higher than its bulk velocity, whereas this value is only 15% higher in the PHE center. Pressure drop in PHE mixed channels cannot be approximated by averaging chevron angles: furrow flow prevailed in the specified conditions. The axial velocity is asymmetric regarding the vertical plane. Smooth streamlines prevail in the channel inlet. Recirculation zones at the channel exit affect pipe flow in the manifold outlet with swirling flow structures. The necessary length to obtain fully developed pipe flow at the channel outlet was estimated. Significant velocity components occur in the distribution areas and can limit the heat exchanger performance. The results reported herein are essential to understand how the PHE channel geometry affects the velocity field and, therefore, local heat transfer and dissipation processes.

关键词： PHE PTV PSHE Friction Factor Chevron

A dispersion-based impact identification method:mechanical model and experimental verification

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Acta Mechanica Sinica 2024年第7期40卷 80-91页

作者： Zishang Liu Tianyu Chen Kun Zhang Yanpeng Wei Yacong Guo Bingchen Wei Key Laboratory of Microgravity(National Microgravity Laboratory) Institute of MechanicsChinese Academy of SciencesBeijing 100190China Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of SciencesBeijing 100049China School of Engineering Science University of Chinese Academy of SciencesBeijing 100049China Key Laboratory for mechanics in fluid Coupling Systems Institute of MechanicsChinese Academy of SciencesBeijing 100190China

External transient impact loads widely exist in the service environment of various engineering structures,and urgent engineering and military application requirements call for research on the theory and method of impact *** manuscript proposes a method to identify the impact *** employing the dispersive property of wave propagation through the waveguides,a dispersion-based average power spectral density(PSD)curve for quantitative representation of the dispersion is established,and its evolution law is investigated to apply the identification of impact *** critical parameters of the average PSD curve are obtained by analyzing the response of the structure from the perspective of *** effectiveness of this method is verified through the development of the triple-successive-impact split Hopkinson bar and the triple-successive-impact *** the method proposed in this manuscript,a kind of impact identification under multiple impact loads,which is not convenient to measure directly by the sensor,is realized,especially in the case of highly transient external impact.

关键词： Structural impact Dispersion Structure vibration Waveguides Impact identification