This study aims to analyze the influence of vortex motion in a reverse Stairmand cyclone separator by using LES model.The mathematical analysis indicated that the energy dissipation and the flow characteristics of inc...This study aims to analyze the influence of vortex motion in a reverse Stairmand cyclone separator by using LES model.The mathematical analysis indicated that the energy dissipation and the flow characteristics of incompressible fluid are directly related to on the vortex motion.The results of the Q criterion-based iso-vortex surface could well reflect the tendency of the vortex structure,in which the iso-vortex surface exhibited a distorted distribution rather than around the center axis.At the turning point of velocity vector,vortices were formed and developed,and the point was the center of the local vortex core.In addition,the vortex formed an irregular annular region around the wall at the bottom of vortex finder.The vortex structure near the dust hopper presented a strong distortion.Moreover,there were two rotating flow in the opposite direction within the dust hopper.These phenomena would affect the separation performance,which was significance to cyclone separator.展开更多
A new hybrid model, which is based on domain decomposition and proposed by the authors is used for calculating the flow around a circular cylinder at low and middle Keulegan-Carpenter numbers (Kc=2～18)respectively.Th...A new hybrid model, which is based on domain decomposition and proposed by the authors is used for calculating the flow around a circular cylinder at low and middle Keulegan-Carpenter numbers (Kc=2～18)respectively.The vortex motion patterns in asymmetric regime,single pair(or transverse)regime and double pair(or diagonal)regime are successfully simulated.The calculated drag and inertial force coefficients are in better agreement with experimental data than other recent computational results.展开更多
We study the vortex dynamics of the polycrystalline superconductors in the presence of both random point defects and the generated grain boundary(GB) networks with Voronoi diagram. The synergistic effect of adjacent G...We study the vortex dynamics of the polycrystalline superconductors in the presence of both random point defects and the generated grain boundary(GB) networks with Voronoi diagram. The synergistic effect of adjacent GBs on restricting the vortex motion in intragranular region is proposed and the corresponding intensity factor of the synergistic effect which characterizes the strength of the synergistic restriction of adjacent grain boundaries is also determined in the present work.The interconnected GBs offer easy-flow channels for vortices in addition to pinning effects on the vortices. The combined channels and the vortex flow patterns in the superconducting film are analyzed in detail from molecular dynamics simulations. Furthermore, it is discovered that the critical current increases with the decrease of magnetic field intensity,temperature, and the average grain size. The large number of vortices results in the enhanced repulsive interaction forcing the vortices to move out from the GBs. The thermal depinning from GBs leads to the lower Lorentz force range. The increase of the grain size causes the number of GBs to decrease. In summary, these effects leads the critical current to become a decreasing function of magnetic field, temperature, and grain size.展开更多
Grain boundaries(GBs),as extremely anisotropic pinning defects,have a strong impact on vortex motion in type-Ⅱsuperconductors,and further on the macro level dominates the superconductivity for example the critical cu...Grain boundaries(GBs),as extremely anisotropic pinning defects,have a strong impact on vortex motion in type-Ⅱsuperconductors,and further on the macro level dominates the superconductivity for example the critical current density.Many previous studies indicated that mostly GB plays the role of a strong barrier for vortex motion,while an easy-flow channel just under some certain conditions.In order to thoroughly make clear of the questions of what is exactly the role of GB on vortex motion and how it works,in this article we developed a large scale molecular dynamic model and revealed the action of GB on vortex motion in type-Ⅱsuperconductors.The most significant finding is that the role of GB on vortex motion can be changeable from a barrier to an easy-flow channel,and which is intrinsically determined by the competition effect correlated with its action on vortex between in the GB and no-GB regions.Such the competition effect essentially depends on the attributes of both the GB(described by the GB strength and angleθ)and no-GB pining regions(by the relative disorder strengthα_(p)/α_(v)).Specifically,for a YBa_(2)Cu_(3)O_(7-x)(YBCO)sample,to obtain a clear knowledge of vortex motion in GB region,we visualized the three typical trajectories of vortices during the three vortex movement stages.Further,in order to understand how GB results in the macro current-carrying property,corresponding to the current-voltage relation of the YBCO conductor,we obtained the average velocity v_(y) of vortices varying with their driving force,which is nearly identical with the previous observations.展开更多
The dynamic stall process in three-dimensional （3D） cases on a rectangular wing undergoing a constant rate ramp-up motion is introduced to provide a qualitative analysis about the onset and development of the stall ...The dynamic stall process in three-dimensional （3D） cases on a rectangular wing undergoing a constant rate ramp-up motion is introduced to provide a qualitative analysis about the onset and development of the stall phenomenon. Based on the enhanced understanding of the mechanism of dynamic stalls, a 3D dynamic stall model is constructed with the emphasis of the onset, the growth, and the convection of the dynamic stall vortex on the 3D wing surface. The results show that this engineering dynamic stall model can simulate the 3D unsteady aerodynamic performance appropriately.展开更多
