IMECH-IR中国科学院力学研究所http://dspace.imech.ac.cn:802020-12-01T11:12:19Z2020-12-01T11:12:19ZOn the self-constraint mechanism of the cross-stream secondary flow in a streamwise-rotating channel杨子轩Deng BQWang BCShen Lhttp://dspace.imech.ac.cn:80/handle/311007/853972020-11-30T08:11:02Z2020-11-30T01:07:22ZTitle: On the self-constraint mechanism of the cross-stream secondary flow in a streamwise-rotating channel
Authors: 杨子轩; Deng BQ; Wang BC; Shen L
Description: The mechanism underlying the magnitude-reverse phenomenon of the mean spanwise velocity with respect to an increasing rotation number in a streamwise-rotating channel flow is investigated through a budget balance analysis of Reynolds shear stress u2 ' u3 '. It is found that u2 ' u3 ' imposes a negative feedback to itself through the production term, which prevents its magnitude from increasing monotonically with an increasing rotation number. This behavior of u2 ' u3 ' further leads to the magnitude reverse in the spanwise wall shear stress and mean spanwise velocity in the near-wall region.2020-11-30T01:07:22ZAssessment of Parshall flumes for discharge measurement of open-channel flows: A comparative numerical and field case studyKhosronejad AHerb WSotiropoulos FKang S杨晓雷http://dspace.imech.ac.cn:80/handle/311007/853942020-11-30T08:11:04Z2020-11-30T01:07:20ZTitle: Assessment of Parshall flumes for discharge measurement of open-channel flows: A comparative numerical and field case study
Authors: Khosronejad A; Herb W; Sotiropoulos F; Kang S; 杨晓雷
Description: This paper presents a series of numerical and field studies to examine the accuracy of two field-scale Parshall flumes, which are employed to measure the flow rate of a wastewater system in the city of Minneapolis, Minnesota. The numerical studies were carried out using the large-eddy simulation (LES) and level-set methods to compute the turbulent flow of sewers under two-phase flow (wastewater and air) conditions. Flow rate measurements in the field were conducted using the dye dilution approach and an in-site flow measuring tool. Using the combination of field measurements and numerical simulations, this research aims at quantifying (i) the margin of error of the filed-scale Parshall flumes and (ii) the water surface fluctuations within the Parshall flumes. The LES turbulent model, coupled with the level-set method, allowed for resolution of instantaneous water surface variations and uncertainty quantification of the flow rate measurements.2020-11-30T01:07:20ZCoaxial Thermocouples for Heat Transfer Measurements in Long-Duration High Enthalpy Flows张仕忠汪球李进平张晓源陈宏http://dspace.imech.ac.cn:80/handle/311007/853912020-11-30T08:11:04Z2020-11-30T01:07:19ZTitle: Coaxial Thermocouples for Heat Transfer Measurements in Long-Duration High Enthalpy Flows
Authors: 张仕忠; 汪球; 李进平; 张晓源; 陈宏
Description: Coaxial thermocouples have the advantages of fast response and good durability. They are widely used for heat transfer measurements in transient facilities, and researchers have also considered their use for long-duration heat transfer measurements. However, the model thickness, transverse heat transfer, and changes in the physical parameters of the materials with increasing temperature influence the accuracy of heat transfer measurements. A numerical analysis of coaxial thermocouples is conducted to determine the above influences on the measurement deviation. The minimum deviation is obtained if the thermal effusivity of chromel that changes with the surface temperature is used to derive the heat flux from the surface temperature. The deviation of the heat flux is less than 5.5% when the Fourier number is smaller than 0.255 and 10% when the Fourier number is smaller than 0.520. The results provide guidance for the design of test models and coaxial thermocouples in long-duration heat transfer measurements. The numerical calculation results are verified by a laser radiation heating experiment, and heat transfer measurements using coaxial thermocouples in an arc tunnel with a test time of several seconds are performed.2020-11-30T01:07:19ZOn the flow characteristics in different carotid arteries陈与杨晓雷Iskander AJWang Phttp://dspace.imech.ac.cn:80/handle/311007/853882020-11-30T08:11:05Z2020-11-30T01:07:18ZTitle: On the flow characteristics in different carotid arteries
Authors: 陈与; 杨晓雷; Iskander AJ; Wang P
Description: Hemodynamics plays an important role in the cause of atherosclerotic disease. In this work, we simulated the flow fields in six human carotids using the sharp-interface immersed boundary method. We compare the axial velocity, the secondary flow, the vortex structures, the area with reversed flows, and the standard deviation of velocity fluctuations for different carotids. The computed results show similarities among different carotids for the overall pattern of different flow characteristics. More importantly, differences are observed in terms of the details of the area of the reversed flow region, the size and shape of the region dominated by reversed flows, and the length of time with reversed flow or dominated by secondary flows, which are strongly correlated with the formation of plaques. Further analysis shows that patient-specific features of the carotid geometry, e.g., the flare and proximal curvature of the carotid, have significant effects on these flow characteristics. This suggests that a patient-specific program is needed for the prevention and treatment of atherosclerosis.2020-11-30T01:07:18ZStrain rate dependent shear localization and deformation mechanisms in the CrMnFeCoNi high-entropy alloy with various microstructures杨正凌杨沐鑫马彦周玲玲程文强袁福平武晓雷http://dspace.imech.ac.cn:80/handle/311007/853852020-11-30T08:11:06Z2020-11-30T01:07:17ZTitle: Strain rate dependent shear localization and deformation mechanisms in the CrMnFeCoNi high-entropy alloy with various microstructures
