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Investigation on the vortical structures by the Liutex method in turbulent channels at Re_(τ)=180 with scalloped and triangular riblet control

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Journal of Hydrodynamics 2024年第1期36卷 35-52页

作者： Zhang-dan Yu Shang Jiang Hai-dong Yu Bi-yu Pang Xin Dong yi-qian wang School of Mathematical Sciences Soochow UniversitySuzhou215006China Beijing Institute of Astronautical System Engineering Beijing100076China

Riblets are a series of small protrusions formed along the flow direction,which have been extensively studied as a passive turbulent drag reduction *** and numerical simulations have shown that well-designed riblets can significantly reduce drag in turbulent flows,making them highly promising and valuable for various *** this study,we focus on a scalloped riblet,which is designed by smoothly connecting two third-order polynomials,and thus the sharpness of the tip and the curvature of the valley can be well *** conduct direct numerical simulations of turbulent channel with smooth plate,scalloped riblet-mounted and triangular riblet-mounted *** in wall units of W^(+)=20 and height-width ratio ofγ=0.5 are selected for both riblet *** with the smooth plate case,the scalloped riblet case achieves an 8.68%drag reduction,while the triangular riblet case achieves a 4.79%drag *** obtained drag reduction rate of the triangular riblet is consistent with previous experiments and simulations,and the results indicate that the scalloped riblet is more effective in reducing drag and deserves further *** compare turbulent statistics of the scalloped riblet case with those of the triangular riblet *** mean velocity profiles of riblets are similar,but both the Reynolds shear stress and second-order statistics of velocity fluctuations and Liutex are significantly reduced in the scalloped riblets controlled turbulent channel,indicating that the scalloped riblet can more effectively suppress the spanwise and wall-normal turbulent intensity near the *** also compare the pre-multiplied spectra of streamwise velocity and streamwise Liutex component for the three cases to investigate the energy distribution and characteristics of Liutex *** Liutex vortex identification method is also utilized to analyze the instantaneous flow field,which provides insights into the flow field and could be bene

关键词： Liutex vector riblet drag reduction tip sharpness turbulent channel scalloped

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A letter for objective Liutex

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Journal of Hydrodynamics 2022年第5期34卷 965-969页

作者： yifei Yu yi-qian wang Chaoqun Liu Department of Mathematics University of Texas at ArlingtonArlingtonTexas76019USA School of Mathematical Science Soochow UniversitySuzhou215006China

Vortex structures,detected by the existing popular vortex identification methods,of the same case are generally different if the results are measured by different observers,who are moving with different coordinate *** coordinate systems can be inertial or *** invariance can solve the moving observer problems in different inertial coordinate systems.A variable is invariant under Galilean transformation is called Galilean *** invariant vortex identification methods can provide invariant vortex structures based on different inertial ***,for some situations,the observers are non-inertial,e.g.,the observer is sitting on an aircraft which is accelerating or *** such a situation,it requires to use an objective *** represents a property that one variable is not observer-dependent(the observer’s motion can be either inertial or non-inertial).A strategy based on a zero-vorticity(measured in inertial frame)reference point is proposed in this letter to find the objective vortex *** is chosen as the vortex indicator and two numerical examples are used to test the proposed *** results show that the strategy is effective.

关键词： Objective Liutex vortex structure Galilean invariance

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Preliminary control of the air entrainment in bow wave based on the Liutex force method

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Journal of Hydrodynamics 2022年第3期34卷 483-490页

作者： yi-ding Hu Jian-wei Wu De-cheng Wan Guo wang yi-qian wang Computational Marine Hydrodynamics Lab(CMHL) School of Naval ArchitectureOcean and Civil EngineeringShanghai Jiao Tong UniversityShanghai200240China Wuhan Second Ship Design and Research Institute Wuhan430205China Marine Design and Research Institute of China Shanghai200011China School of Mathematical Science Soochow UniversitySuzhou215006China

Trails induced by air entrainment of bow wave breaking can be observed clearly around an advancing ship,making it prong to be detected and causing reduction in hydrodynamic *** breaking bow wave region,different scale of coherent vortex structures related closely to the air entrainment are *** formation and evolution of bubble clouds can be accounted partly by the swirling vortex flow of the jet *** this work,high-fidelity simulation of the bow wave breaking around a rectangular thin plate is performed with the in-house code BAMR-SJTU.A Liutex force model is constructed to investigate the interaction between the free surface and vortices,and to explore the possibility of alleviating or controlling the air *** study is the first attempt to manipulate vortices corresponding to the air entrainment of the bow wave *** typical vortex structures based on the Liutex vortex identification method and the distribution of the vortex force are *** of the vortex structures and the entrapped bubbles is conducted to illustrate the efficiency of Liutex force model in air entrainment control.