The sloshing problem for a spherical tank partially filled with liquid is analysed in this paper The study is based on the goveming equations of fluid dynamics and the Euler's equations of systems with the influen...The sloshing problem for a spherical tank partially filled with liquid is analysed in this paper The study is based on the goveming equations of fluid dynamics and the Euler's equations of systems with the influences of tank off centering,fluid vortices and the Coriolis'acceleration on the motion states of the systems taken into consideration.In the study,we adopt the concept of uniform vortex motion of fluid gen- eralized by Pfeiffer and apply the boundary element method(BEM)to the calculation of the natural frequence and the velocity field of the liquid sloshing.The motion charateristics of the flow-solid spinning system is then analysed.展开更多
Vortex motion in superconductors of high-To superconducting maglev system is studied by a computational simulation. The vortex system is treated in a similar fashion, as a system where defects are arranged in periodic...Vortex motion in superconductors of high-To superconducting maglev system is studied by a computational simulation. The vortex system is treated in a similar fashion, as a system where defects are arranged in periodic arrays and driven by an alternating current （AC） field. Computational simulation reveals that due to the high nonlinearity of the vortex-defect interaction, the system shows typical chaotic characters. Effects of the vortex-vortex coupling, the driving frequency, and the vortex viscosity on the vortex motion have been studied to reveal the interaction between the spatial and temporal chaos. It is found that the mean-field approach is a good approximation to describe the vortex motion in one dimensional vortex system under an AC driving field. The vortex motion under the damping mode is a kind of self-organized motion. Lastly, the spatial chaos can dominate the chaotic behavior of the system.展开更多
The structure of the concave-convex plates has proven to be crucial in optimizing the internal flow characteristics of the electrolyzer for hydrogen production.This paper investigates the impact of the gradual expansi...The structure of the concave-convex plates has proven to be crucial in optimizing the internal flow characteristics of the electrolyzer for hydrogen production.This paper investigates the impact of the gradual expansion angle of the inlet channel on the internal flow field of alkaline electrolyzers.The flow distribution characteristics of concave-convex plates with different inlet angle structures in the electrolytic cell is discussed.Besides,the system with internal heat source is studied.The results indicate that a moderate gradual expansion angle is beneficial for enhancing fluid uniformity.However,an excessively large gradual expansion angle may lead to adverse reflux phenomena,reducing the overall performance of the electrolytic cell.展开更多
Vortex shedding from a circular cylinder subjected to fortal oscillations at arbitrary angles(as shown in Fis. 1 for 0°<β<90°) with respect to the free stream is numerically investigated using the Nav...Vortex shedding from a circular cylinder subjected to fortal oscillations at arbitrary angles(as shown in Fis. 1 for 0°<β<90°) with respect to the free stream is numerically investigated using the Navier-Stokes equations. The emphasis of this study is put on revealing the complicated vortex structures and their evolution in the near wake. In the present study, a number of possible vortex modes are also numerically simulated, and a variety of physical phenomena are duplicated and even renewed numerically. A parameter map indicating the classification of preferred vortex modes is firstly given in the frequency-amplitude plane.展开更多
In this paper the VOF (Volume of Fluid) method is used to numerically study the interaction of double viscous vortex dipoles with free surface in a two dimensional incompressible flow field. From the results of this...In this paper the VOF (Volume of Fluid) method is used to numerically study the interaction of double viscous vortex dipoles with free surface in a two dimensional incompressible flow field. From the results of this research, it is found that the general consequence of the interaction is qualitatively equivalent to the problem of a single vortex dipole interacts with a free surface.展开更多
In this paper,numerical simulation is conducted via our in-house solver,vim-FOAM-SJTU,developed on open-source software,OpenFOAM.Flow around static rigid cylinders and elastically mounted rigid cylinder constrained to...In this paper,numerical simulation is conducted via our in-house solver,vim-FOAM-SJTU,developed on open-source software,OpenFOAM.Flow around static rigid cylinders and elastically mounted rigid cylinder constrained to free stream with free end are numerically investigated.Some significant conclusions are made by analyzing the different results between cases with and without free end.The turbulence model is implemented with a shear stress transport-based(SST-based)improved delayed detached eddy simulation(IDDES)approach in the vim-FOAM-SJTU.Firstly,The paper starts with the application of the vim-FOAM-SJTU solver to flow past fixed cylinder with free end at Reynolds number 43000.The numerical results are compared with experimental data.Comparison are satisfactory which implies the validity and accuracy of the current computational fluid dynamics(CFD)solver.The flow visualization in the vicinity of free-end is discussed.Subsequently,the solver is utilized to simulate the free end effect associated with the VIM of a cylinder submerged in current.The motion responses under different inflow velocities are studied.The relationship between transverse motion frequency,in-line motion frequency is discussed.Lastly,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 cylinder.The responses of circular cylinder with or without free end are compared.展开更多
