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Effect of perforation on flow past a conic cylinder at Re =100: wavy vortex and sign laws

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Acta Mechanica Sinica 2018年第5期34卷 812-829页

作者： l.M.lin x.f.Zhong Y.x.Wu Key laboratory for Mechanics in fluid Solid Coupling Systems Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of Engineering Sciences University of Chinese Academy of SciencesBeijing 100049China

In order to find the intrinsic physical mechanism of the original Kármán vortex wavily distorted across the span due to the introduction of three-dimensional (3-D) geometric disturbances,a flow past a peak-perforated conic shroud is numerically simulated at a Reynolds number of *** on previous work by Meiburg and lasheras (1988),the streamwise and vertical interactions with spanwise vortices are introduced and *** vortex-shedding patterns in the near wake for different flow regimes are reinspected and illustrated from the view of these two ***,in regime Ⅰ,spanwise vortices are a little distorted due to the weak *** in regime Ⅱ,spanwise vortices,even though curved obviously,are still shed synchronously with moderate streamwise and vertical *** in regime Ⅲ,violently wavy spanwise vortices in some vortex-shedding patterns,typically an Ω-type vortex,are mainly attributed to the strong vertical interactions,while other cases,such as multiple vortex-shedding patterns in sub-regime Ⅲ-D,are resulted from complex streamwise and vertical interactions.A special phenomenon,spacial distribution of streamwise and vertical components of vorticity with specific signs in the near wake,is analyzed based on two models of streamwise and vertical vortices in explaining physical reasons of top and bottom shear layers wavily varied across the *** these two models and above two interactions are *** two sign laws are summarized:the first sign law for streamwise and vertical components of vorticity is positive in the upper shear layer,but negative in the lower shear layer,while the second sign law for three vorticity components is always negative in the wake.

关键词： Vortex-shedding pattern flow control Vortex dynamics Conic disturbance Perforation Sign law

Effect of perforation on flow past a conic cylinder at Re=100:vortex-shedding pattern and force history

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Acta Mechanica Sinica 2018年第2期34卷 238-256页

作者： l.M.lin x.f.Zhong Y.x.Wu Key laboratory for Mechanics in fluid Solid Coupling Systems Institute of Mechanics Chinese Academy of Sciences

The flow past a circular-section cylinder with a conic shroud perforated with four holes at the peak was simulated numerically at Re = 100, considering two factors, *** angle of attack and the diameter of the holes. The effects of the perforated conic shroud on the vortex shedding pattern in the near wake was mainly investigated, as well as the time history of the drag and lift forces. In the investigated parameter space, three flow regimes were generally identified, corresponding to weak, moderate, and strong disturbance *** regime I, the wake can mainly be described by alternately shedding Kármán or Kármán-like vortices. In regime II, the spanwise vortices are obviously disturbed along the span due to the appearance of additional vorticity components and their interactions with the spanwise vortices, but still shed in synchronization along the spanwise direction. In regime III,the typical Kármán vortices partially or totally disappear,and some new vortex shedding patterns appear, such as-type, obliquely shedding, and crossed spanwise vortices with opposite sign. Corresponding to these complex vortex shedding patterns in the near wake, the fluid forces no longer oscillate regularly at a single vortex shedding frequency, but rather with a lower modulation frequency and multiple amplitudes. An overview of these flow regimes is presented.

关键词： Vortex shedding pattern fluid forces flow control Conical shroud Perforation

Accelerating bainite transformation by concurrent pearlite formation in a medium Mn steel:Experiments and modelling

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Journal of Materials Science & Technology 2024年第9期176卷 211-223页

作者： l.K.Huang f.liu M.x.Huang Department of Mechanical Engineering The University of Hong KongPokfulam RoadHong KongChina State Key laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’anShaanxi710072China

Bainite transformation has yet to be utilized and even thoroughly studied in medium Mn ***,we investigate the isothermal bainite transformation in a 10Mn steel at 450°C experimentally and theoretically,focusing on the effect of dislocations introduced by warm *** show that the bainite transformation in the studied medium Mn steel exhibits extremely sluggish kinetics(on a time scale of days),concurrent with the pearlite *** introduced dislocations can significantly accelerate bainite transformation kinetics while also facilitating the pearlite *** is likely the first report on the simultaneous occurrence of these two solid-state reactions in medium Mn *** respect to the roles of dislocations in the acceleration of bainite transformation observed in this work,we propose a new‘carbon depletion mechanism’,in which dislocations-stimulated pearlite formation makes a twofold contribution:facilitating the formation of bainitic ferrite sub-units to further enhance the autocatalytic effect and preventing the carbon enrichment in the remaining *** this basis,a physical model is developed to quantitatively understand the bainite transformation kinetics considering the effect of concurrent pearlite formation,revealing good agreements between model descriptions and experiment *** findings,herein,offer fundamental insights into the bainite transformation in medium Mn steels and uncover a previously unidentified role played by introduced dislocations in influencing the kinetics of bainite formation,which may guide its future application in manipulating microstructure for the development of advanced high-strength steels.