Authors: 杨正凌; 杨沐鑫; 马彦; 周玲玲; 程文强; 袁福平; 武晓雷
Description: CrMnFeCoNi high-entropy alloys (HEA) with various microstructures have been produced using cold rolling followed by critical annealing at various temperatures. Shear deformation behaviors of this HEA with various microstructures at a wide range of strain rates (2 x 10(-3)-5 x 10(4) s(-1)) have been characterized using hat-shaped specimens. Strain hardening exponent and strain rate sensitivity have been obtained for various microstructures. No shear localization was observed up to shear strain of 8 for all microstructures under lower strain rates (2 x 10(-3)-1 x 10(1) s(-1)), while stress drop and shear localization were found to occur at various critical shear strains for various microstructures under dynamic shear loading (5 x 10(4) s(-1)). A new formula, considering competition of strain hardening and strain rate hardening against thermal softening, was proposed to estimate the critical shear strains under dynamic shear loading and the predicted results were found to be in a fairly good agreement with the experimental data. Based on micro-hardness testing, the strain hardening due to the microstructure evolution was found be much stronger under dynamic shear loading than that under quasi-static loading at the same interrupted shear strain, which can be attributed to the more efficient grain refinement and the triggered hierarchical deformation nanotwins under dynamic shear deformation.2020-11-30T01:07:17ZShape evolution and scaling analysis of soluble cylinders in dissolutive flow苗青袁泉子赵亚溥http://dspace.imech.ac.cn:80/handle/311007/853822020-11-30T08:11:07Z2020-11-30T01:07:15ZTitle: Shape evolution and scaling analysis of soluble cylinders in dissolutive flow
Authors: 苗青; 袁泉子; 赵亚溥
Description: The evolution of solid shapes in dissolutive flows is studied using molecular dynamics simulations. The final self-similar structures of the solid are distinct under the convection- and diffusion-dominated conditions. Introducing a dimensionless number, Ds, allows characterizing the relative influence of convection and diffusion on the final structure. When convection dominates, the convergent shape of the solid is approximately triangular, while the solid is more likely to be sculptured into a cylinder when diffusion dominates. There is a critical value of Ds that controls the transition between convection- and diffusion-dominated cases. However, the convergent shapes are insensitive to their initial states due to the solid assembly at the nanoscale. Furthermore, we discuss the influences of solid dissolution and assembly on the liquid density along different directions and provide fitting curves for the theoretical density distribution as explained from the Smoluchowski equation. Finally, the scaling laws are constructed to quantify the solid evolution, which can analytically forecast the shape evolution under different dominant factors. We believe that these findings provide theoretical support for structure optimization and industrial applications.2020-11-30T01:07:15ZAnalysis of the critical heat flux of subcooled flow boiling in microgravityLiu BYuan BZhou J赵建福Di Marco PZhang YHWei JJYang Yhttp://dspace.imech.ac.cn:80/handle/311007/853792020-11-30T08:11:07Z2020-11-30T01:07:14ZTitle: Analysis of the critical heat flux of subcooled flow boiling in microgravity
Authors: Liu B; Yuan B; Zhou J; 赵建福; Di Marco P; Zhang YH; Wei JJ; Yang Y
Description: There is a significant decrease in flow boiling CHF when the inertial force of the fluid is not large enough in microgravity, but this tendency decreases with the increase of the inertial force. In the present study, the critical heat flux (CHF) of subcooled flow boiling at different gravity levels on smooth silicon surfaces was investigated. The working fluid is FC-72, with the subcooling of 15 K. The flow boiling heat transfer characteristics, including the CHF, wall temperatures and bubble behavior were studied. The effects of the heater length, channel height and flow velocity on the CHF were studied. It was found that the CHF increases with the increase of the channel height and flow velocity, but decreases with the increase of the heater length. A similar tendency was found for the ratio of the CHF in microgravity to that in normal gravity (q(CHF-mu g)/q(CHF-1g)). The relation of the flow velocity, heater length, channel geometrical parameters, and q(CHF)(-mu g)/q(CHF-1g) was studied by the dimensionless analysis. Finally, a correlation for the prediction of q(CHF-mu g)/q(CHF-1g) was developed based on the dimensionless analysis and the prediction results agree quite well with the experimental data within +/- 10%.2020-11-30T01:07:14ZEffect of Process Parameters on Defects, Melt Pool Shape, Microstructure, and Tensile Behavior of 316L Stainless Steel Produced by Selective Laser Melting蒋华臻李正阳Feng TWu PY陈启生Feng YLChen LF侯静宇Xu HJhttp://dspace.imech.ac.cn:80/handle/311007/853762020-11-30T08:11:08Z2020-11-30T01:05:00ZTitle: Effect of Process Parameters on Defects, Melt Pool Shape, Microstructure, and Tensile Behavior of 316L Stainless Steel Produced by Selective Laser Melting