MgB_(2)is a perspective superconductor for many power applications.How this potential refers also to microwave or radiofrequency applications is still to be determined.Although its ultimate surface resistance in zero ...MgB_(2)is a perspective superconductor for many power applications.How this potential refers also to microwave or radiofrequency applications is still to be determined.Although its ultimate surface resistance in zero field is not competitive with conventional metallic superconductors,its strong pinning properties can favor RF applications in a dc magnetic field.Nonetheless,the RF response in the vortex state has been relatively less studied,as well as the effect of artificial pinning centers on the microwave surface resistance in the mixed state.In this paper we study the surface resistance of spark-plasma-sintered MgB_(2),with and without Te and cubic-BN(cBN)addition,in a dc magnetic field up to 1.2 T.We summarize previous results on pure MgB_(2),and we present new data on Te-and cBN-added MgB_(2).We use a two-tone dielectric-loaded resonator to measure the field-dependent surface resistance at 16.5 and 26.7 GHz in the temperature range from 10 K to T_(c).By exploiting the simultaneous measurements at two frequencies,we extract the flux-flow resistivity,the pinning constant k_(p)and the depinning frequency f_(p).The two-band nature of MgB_(2)affects the field dependence of the flux-flow resistivity.The microscopic superconducting state is not affected by the addition of artificial pinning centers,indicating that Te and cBN do not affect interband or intraband scattering.Pinning shows a measurable trend towards an increase in the Te-and cBN-added samples at higher temperatures and fields.We finally compare the results to those obtained in bulk Nb3 Sn,also in view of possible in-field RF applications such as microwave cavity-based haloscopes.展开更多
基金support from and the Scientific Research Staring Foundation of Hainan University,No.KYQD(ZR)20042Young Talents’Science and Technology Innovation Project of Hainan Association for Science and Technology,No.QCXM202027supported by Hainan Provincial Natural Science Foundation of China,No.520QN228
文摘This study aims to analyze the influence of vortex motion in a reverse Stairmand cyclone separator by using LES model.The mathematical analysis indicated that the energy dissipation and the flow characteristics of incompressible fluid are directly related to on the vortex motion.The results of the Q criterion-based iso-vortex surface could well reflect the tendency of the vortex structure,in which the iso-vortex surface exhibited a distorted distribution rather than around the center axis.At the turning point of velocity vector,vortices were formed and developed,and the point was the center of the local vortex core.In addition,the vortex formed an irregular annular region around the wall at the bottom of vortex finder.The vortex structure near the dust hopper presented a strong distortion.Moreover,there were two rotating flow in the opposite direction within the dust hopper.These phenomena would affect the separation performance,which was significance to cyclone separator.
基金The project supported by the National Natural Science Foundations of China the LNM,Institute of Mechanics,Academia Sinica
文摘A new hybrid model, which is based on domain decomposition and proposed by the authors is used for calculating the flow around a circular cylinder at low and middle Keulegan-Carpenter numbers (Kc=2～18)respectively.The vortex motion patterns in asymmetric regime,single pair(or transverse)regime and double pair(or diagonal)regime are successfully simulated.The calculated drag and inertial force coefficients are in better agreement with experimental data than other recent computational results.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 12232005 and 12072101)。
文摘We study the vortex dynamics of the polycrystalline superconductors in the presence of both random point defects and the generated grain boundary(GB) networks with Voronoi diagram. The synergistic effect of adjacent GBs on restricting the vortex motion in intragranular region is proposed and the corresponding intensity factor of the synergistic effect which characterizes the strength of the synergistic restriction of adjacent grain boundaries is also determined in the present work.The interconnected GBs offer easy-flow channels for vortices in addition to pinning effects on the vortices. The combined channels and the vortex flow patterns in the superconducting film are analyzed in detail from molecular dynamics simulations. Furthermore, it is discovered that the critical current increases with the decrease of magnetic field intensity,temperature, and the average grain size. The large number of vortices results in the enhanced repulsive interaction forcing the vortices to move out from the GBs. The thermal depinning from GBs leads to the lower Lorentz force range. The increase of the grain size causes the number of GBs to decrease. In summary, these effects leads the critical current to become a decreasing function of magnetic field, temperature, and grain size.