关键词： Bow wave breaking air entrainment coherent vortex structures Liutex force field model

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Numerical study of free end effect of cylinder with low aspect ratios on vortex induced motion

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Journal of Hydrodynamics 2022年第1期34卷 106-115页

作者： Jia-wei He Wei-wen Zhao De-cheng Wan yi-qian wang Computational Marine Hydrodynamics Lab(CMHL) School of Naval ArchitectureOcean and Civil EngineeringShanghai Jiao Tong UniversityShanghai200240China Ocean College Zhejiang UniversityZhoushan316021China School of Mathematical Science Soochow UniversitySuzhou215006China

In this paper,numerical simulation is conducted via our in-house solver,vim-FOAM-SJTU,developed on open-source software,*** around static rigid cylinders and elastically mounted rigid cylinder constrained to free stream with free end are numerically *** significant conclusions are made by analyzing the different results between cases with and without free *** turbulence model is implemented with a shear stress transport-based(SST-based)improved delayed detached eddy simulation(IDDES)approach in the ***,The paper starts with the application of the vim-FOAM-SJTU solver to flow past fixed cylinder with free end at Reynolds number *** numerical results are compared with experimental *** are satisfactory which implies the validity and accuracy of the current computational fluid dynamics(CFD)*** flow visualization in the vicinity of free-end is ***,the solver is utilized to simulate the free end effect associated with the VIM of a cylinder submerged in *** motion responses under different inflow velocities are *** relationship between transverse motion frequency,in-line motion frequency is ***,the effect of the free end on the vortex of the wake field is analyzed by comparing the 3-D vorticity diagrams of the free end *** responses of circular cylinder with or without free end are compared.

关键词： Fluid-structure interaction vim-FOAM-SJTU solver vortex induced motion(VIM) Three-dimensional character

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A Liutex-based subgrid stress model for large-eddy simulation

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Journal of Hydrodynamics 2022年第6期34卷 1145-1150页

作者： Yuan Ding Bi-yu Pang Bo-wen Yan yi-qian wang Yu-xuan Chen Yue-hong qian School of Mathematical Science Soochow UniversitySuzhou215006China Department of Computer Science and Technology Tsinghua UniversityBeijing100084China

The concept of vortex is crucial in both understanding and modeling of *** large eddy simulation(LES),the effect of small-scale eddies onto the large scales or the resolved flow field is modeled by subgrid stress *** though the rotating motions of fluids,i.e.,vortices or eddies are central in developing turbulent models,vortex identification methods are seldom used in these *** this study,we develop a new subgrid model based on the Liutex vector,a new quantity introduced to decompose fluid motions into rigid rotation,pure shear and stretching,and thus identify *** new model is then applied in a decaying homogeneous isotropic turbulence(DHIT)and a turbulent channel flow at Reynolds number Reτ=*** is shown that the new model can predict accurate energy spectra compared with experiments in DHIT and give a well-matched velocity profile in turbulent channel flow without changing the form of the *** directions include improvement of the Liutex based model,for example developing anisotropic subgrid models,and its applications in various turbulent flows.

