Vortex-shedding flow induced by the vertical oscillation of a cylinder with bottom-attached disks of different diameter ratio Dd/Dc and thickness ratio td/Dc is studied by a 3D （three-dimensional） numerical model de...Vortex-shedding flow induced by the vertical oscillation of a cylinder with bottom-attached disks of different diameter ratio Dd/Dc and thickness ratio td/Dc is studied by a 3D （three-dimensional） numerical model developed in this paper, and compared with the results obtained through 2D （two-dimensional） numerical model. The high-order upwind scheme is applied to stabilize the computation, and convergence is accelerated by the multi-grid method. Qualitative and quantitative analyses of the differences between the 2D and 3D simulation results reveal the 3D effect on the flow field characteristics and hydrodynamic coefficients of the vertically oscillating cylinder with a bottom-attached disk. The 3D effect on the fluid field is mainly reflected in the significance of three vortex-shedding patterns： ωx has a greater effect on the flow fields around the sharp edges relative to the vortices generated in the 2D simulation. In the slice along the axial orientation, the vortex effect of ωy along the radial axis is smaller than that of ωx along the circumferential direction, indicating the radial effect on the velocity more pronounced than the circumferential effect around the sharp edges of the disk. The rotational interaction ωz of the fluid in the horizontal plane during the heave motion is insignificant. Based on the 2D and 3D simulation results, the turning points that separate the increasing regimes of the added mass coefficient and damping ratio are identified. The dependence of the turning point on the diameter ratio Dd/Dc and thickness ratio td/Dc are discussed in detail.展开更多
The unsteady evolution of trailing vortex sheets behind a wing in ground effect is simulated using an unsteady discrete vortex panel method. The ground effect is included by image method. The present method is validat...The unsteady evolution of trailing vortex sheets behind a wing in ground effect is simulated using an unsteady discrete vortex panel method. The ground effect is included by image method. The present method is validated by comparing the simulated wake roll-up shapes to published numerical results. When a wing is flying in a very close proximity to the ground, the optimal wing loading is parabolic rather than elliptic. Thus, a theoretical model of wing load distributions is suggested, and unsteady vortex evolutions behind lifting lines with both elliptic and parabolic load distributions are simulated for several ground heights. For a lifting line with elliptic and parabolic loading, the ground has the effect of moving the wingtip vortices laterally outward and suppressing the development of the vortex. When the wing is in a very close proximity to the ground, the types of wing load distributions does not affect much on the overall wake shapes, but parabolic load distributions make the wingtip vortices move more laterally outward than the elliptic load distributions.展开更多
Numerical simulations are carried out for wave action on a submerged horizontal circular cylinder by means of a viscous fluid model, and it is focused on the examination of the discrepancies between the viscous fluid ...Numerical simulations are carried out for wave action on a submerged horizontal circular cylinder by means of a viscous fluid model, and it is focused on the examination of the discrepancies between the viscous fluid results and the potential flow solutions. It is found that the lift force resulted from rotational flow on the circular cylinder is always in anti-phase with the inertia force and induces the discrepancies between the results. The influence factors on the magnitude of the lift force, especially the correlation between the stagnation-point position and the wave amplitude, and the effect of the vortex shedding are investigated by further examination on the flow fields around the cylinder. The viscous numerical calculations at different wave frequencies showed that the wave frequency has also significant influence on the wave forces. Under higher frequency and larger amplitude wave action, vortex shedding from the circular cylinder will appear and influence the wave forces on the cylinder substantially.展开更多
ABSTRACT:The development of highly sensitive and rapidresponse/recovery room-temperature NH_(3) sensors is critically demanded for environmental monitoring and healthcare diagnostics,yet remains scientifically challen...ABSTRACT:The development of highly sensitive and rapidresponse/recovery room-temperature NH_(3) sensors is critically demanded for environmental monitoring and healthcare diagnostics,yet remains scientifically challenging.Inspired by the two-dimensional ordered macroporous structure of peacock feathers,two-dimensional inverse opal(2DIO)polyaniline/silver(PANI/Ag)composites were fabricated via a sacrificial templating method.By integrating the advantages of gas diffusion of highly ordered macroporous structures with the catalytic activity of Ag,significant improvements in NH_(3) sensing performance were achieved.Computational fluid dynamics(CFD)simulations demonstrated that the 2DIO structure induced vortex effects,which significantly reduced the gas velocity.Concurrently,macroporous channels(~240 nm diameter)enhanced adsorption/desorption kinetics.The fabricated 2DIO PANI/Ag sensor exhibited a remarkable response of 1153%to 100 ppm NH_(3),with ultra-fast response/recovery times of 3 s/56 s,exhibiting a 420-fold improvement in response/recovery speed compared to pure PANI(126 s/325 s).A further developed wearable detection module successfully discriminated exhalation signals between simulated chronic kidney disease(CKD)patients and healthy individuals,providing a new strategy for noninvasive medical diagnosis.In-situ Fourier transform infrared spectroscopy(in-situ FT-IR)real-time tracking of NH_(3) adsorption/desorption processes confirms a chemisorption-dominated sensing mechanism.Density functional theory(DFT)calculations showed that the charge transfer at the PANI/Ag interface enhanced the adsorption of NH_(3),which significantly enhanced the molecular affinity.This study provides a viable pathway for developing high-performance flexible NH_(3) gas sensors through an interdisciplinary approach combining structural bionics,simulation optimization,theoretical analysis,and experimental validation.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51239007 and 51179077)the Sino-UK Higher Education Research Partnership for Ph.D.Studies
文摘Vortex-shedding flow induced by the vertical oscillation of a cylinder with bottom-attached disks of different diameter ratio Dd/Dc and thickness ratio td/Dc is studied by a 3D （three-dimensional） numerical model developed in this paper, and compared with the results obtained through 2D （two-dimensional） numerical model. The high-order upwind scheme is applied to stabilize the computation, and convergence is accelerated by the multi-grid method. Qualitative and quantitative analyses of the differences between the 2D and 3D simulation results reveal the 3D effect on the flow field characteristics and hydrodynamic coefficients of the vertically oscillating cylinder with a bottom-attached disk. The 3D effect on the fluid field is mainly reflected in the significance of three vortex-shedding patterns： ωx has a greater effect on the flow fields around the sharp edges relative to the vortices generated in the 2D simulation. In the slice along the axial orientation, the vortex effect of ωy along the radial axis is smaller than that of ωx along the circumferential direction, indicating the radial effect on the velocity more pronounced than the circumferential effect around the sharp edges of the disk. The rotational interaction ωz of the fluid in the horizontal plane during the heave motion is insignificant. Based on the 2D and 3D simulation results, the turning points that separate the increasing regimes of the added mass coefficient and damping ratio are identified. The dependence of the turning point on the diameter ratio Dd/Dc and thickness ratio td/Dc are discussed in detail.