基金Project supported financially by the National Natural Science Foundation of China(Grant No.12072101)the Fundamental Research Funds for the Central Universities,China(Grant No.2018B48714).
文摘Grain boundaries(GBs),as extremely anisotropic pinning defects,have a strong impact on vortex motion in type-Ⅱsuperconductors,and further on the macro level dominates the superconductivity for example the critical current density.Many previous studies indicated that mostly GB plays the role of a strong barrier for vortex motion,while an easy-flow channel just under some certain conditions.In order to thoroughly make clear of the questions of what is exactly the role of GB on vortex motion and how it works,in this article we developed a large scale molecular dynamic model and revealed the action of GB on vortex motion in type-Ⅱsuperconductors.The most significant finding is that the role of GB on vortex motion can be changeable from a barrier to an easy-flow channel,and which is intrinsically determined by the competition effect correlated with its action on vortex between in the GB and no-GB regions.Such the competition effect essentially depends on the attributes of both the GB(described by the GB strength and angleθ)and no-GB pining regions(by the relative disorder strengthα_(p)/α_(v)).Specifically,for a YBa_(2)Cu_(3)O_(7-x)(YBCO)sample,to obtain a clear knowledge of vortex motion in GB region,we visualized the three typical trajectories of vortices during the three vortex movement stages.Further,in order to understand how GB results in the macro current-carrying property,corresponding to the current-voltage relation of the YBCO conductor,we obtained the average velocity v_(y) of vortices varying with their driving force,which is nearly identical with the previous observations.
基金supported by the National Basic Research Program of China (973 Program)(No. 2007CB714600)
文摘The dynamic stall process in three-dimensional （3D） cases on a rectangular wing undergoing a constant rate ramp-up motion is introduced to provide a qualitative analysis about the onset and development of the stall phenomenon. Based on the enhanced understanding of the mechanism of dynamic stalls, a 3D dynamic stall model is constructed with the emphasis of the onset, the growth, and the convection of the dynamic stall vortex on the 3D wing surface. The results show that this engineering dynamic stall model can simulate the 3D unsteady aerodynamic performance appropriately.
基金The projeet is supported by the National Natural Science Foundation of ChinaMinistry of Astronautics.
文摘The sloshing problem for a spherical tank partially filled with liquid is analysed in this paper The study is based on the goveming equations of fluid dynamics and the Euler's equations of systems with the influences of tank off centering,fluid vortices and the Coriolis'acceleration on the motion states of the systems taken into consideration.In the study,we adopt the concept of uniform vortex motion of fluid gen- eralized by Pfeiffer and apply the boundary element method(BEM)to the calculation of the natural frequence and the velocity field of the liquid sloshing.The motion charateristics of the flow-solid spinning system is then analysed.
文摘Vortex motion in superconductors of high-To superconducting maglev system is studied by a computational simulation. The vortex system is treated in a similar fashion, as a system where defects are arranged in periodic arrays and driven by an alternating current （AC） field. Computational simulation reveals that due to the high nonlinearity of the vortex-defect interaction, the system shows typical chaotic characters. Effects of the vortex-vortex coupling, the driving frequency, and the vortex viscosity on the vortex motion have been studied to reveal the interaction between the spatial and temporal chaos. It is found that the mean-field approach is a good approximation to describe the vortex motion in one dimensional vortex system under an AC driving field. The vortex motion under the damping mode is a kind of self-organized motion. Lastly, the spatial chaos can dominate the chaotic behavior of the system.
基金supported by Science and Technology Projects of Gansu,China(No.22ZD6GA014).