关键词： Liutex large eddy simulation(LES) subgrid model homogeneous isotropic turbulence turbulent channel flow

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Vortex structures of dynamic pure yaw test using DDES approach and vortex identification method

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Journal of Hydrodynamics 2022年第2期34卷 226-233页

作者： Wei-wen Zhao Qing-jie Meng De-cheng Wan yi-qian wang Computational Marine Hydrodynamics Lab(CMHL) School of Naval ArchitectureOcean and Civil EngineeringShanghai Jiao Tong UniversityShanghai200240China Wuhan Second Ship Design and Research Institute Wuhan430205China School of Mathematical Science Soochow UniversitySuzhou215006China

Considered as the building blocks,vortex structures with variety of sizes and intensity are widely recognized in the viscous flow field around *** this paper,the computational fluid dynamics(CFD)solver,naoe-FOAM-SJTU,coupled with delayed detached-eddy simulation(DDES)is adopted to analyze the vortex structures around the benchmark model Yupeng Ship in dynamic pure yaw tests,which are captured by third generation of vortex identification *** good agreement of the predicted force/moment by DDES method with the experimental data indicates that the present numerical schemes are reliable and *** vortex identification methods,Q-criteria,Ω_(R) and Liutex,are used to capture the vortex structures around the *** large separated flow is able to be investigated by these three methods,in which more vortex structures are captured byΩ_(R) approach and Liutex method with scalar,vector and tensor form seems to be more suitable for analyzing the flow mechanism around the hull in dynamic pure yaw *** general,each vortex structure corresponds to a dominant positive/negative axial Liutex and a bound vortex *** streamlines are spiral in the large separated flow,indicating that the flow in corresponding region is *** the rotation of the flow is not directly related to the intensity of Liutex.

关键词： Dynamic pure yaw test delayed detached-eddy simulation(DDES) vortex identification method vortex structure flow mechanism

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Identification of vortex boundaries in two-dimensional incompressible flows based on the Liutex-shear interaction

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Journal of Hydrodynamics 2023年第5期35卷 825-831页

作者： Bi-yu Pang Zhang-dan Yu Bo-Wen Yan yi-qian wang Chaoqun Liu School of Mathematical Sciences Soochow UniversitySuzhou215006China Department of Computer Science and Technology Tsinghua UniversityBeijing100084China Department of Mathematics University of Texas at ArlingtonArlington76019USA

According to the Liutex-shear decomposition,vorticity can be decomposed into a rotational part,i.e.,the Liutex vector,and a residual shear *** this decomposition,the vorticity transport equation can be used to formulate a governing equation for Liutex easily for two-dimensional incompressible flows with a source term depending on the residual *** dynamics of Liutex-identified structures is then studied in a Taylor-Green vortex flow and a flow past a cylinder at Reynolds number of *** is revealed that such boundaries exist outside which the shear has trivial impact on the evolution of Liutex and inside which enhancing and weakening effects of shear on Liutex can be *** addition,there is a strong dissipation effect upon Liutex on these *** on the interaction mechanism between Liutex and shear,we argue that the vortex boundaries can be identified by these highly dissipative *** contrast,traditional methods use iso-surfaces of arbitrarily selected thresholds to represent vortex *** current method of identifying vortex boundaries based on the Liutex-shear interaction has a clearer theoretical base and avoids the arbitrary selection of *** to three-dimensional incompressible flows can be made in future following the same procedure but with a slightly more complex vorticity transport equation which includes the velocity gradient induced stretching or tilting term.

关键词： Vortex boundary identification Liutex residual shear Taylor-Green vortex cylinder flow

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The homogenous growth of Co-based coordination compound on graphene nanosheet for high-performance K-organic battery and its reaction mechanism

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Rare Metals 2024年第4期43卷 1622-1634页

作者： qian-qian Peng yi-Ting wang Shuo Qi Yao Xiao Yong wang Shuang-qiang Chen School of Environmental and Chemical Engineering Shanghai UniversityShanghai200444China School of Chemistry and Materials Engineering Wenzhou UniversityWenzhou325035China