关键词： Medium Mn steels Bainite Thermodynamics Kinetics Phase transformation

Spalling characteristics of high-temperature treated granitic rock at different strain rates

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第4期16卷 1280-1288页

作者： l.f.fan Q.H.Yang x.l.Du The Key laboratory of Urban Security and Disaster Engineering of Ministry of Education Beijing University of TechnologyBeijing100124China

The dynamic spalling characteristics of rock are important for stability analysis in rock *** paper presented an experimental investigation on the dynamic spalling characteristics of granite with different temperatures and strain rates.A series of dynamic spalling tests with different impact velocities were conducted on thermally treated granite at different *** dynamic spalling strengths of granite with different temperatures and strain rates were determined.A model was proposed to correlate the dynamic spalling strength of granite,high temperature and strain *** results show that the spalling strength of granite decreases with increasing ***,the spalling strength of granite with a higher strain rate is larger than that with a lower strain *** proposed model can describe the relationship among dynamic spalling strength of granite,high temperature and strain rate.

关键词： Dynamic spalling characteristics High temperature Strain rate Dynamic loading Granite

Mechanism of wavy vortex and sign laws in flow past a bluff body:vortex-induced vortex

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Acta Mechanica Sinica 2019年第1期35卷 1-14,I0001页

作者： l.M.lin S.Y.Shi x.f.Zhong Y.x.Wu Key laboratory for Mechanics in fluid Solid Coupling Systems Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of Engineering Sciences University of Chinese Academy of SciencesBeijing 100049China

As reported in a previous work by lin et al.(Acta Meeh Sin, 2018. https://***/10.1007/s 10409-018-0758-z), an interesting phenomenon was discovered based on the analysis of wavy vortex and vorticity distribution in the shear layers and near wake of a peak-perforated conic shroud, and two sign laws were summarized. In the present paper, the theory of a vortex-induced vortex is introduced to explore mechanisms in a wavy vortex and applicable sign laws for uniform and incompressible flow past a fixed bluff body. Based on the analysis of the nearest-wall How, two vortex-induced models for streamwise and vertical vortex pairs, respectively, are proposed under two boundary cases, denoting the induced vorticity introduced or distributed on and near the walls. As a result, the first sign law, for only streamwise and vertical components of vorticity, and the second sign law, for three components of vorticity, are obtained under their own particular conditions. The first sign law reveals the intrinsic physical relationship between streamwise and vertical vorticities, independent of the distribution of spanwise vortices in the whole flow field. It is also confirmed that the spanwise vortices, as well as the shear layers and wake width, distributed wavily across the span, are attributed to the introduced streamwise or vertical vortices. The two sign laws for vorticity are independent of the disturbed spanwise wavelength and the Reynolds number. Through the analysis of flow past the conic shroud, the two sign laws are successfully used to summarize typical spacial distributions of vorticity in three flow regions: on and near the front cylinder surfaces, the separated shear layers and the near wake.

关键词： Wavy vortex Sign law Vortex-induced vortex Wake Bluff body

Morphology Control and Optical Absorption Properties of Ag Nanoparticles by Ion Implantation

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Journal of Materials Science & Technology 2009年第5期25卷 669-672页

作者： G.x. Cai f. Ren x.H. xiao l.x. fan x.D. Zhou C.Z. Jiang Key laboratory of Acoustic and Photonie Materials and Devices of Ministry of Education Wuhan University Wuhan 430072 China

Ion implantation is a powerful method for fabricating nanoparticles in dielectric. for the actual application of nanoparticle composites, a careful control of nanoparticles has to be achieved. In this letter, the size, distribution and morphology of Ag nanoparticles are controlled by controlling the ion current density, ion implantation sequence and ion irradiation dose. Single layer Ag nanoparticles are formed by Ag^＋ ion implantation at current density of 2.5 μ^A/cm2. By Ag and Cu ions sequential implantation, the size of single layer Ag nanoparticles increases. While, by Cu and Ag ions sequential implantation, uniform Ag nanoparticles with wide distribution are formed. The morphology of Ag nanoparticles changes to hollow and sandwiched nanoparticles by Cu^＋ ion irradiation to doses of 3×10^16 and 5×10^16 ions/cm^2. The optical absorption properties of Ag nanoparticles are also tailored by these ways.