文摘The structure of the concave-convex plates has proven to be crucial in optimizing the internal flow characteristics of the electrolyzer for hydrogen production.This paper investigates the impact of the gradual expansion angle of the inlet channel on the internal flow field of alkaline electrolyzers.The flow distribution characteristics of concave-convex plates with different inlet angle structures in the electrolytic cell is discussed.Besides,the system with internal heat source is studied.The results indicate that a moderate gradual expansion angle is beneficial for enhancing fluid uniformity.However,an excessively large gradual expansion angle may lead to adverse reflux phenomena,reducing the overall performance of the electrolytic cell.
文摘Vortex shedding from a circular cylinder subjected to fortal oscillations at arbitrary angles(as shown in Fis. 1 for 0°<β<90°) with respect to the free stream is numerically investigated using the Navier-Stokes equations. The emphasis of this study is put on revealing the complicated vortex structures and their evolution in the near wake. In the present study, a number of possible vortex modes are also numerically simulated, and a variety of physical phenomena are duplicated and even renewed numerically. A parameter map indicating the classification of preferred vortex modes is firstly given in the frequency-amplitude plane.
文摘In this paper the VOF (Volume of Fluid) method is used to numerically study the interaction of double viscous vortex dipoles with free surface in a two dimensional incompressible flow field. From the results of this research, it is found that the general consequence of the interaction is qualitatively equivalent to the problem of a single vortex dipole interacts with a free surface.
基金supported by the National Natural Science Foundation of China(Grant Nos.52131102,51909160 and 51879159)the National Key Research and Development Program of China(Grant No.2019YFB1704200).
文摘In this paper,numerical simulation is conducted via our in-house solver,vim-FOAM-SJTU,developed on open-source software,OpenFOAM.Flow around static rigid cylinders and elastically mounted rigid cylinder constrained to free stream with free end are numerically investigated.Some significant conclusions are made by analyzing the different results between cases with and without free end.The turbulence model is implemented with a shear stress transport-based(SST-based)improved delayed detached eddy simulation(IDDES)approach in the vim-FOAM-SJTU.Firstly,The paper starts with the application of the vim-FOAM-SJTU solver to flow past fixed cylinder with free end at Reynolds number 43000.The numerical results are compared with experimental data.Comparison are satisfactory which implies the validity and accuracy of the current computational fluid dynamics(CFD)solver.The flow visualization in the vicinity of free-end is discussed.Subsequently,the solver is utilized to simulate the free end effect associated with the VIM of a cylinder submerged in current.The motion responses under different inflow velocities are studied.The relationship between transverse motion frequency,in-line motion frequency is discussed.Lastly,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 cylinder.The responses of circular cylinder with or without free end are compared.
基金supported by INFN-Commissione ScientificaNazionale 5 projects‘SAMARA’and‘SuperMAD’,COST Action CA19108-Hi-SCALE,and Italian National Operational Programme(PON)on Research and Innovation 2014-2020-Action IV.6.P.B.,A.C.M.A.G.acknowledge UEFISCDI Romania through Core Program PC2-PN23080202project POC 37697 no.28/01.09.2016 REBMAT.Data for the phase diagram of MgB_(2)and comparison to Nb3Sn was supported by Rome Technopole.
文摘MgB_(2)is a perspective superconductor for many power applications.How this potential refers also to microwave or radiofrequency applications is still to be determined.Although its ultimate surface resistance in zero field is not competitive with conventional metallic superconductors,its strong pinning properties can favor RF applications in a dc magnetic field.Nonetheless,the RF response in the vortex state has been relatively less studied,as well as the effect of artificial pinning centers on the microwave surface resistance in the mixed state.In this paper we study the surface resistance of spark-plasma-sintered MgB_(2),with and without Te and cubic-BN(cBN)addition,in a dc magnetic field up to 1.2 T.We summarize previous results on pure MgB_(2),and we present new data on Te-and cBN-added MgB_(2).We use a two-tone dielectric-loaded resonator to measure the field-dependent surface resistance at 16.5 and 26.7 GHz in the temperature range from 10 K to T_(c).By exploiting the simultaneous measurements at two frequencies,we extract the flux-flow resistivity,the pinning constant k_(p)and the depinning frequency f_(p).The two-band nature of MgB_(2)affects the field dependence of the flux-flow resistivity.The microscopic superconducting state is not affected by the addition of artificial pinning centers,indicating that Te and cBN do not affect interband or intraband scattering.Pinning shows a measurable trend towards an increase in the Te-and cBN-added samples at higher temperatures and fields.We finally compare the results to those obtained in bulk Nb3 Sn,also in view of possible in-field RF applications such as microwave cavity-based haloscopes.