Metal coordination compounds(MCCs)are gaining popularity for potassium-ion batteries(PIBs)owing to their tuneable structure,multiple reaction sites,low cost and unique ***,they are generally subjected to intrinsic features of the sluggish ionic diffusion coefficient,low electronic conductivity and slow ***,a new MCC material of cobalt-1,3,5-trioxy-2,4,6-triamino-benzo(Co-TB)coordination compound was synthesized and homogenously grown on the surface of graphene nanosheets(GNS),forming a Co-TB@GNS composite with enhanced electronic conductivity and flexible *** from the overall enhanced conductivity,high surface area and abundant activated K-storage sites,Co-TB@GNS electrodes have exhibited superior cycling performance with high reversible capacities(312 mAh·g^(-1)after 100 cycles at 100 mA·g^(-1),224 mAh·g^(-1)after 500 cycles at 1 A·g^(-1))and better rate performances compared with the pure Co-TB compound when served as PIB's ***,multiple in-situ measurement techniques have jointly confirmed that the organic functional groups(C=O,C=N and C=C of benzene rings)and Co^(2+)in Co-TB are the main reversible K-storage sites,including in-situ Fourier transform infrared spectroscopy(FTIR)and X-ray diffraction(XRD),and partial capacity contribution is originated from GNS by the apparent K-storage behavior in the in-situ XRD pattern,proving the possibility of K-storage for metal-organic materials.

关键词： Metal coordination compounds Potassiumion battery Cobalt coordination compound K-storage mechanism

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LEGENDRE-GAUSS-RADAU SPECTRAL COLLOCATION METHOD FOR NONLINEAR SECOND-ORDER INITIAL VALUE PROBLEMS WITH APPLICATIONS TO WAVE EQUATIONS

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Journal of Computational Mathematics 2024年第1期42卷 217-247页

作者： Lina wang qian Tong Lijun yi Mingzhu Zhang Department of Mathematics Shanghai Normal UniversityShanghai 200234China School of Science Henan University of EngineeringZhengzhou 451191China

We propose and analyze a single-interval Legendre-Gauss-Radau(LGR)spectral collocation method for nonlinear second-order initial value problems of ordinary differential *** design an efficient iterative algorithm and prove spectral convergence for the single-interval LGR collocation *** more effective implementation,we propose a multi-interval LGR spectral collocation scheme,which provides us great flexibility with respect to the local time steps and local approximation ***,we combine the multi-interval LGR collocation method in time with the Legendre-Gauss-Lobatto collocation method in space to obtain a space-time spectral collocation approximation for nonlinear second-order evolution *** results show that the proposed methods have high accuracy and excellent long-time *** comparison between our methods and several commonly used methods are also provided.

关键词： Legendre-Gauss-Radau collocation method Second-order initial value problem Spectral convergence Wave equation

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Single-atom Ag-loaded carbon nitride photocatalysts for efficient degradation of acetaminophen:The role of Ag-atom and O_(2)

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Journal of Environmental Sciences 2024年第5期139卷 12-22页

作者： yi Yuan Wen-Long wang Zhi-Wei wang Jin wang qian-Yuan Wu Key Laboratory of Microorganism Application and Risk Control of Shenzhen Guangdong Provincial Engineering Research Center for Urban Water Recycling and Environmental SafetyInstitute of Environment and EcologyShenzhen International Graduate SchoolTsinghua UniversityShenzhen 518055China Shenzhen Environmental Science and New Energy Technology Engineering Laboratory Tsinghua-Berkeley Shenzhen InstituteShenzhen 518055China College of Materials Science and Engineering Shenzhen UniversityShenzhen 518071China

Carbon nitride has been extensively used as a visible-light photocatalyst,but it has the disadvantages of a low specific surface area,rapid electron-hole recombination,and relatively low light *** this study,single-atom Ag was successfully anchored on ultrathin carbon nitride(UTCN)via thermal polymerization,the catalyst obtained is called *** Ag hardly changed the carbon nitride's layered and porous physical *** exhibited efficient visible-light photocatalytic performances in the degradation of various recalcitrant pollutants,eliminations of 85% were achieved by visible-light irradiation for *** with Ag improved the photocatalytic performance of UTCN by narrowing the forbidden band gap from 2.49 to 2.36 e V and suppressing electron-hole pair *** addition,Ag doping facilitated O_(2) adsorption on UTCN by decreasing the adsorption energy from -0.2 to -2.22 e V and favored the formation of O_(2)^(·-).Electron spin resonance and radical-quenching experiments showed that O_(2)^(·-)was the major reactive species in the degradation of Acetaminophen(paracetamol,APAP).

关键词： Ag single atom Carbon nitride Photocatalysis Visible light Adsorption energy Reactive species

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