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Energy transfer channels and turbulence cascade in Vlasov-Maxwell turbulence

Physical Review E 2017年第6期95卷 061201(R)-061201(R)页

作者： Yan Yang W. H. Matthaeus T. N. Parashar P. Wu M. Wan Y. Shi S. Chen V. Roytershteyn W. Daughton State Key Laboratory for Turbulence and Complex Systems Center for Applied Physics and Technology College of Engineering Peking University Beijing 100871 China Bartol Research Institute and Department of Physics and Astronomy University of Delaware Newark Delaware 19716 USA School of Mathematics and Physics Queen's University Belfast BT7 1NN United Kingdom Department of Mechanics and Aerospace Engineering South University of Science and Technology of China Shenzhen Guangdong 518055 China Space Science Institute Boulder Colorado 80301 USA Los Alamos National Laboratory Los Alamos New Mexico 87545 USA

Analysis of the Vlasov-Maxwell equations from the perspective of turbulence cascade clarifies the role of electromagnetic work, and reveals the importance of the pressure-strain relation in generating internal energy. Particle-in-cell simulation demonstrates the relative importance of the several energy exchange terms, indicating that the traceless pressure-strain interaction “Pi-D” is of particular importance for both electrons and protons. The Pi-D interaction and the second tensor invariants of the strain are highly localized in similar spatial regions, indicating that energy transfer occurs preferentially in coherent structures. The collisionless turbulence cascade may be fruitfully explored by study of these energy transfer channels, in addition to examining transfer across spatial scales.

关键词： Plasma turbulence Space & astrophysical plasma

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Energy transfer, pressure tensor and heating of kinetic plasma

arXiv

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arXiv 2017年

作者： Yang, Yan Matthaeus, William H. Parashar, Tulasi N. Haggerty, Colby C. Roytershteyn, Vadim Daughton, William Wan, Minping Shi, Yipeng Chen, Shiyi State Key Laboratory for Turbulence and Complex Systems Center for Applied Physics and Technology College of Engineering Peking University Beijing100871 China Department of Physics and Astronomy University of Delaware NewarkDE19716 United States Space Science Institute BoulderCO80301 United States Los Alamos National Laboratory Los AlamosNM87545 United States Department of Mechanics and Aerospace Engineering South University of Science and Technology of China Shenzhen Guangdong518055 China

Kinetic plasma turbulence cascade spans multiple scales ranging from macroscopic fluid flow to sub-electron scales. Mechanisms that dissipate large scale energy, terminate the inertial range cascade and convert kinetic energy into heat are hotly debated. Here we revisit these puzzles using fully kinetic simulation. By performing scale-dependent spatial filtering on the Vlasov equation, we extract information at prescribed scales and introduce several energy transfer functions. This approach allows highly inhomogeneous energy cascade to be quantified as it proceeds down to kinetic scales. The pressure work, -(P r) u, can trigger a channel of the energy conversion between fluid flow and random motions, which is a collision-free generalization of the viscous dissipation in collisional fluid. Both the energy transfer and the pressure work are strongly correlated with velocity gradients. Copyright © 2017, The Authors. All rights reserved.

关键词： Energy transfer

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Spectral analysis and self-adjusting mechanism for oscillation phenomenon in hydrogen-oxygen continuously rotating detonation engine

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Chinese Journal of Aeronautics 2015年第3期28卷 669-675页

作者： Liu Yusi Wang Yuhui Li Yongsheng Li Yang Wang Jianping Center for Combustion and Propulsion College of Engineering Peking University Center for Applied Physics and Technology Peking University State Key Laboratory for Turbulence & Complex Systems Peking University

Abstract The continuously rotating detonation engine （CRDE） is a new concept of engines for air- craft and spacecraft. Quasi-stable continuously rotating detonation （CRD） can be observed in an annular combustion chamber, but the sustaining, stabilizing and adjusting mechanisms are not yet clear. To learn more deeply into the CRDE, experimental studies have been carried out to inves- tigate hydrogen-oxygen CRDE. Pressure histories are obtained during each shot, which show that stable CRD waves are generated in the combustor, when feeding pressures are higher than 0.5 MPa for fuel and oxidizer, respectively. Each shot can keep running as long as fresh gas feeding main- tains. Close-up of the pressure history shows the repeatability of pressure peaks and indicates the detonation velocity in hydrogen-oxygen CRD, which proves the success of forming a stable CRD in the annular chamber. Spectrum of the pressure history matches the close-up analysis and confirms the CRD. It also shows multi-wave phenomenon and affirms the fact that in this case a single detonation wave is rotating in the annulus. Moreover, oscillation phenomenon is found in pressure peaks and a self-adjusting mechanism is proposed to explain the phenomenon.