文摘The unsteady evolution of trailing vortex sheets behind a wing in ground effect is simulated using an unsteady discrete vortex panel method. The ground effect is included by image method. The present method is validated by comparing the simulated wake roll-up shapes to published numerical results. When a wing is flying in a very close proximity to the ground, the optimal wing loading is parabolic rather than elliptic. Thus, a theoretical model of wing load distributions is suggested, and unsteady vortex evolutions behind lifting lines with both elliptic and parabolic load distributions are simulated for several ground heights. For a lifting line with elliptic and parabolic loading, the ground has the effect of moving the wingtip vortices laterally outward and suppressing the development of the vortex. When the wing is in a very close proximity to the ground, the types of wing load distributions does not affect much on the overall wake shapes, but parabolic load distributions make the wingtip vortices move more laterally outward than the elliptic load distributions.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51490672 and 51761135011)the financial supports by the National Natural Science Foundation of China(Grant No.51490673)the Petro China Innovation Foundation(Grant No.2016D-5007-0601)
文摘Numerical simulations are carried out for wave action on a submerged horizontal circular cylinder by means of a viscous fluid model, and it is focused on the examination of the discrepancies between the viscous fluid results and the potential flow solutions. It is found that the lift force resulted from rotational flow on the circular cylinder is always in anti-phase with the inertia force and induces the discrepancies between the results. The influence factors on the magnitude of the lift force, especially the correlation between the stagnation-point position and the wave amplitude, and the effect of the vortex shedding are investigated by further examination on the flow fields around the cylinder. The viscous numerical calculations at different wave frequencies showed that the wave frequency has also significant influence on the wave forces. Under higher frequency and larger amplitude wave action, vortex shedding from the circular cylinder will appear and influence the wave forces on the cylinder substantially.
基金financial support from the National Natural Science Foundation of China(Nos.22208325 and 22409190)the National Key R&D Program of China(Nos.2023YFB3809400 and 2022YFE0138100)+2 种基金China Postdoctoral Science Foundation(No.2023M732964)Science and Technology Research and Development Projects of Henan Province(No.252102321029)the Cooperation Foundation of Dalian National Laboratory for Clean Energy of the Chinese Academy of Sciences(No.DNL202015).
文摘ABSTRACT:The development of highly sensitive and rapidresponse/recovery room-temperature NH_(3) sensors is critically demanded for environmental monitoring and healthcare diagnostics,yet remains scientifically challenging.Inspired by the two-dimensional ordered macroporous structure of peacock feathers,two-dimensional inverse opal(2DIO)polyaniline/silver(PANI/Ag)composites were fabricated via a sacrificial templating method.By integrating the advantages of gas diffusion of highly ordered macroporous structures with the catalytic activity of Ag,significant improvements in NH_(3) sensing performance were achieved.Computational fluid dynamics(CFD)simulations demonstrated that the 2DIO structure induced vortex effects,which significantly reduced the gas velocity.Concurrently,macroporous channels(~240 nm diameter)enhanced adsorption/desorption kinetics.The fabricated 2DIO PANI/Ag sensor exhibited a remarkable response of 1153%to 100 ppm NH_(3),with ultra-fast response/recovery times of 3 s/56 s,exhibiting a 420-fold improvement in response/recovery speed compared to pure PANI(126 s/325 s).A further developed wearable detection module successfully discriminated exhalation signals between simulated chronic kidney disease(CKD)patients and healthy individuals,providing a new strategy for noninvasive medical diagnosis.In-situ Fourier transform infrared spectroscopy(in-situ FT-IR)real-time tracking of NH_(3) adsorption/desorption processes confirms a chemisorption-dominated sensing mechanism.Density functional theory(DFT)calculations showed that the charge transfer at the PANI/Ag interface enhanced the adsorption of NH_(3),which significantly enhanced the molecular affinity.This study provides a viable pathway for developing high-performance flexible NH_(3) gas sensors through an interdisciplinary approach combining structural bionics,simulation optimization,theoretical analysis,and experimental validation.