关键词： Nanoparticles Ion implantation Transmission electron microscopy

xPS INVESTIGATION Of NITROGEN IONS IMPlANTED INTO AlUMINUM AllOY BY PlASMA BASED ION IMPlANTATION

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Acta Metallurgica Sinica(English letters) 1999年第5期12卷 771-776页

作者： Zhan, Z.J. Ma, x.x. xia, l.f. Sun, Y. Harbin Inst of Technology Harbin China

Aluminum alloy 2024 has been implanted with nitrogen ions at various doses by plasma based ion implantation. The introduction of energetic ions causes structural change within the near surface region of the solid. The samples have been characterized by x-ray Photoelectron Spectroscopy at various depths. The chemical states of Al and N were identified by deconvolution of the recorded xPS spectra. After plasma based ion implanted nitrogen into aluminum, not only the AlN precipitates but also super saturated solution of nitrogen forms. The presence of aluminum in different chemical states is corresponding to Al, AlN and Al2O3. The majority of nitrogen is in the form of the supersaturated solution. With the increase of nitrogen dose, the amount of AlN precipitates increases.

关键词： Aluminum compounds Ion implantation Nitrides Nitrogen Plasma devices Wear of materials

Measurements of γ/γ' lattice Misfit and γ' Volume fraction for a Ru-containing Nickel-based Single Crystal Superalloy

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Journal of Materials Science & Technology 2011年第10期27卷 899-905页

作者： x.P. Tan J.l. liu x P Song T. Jin x.f. Sun Z.Q. Hu Superalloy Division Institute of Metal Research Chinese Academy of Sciences- Shenyang 110016 China Analysis and Testing Division Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China

A conventional x-ray diffractometer has been used to determine the -y/y＇ lattice misfit and γ＇ volume fraction for a Ru-containing nickel-based single crystal superalloy at room temperature. The rocking curve was used to characterize the distribution of subgrains. The diffraction peaks obtained by w-20 scan were used to determine the γ/γ＇ lattice misfit and γ＇ volume fraction. A three peaks fitting model was proposed. The peak fitting results are in good agreement with the model. The x-ray diffraction results indicate that the nickel-based single crystal superalloy was not a perfect monocrystalline material, which is comprised of many subgrains; and each subgrain also consists of large numbers of mosaic structures. In addition, two anomalous reflection phenomena were found during the experiment and discussed with respect to their occurrence and impact on the measurement. The experimental results show that the γ/γ＇ lattice misfit and ~/r volume fraction will be various at the different regions of its dendritic microstructure. The average γ/γ＇ lattice misfit and γ＇ volume fraction of the experimental alloy are approximately-0.2% and 70%, respectively. furthermore, the γ＇ volume fraction calculated by atom microprobe （AP） data is also basically consistent with the experimental results.

关键词： Nickel-based superalloy Microstructure x-ray diffraction lattice misfit y' volume fraction

Phase Selection in Solidi?cation of Undercooled Co–B Alloys

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Journal of Materials Science & Technology 2017年第4期33卷 352-358页

作者： x.x.Wei W.xu J.l.Kang M.ferry J.f.li State Key laboratory of Metal Matrix Composites School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai 200240.China Australian Research Council Centre of Excellence for Design in light Metals School of Materials Science and EngineeringThe University of New South WalesSydneyNSW 2052Australia

A series Co-（18.5–20.7） at.% B melts encompassing the eutectic composition（Co81.5B18.5） were solidified at different degrees of undercooling. It is found that the metastable Co23B6 phase solidifies as a substitute for the stable Co3 B phase in the alloy melts undercooled above a critical undercooling value of -60 *** Co23B6 and α-Co phases make up a metastable eutectic. The corresponding eutectic composition and temperature are Co80.4B19.6 and 1343 K, respectively. On exposure of the metastable Co23B6 phase at a given temperature above 1208 K, it does not decompose even after several hours. But it transforms by a eutectoid reaction to α-Co ＋ Co3 B at lower temperature.

关键词： Undercooling Rapid solidi?cation Metastable phase diagram Structure evolution