关键词： Continuously rotatingdetonation Detonation engines Hydrogen-oxygendetonation Self-adjusting mechanism Spectral analysis

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Effects of the computational domain on the secondary flow in turbulent plane Couette flow

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Chinese physics B 2015年第10期24卷 315-321页

作者：盖杰夏振华蔡庆东 State Key Laboratory of Turbulence and Complex Systems Center for Applied Physics and TechnologyCollege of EngineeringPeking University Department of Aeronautics and Astronautics College of EngineeringPeking University

A series of direct numerical simulations of the fully developed plane Couette flow at a Reynolds number of 6000（based on the relative wall speed and half the channel height h） with different streamwise and spanwise lengths are conducted to investigate the effects of the computational box sizes on the secondary flow（SF）. Our focuses are the number of counter-rotating vortex pairs and its relationship to the statistics of the mean flow and the SF in the small and moderate computational box sizes. Our results show that the number of vortex pairs is sensitive to the computational box size, and so are the slope parameter, the rate of the turbulent kinetic energy contributed by the SF, and the ratio of the kinetic energy of the SF to the total kinetic energy. However, the averaged spanwise width of each counter-rotating vortex pair in the plane Couette flow is found, for the first time, within 4（1 ± 0.25）h despite the domain sizes.

关键词： plane Couette flow the secondary flow large-scale structures vortex pair

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Thermal conductance of one-dimensional materials calculated with typical lattice models

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Physical Review E 2016年第5期94卷 052131-052131页

作者： Chunyi Zhang Wei Kang Jianxiang Wang HEDPS Center for Applied Physics and Technology College of Engineering Peking University Beijing 100871 China State Key Laboratory for Turbulence and Complex Systems Department of Mechanics and Engineering Science College of Engineering Peking University Beijing 100871 China

We show through calculations on typical lattice models that thermal conductance σ can well describe the near-equilibrium thermal transport property of one-dimensional materials of finite length, which presents a situation often met in the application of nanoscale devices. The σ generally contains contributions from the material itself and those from the thermal reservoirs. The intrinsic σ of the material, i.e., the one with the fewest external influences, can be efficiently calculated with the help of the “blackbody”-like nonreflective thermal reservoir, either through the nonequilibrium method or through the Green-Kubo-type formula. σ thus calculated would be helpful to guide the design of thermal management and heat control in nanoscale devices.

关键词： Classical transport

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Scale-to-scale energy transfer in mixing flow induced by the Richtmyer-Meshkov instability

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Physical Review E 2016年第5期93卷 053112-053112页

作者： Han Liu Zuoli Xiao State Key Laboratory for Turbulence and Complex Systems College of Engineering Peking University Beijing 100871 People's Republic of China HEDPS and Center for Applied Physics and Technology College of Engineering Peking University Beijing 100871 People's Republic of China

The Richtmyer-Meshkov instability (RMI) mixing flow induced by a planar shock wave of Mach 1.6 is investigated using direct numerical simulation method. Interfacial perturbations of different scales between air and sulfur hexafluoride are introduced to study the effect of the initial conditions. Focus is placed on the analysis of the scale-to-scale transfer of kinetic energy in both Fourier and physical spaces. The kinetic energy injected from the perturbation scales is transferred to both larger and smaller scales in an average sense within the inner mixing zone (IMZ) at early times and is mainly passed down into smaller scales at the late stage. The physical-space energy flux due to the subgrid-scale (SGS) stress is studied using a filtering approach in order to shed light on the physical origin of the scale-to-scale kinetic energy transfer. It is found that the pointwise SGS energy flux is highly correlated with the local spike and bubble structures in the IMZ. Moreover, it turns out that the mean SGS energy flux is mainly ascribed to the component in the direction of shock wave propagation. An analysis using the method of conditional averaging manifests that the generation of local SGS energy flux is associated with the property of the surrounding flow induced by quadrupolar or dipolar vortex structures.

关键词： Richtmyer-Meshkov instability Shock waves

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Turbulent statistics and flow structures in spanwise-rotating turbulent plane Couette flows

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Physical Review Fluids 2016年第5期1卷 054401-054401页

作者： Jie Gai Zhenhua Xia Qingdong Cai Shiyi Chen Department of Mechanics and Aerospace Engineering South University of Science and Technology of China Shenzhen 518055 China and State Key Laboratory for Turbulence and Complex Systems Center for Applied Physics and Technology College of Engineering Peking University Beijing 100871 China