Authors: 蒋华臻; 李正阳; Feng T; Wu PY; 陈启生; Feng YL; Chen LF; 侯静宇; Xu HJ
Description: Previous studies have revealed that laser power and energy density are significant factors affecting the quality of parts manufactured by selective laser melting (SLM). The normalized equivalent densityE(0)* and dimensionless laser powerq*, which can be regarded as a progress on the understanding of the corresponding dimensional quantities, are adopted in this study to examine the defects, melt pool shape, and primary dendrite spacing of the SLM-manufactured 316L stainless steel, because it reflects the combined effect of process parameters and material features. It is found that the number of large defects decreases with increasingE(0)* due to enough heat input during the SLM process, but it will show an increasing trend when excessive heat input (i.e., utilizing a highE(0)*) is imported into the powder bed. Theq* plays an important role in controlling maximum temperature rising in the SLM process, and in turn, it affects the number of large defects. A largeq* value results in a low value of absolute frequency of large defects, whereas a maximum value of absolute frequency of large defects is achieved at a lowq* even ifE(0)* is very high. The density of the built parts is greater at a higherq* whenE(0)* remains constant. Increasing the melt pool depth at relatively low value ofE(0)* enhances the relative density of the parts. A narrow, deep melt pool can be easily generated at a highq* whenE(0)* is sufficiently high, but it may increase melt pool instability and cause keyhole defects. It is revealed that a lowE(0)* can lead to a high cooling rate, which results in a refined primary dendrite spacing. Relatively lowE(0)* is emphasized in selecting the process parameters for the tensile test sample fabrication. It shows that excellent tensile properties, namely ultimate tensile strength, yield strength, and elongation to failure of 773 MPa, 584 MPa, and 46%, respectively, can be achieved at a relatively lowE(0)* without heat treatment.2020-11-30T01:05:00ZMicrotubule-Mediated Wall Anisotropy Contributes to Leaf Blade FlatteningZhao FDu FOliveri H周吕文Ali OChen WQ冯世亮Wang QQ吕守芹龙勉Schneider RSampathkumar AGodin CTraas JJiao YLhttp://dspace.imech.ac.cn:80/handle/311007/853732020-11-30T08:11:10Z2020-11-30T01:04:58ZTitle: Microtubule-Mediated Wall Anisotropy Contributes to Leaf Blade Flattening
Authors: Zhao F; Du F; Oliveri H; 周吕文; Ali O; Chen WQ; 冯世亮; Wang QQ; 吕守芹; 龙勉; Schneider R; Sampathkumar A; Godin C; Traas J; Jiao YL
Description: Plant organs can adopt a wide range of shapes, resulting from highly directional cell growth and divisions. We focus here on leaves and leaf-like organs in Arabidopsis and tomato, characterized by the formation of thin, flat laminae. Combining experimental approaches with 3D mechanical modeling, we provide evidence that leaf shape depends on cortical microtubule mediated cellulose deposition along the main predicted stress orientations, in particular, along the adaxial-abaxial axis in internal cell walls. This behavior can be explained by a mechanical feedback and has the potential to sustain and even amplify a preexisting degree of flatness, which in turn depends on genes involved in the control of organ polarity and leaf margin formation.2020-11-30T01:04:58ZHeterostructured materials: superior properties from hetero-zone interactionZhu YTAmeyama KAnderson PMBeyerlein IJGao HJKim HSLavernia EMathaudhu SMughrabi HRitchie ROTsuji NZhang XY武晓雷http://dspace.imech.ac.cn:80/handle/311007/853702020-11-30T08:11:11Z2020-11-30T01:04:56ZTitle: Heterostructured materials: superior properties from hetero-zone interaction
Authors: Zhu YT; Ameyama K; Anderson PM; Beyerlein IJ; Gao HJ; Kim HS; Lavernia E; Mathaudhu S; Mughrabi H; Ritchie RO; Tsuji N; Zhang XY; 武晓雷
Description: Heterostructured materials are an emerging class of materials with superior performances that are unattainable by their conventional homogeneous counterparts. They consist of heterogeneous zones with dramatic (>100%) variations in mechanical and/or physical properties. The interaction in these hetero-zones produces a synergistic effect where the integrated property exceeds the prediction by the rule-of-mixtures. The heterostructured materials field explores heterostructures to control defect distributions, long-range internal stresses, and nonlinear inter-zone interactions for unprecedented performances. This paper is aimed to provide perspectives on this novel field, describe the state-of-the-art of heterostructured materials, and identify and discuss key issues that deserve additional studies.2020-11-30T01:04:56Z