A series of direct numerical simulations of spanwise-rotating turbulent plane Couette flows at a Reynolds number of 1300 with rotation numbers Ro between 0 and 0.9 is carried out to investigate the effects of anticyclonic rotation on turbulent statistics and flow structures. Several typical turbulent statistics are presented, including the mean shear rate at the centerline, the wall-friction Reynolds number, and volume-averaged kinetic energies with respect to the secondary flow field, turbulent field, and total fluctuation field. Our results show that the rotation changes these quantities in different manners. Volume-averaged balance equations for kinetic energy are analyzed and it turns out that the interaction term acts as a kinetic energy bridge that transfers energy from the secondary flow to the turbulent fluctuations. Several typical flow regimes are identified based on the correlation functions across the whole channel and flow visualizations. The two-dimensional roll cells are observed at weak rotation Ro=0.01, where alternant clustering of vortices appears. Three-dimensional roll cells emerge around Ro≈0.02, where the clustering of vortices shows the meandering and bifurcating behavior. For moderate rotation 0.07≲Ro≲0.36, well-organized structures are observed, where the herringbonelike vortices are clustered between streaks from the top view of three-dimensional flow visualization and form annuluses. More importantly, the vortices are rather confined to one side of the walls when Ro≤0.02 and are inclined from the bottom to upper walls when Ro≥0.07.

关键词： Structure & turbulence of boundary layers turbulence

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Recent progress in compressible turbulence

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Acta Mechanica Sinica 2015年第3期31卷 275-291页

作者： Shiyi Chen Zhenhua Xia Jianchun Wang Yantao Yang State Key Laboratory for Turbulence and Complex Systems Center for Applied Physics and Technology College of Engineering Peking University Physics of Fluids Group Faculty of Science and TechnologyMESA+ Research Institute and J.M.Burgers Centre for Fluid Dynamics University of Twente

In this paper, we review some recent studies on compressible turbulence conducted by the authors＇ group, which include fundamental studies on compressible isotropic turbulence （CIT） and applied studies on developing a con- strained large eddy simulation （CLES） for wall-bounded turbulence. In the first part, we begin with a newly pro- posed hybrid compact-weighted essentially nonoscillatory （WENO） scheme for a CIT simulation that has been used to construct a systematic database of CIT. Using this database various fundamental properties of compressible turbulence have been examined, including the statistics and scaling of compressible modes, the shocklet-turbulence interac- tion, the effect of local compressibility on small scales, the kinetic energy cascade, and some preliminary results from a Lagrangian point of view. In the second part, the idea and for- mulas of the CLES are reviewed, followed by the validations of CLES and some applications in compressible engineering problems.

关键词： Compressible turbulence Hybrid compact-WENO scheme Compressibility effect. Lagrangian studyConstrained large eddy simulation

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Stability and evolution of liquid-gas interfaces on superhydrophobic surfaces

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Advances in Mechanics 2016年第1期46卷 179-225页

作者： Lv, Pengyu Xue, Yahui Duan, Huiling State Key Laboratory for Turbulence and Complex System College of Engineering Peking Universitity Beijing100871 China HEDPS Center for Applied Physics and Technology Peking University Beijing100871 China IFSA Collaborative Innovation Center Shanghai Jiao Tong University Shanghai200240 China

Microstructured superhydrophobic surfaces have broad applications such as anti-fouling and drag reduction. The performance of such surfaces strongly depends on the stability of liquid-gas interfaces, which affects physical processes including wetting transition, restoration and bubble evolution. Various physical factors including pressurization and gas diffusion may destabilize the liquid-air interfaces, and lead to evolution in different manners. In this paper, we first summarize the three types of interfacial stability problems for liquid-gas interfaces. Relying on external stimulations, the liquid-air interface may evolve into different stages and exhibit different morphologies. The recent progress of research on the stability and control of liquid-air interfaces in both droplet systems and submersion circumstances has been reviewed. Based on this review, remaining challenges for future research have been given. © 2016, Chinese Academy of Mechanics. All right reserved.

关键词： Stability

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Constitutive relationship of irradiated metallic materials by eshelby formalism and micro-mechanical scheme

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Journal of Micromechanics and Molecular physics 2016年第3-4期1卷

作者： Yu, Long Chen, Lirong Xiao, Xiazi Chen, Qianying Duan, Huiling State Key Laboratory for Turbulence and Complex Systems Department of Mechanics and Engineering Science College of Engineering Peking University Beijing 100871 China HEDPS Center for Applied Physics and Technology Peking University Beijing 100871 China

In this paper, a theoretical framework including the micro-mechanical method and crystal plasticity model is developed to characterize the macroscopic mechanical behaviors of irradiated metallic materials. At the microscale, a rate-dependent crystal plasticity model is applied to capture the effects of irradiation-induced defects and helium (He) bubbles for individual grains. Then, the micro-mechanical method is adopted to establish the relationship between microscopic individual grains and macroscopic polycrystals. The developed theoretical framework is applied to simulate the mechanical behaviors of neutron irradiated polycrystalline Cu and He implanted Cu/Nb nano-metallic-multilayers (NMMs), and the numerical results match well with corresponding experimental data. © World Scientific Publishing Company.

关键词： Crystal plasticity model Irradiation hardening Micro-mechanical method

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