With Zunyi CINRAD/CD Doppler radar data and other data,a hail wind and heavy rainfall in short time occurred on July 10,2008 in northern Guizhou Province was analyzed in this study.The results showed that the system w...With Zunyi CINRAD/CD Doppler radar data and other data,a hail wind and heavy rainfall in short time occurred on July 10,2008 in northern Guizhou Province was analyzed in this study.The results showed that the system was affected by the southward of cold air pressure in a low-shear vortex zone.Echo monomer initially developed and arranged along the shear line,and there was hail weather in echo location with intense development.Before the hail shooting,the strongest echo value was 60-65 dBz.When the hail shooting,the low-elevation echo intensity sharply increased to 55-60 dBz with echo height of 11-15 km and VIL values>35 kg/m2,and its echo distribution showed band characteristics of vortex.When the vortex center moved to the original echo,echo intensity increased,resulting in a profound and lasting convergence of cyclones,and hail or strong wind occurred on the ground.Hail and strong short-term precipitation in towns of northern Renhuai might be related to the left inverted U-terrain.Echoes from Yongxing and Yuquan in Meitan,Xuekong and Xitou in Renhuai were the supercell echoes,and other regional hail shooting echoes were strong multi-monomer echoes.展开更多
A gate valve is one of the main elements of a circular pipeline, but the flow characteristics around the gate valve are hardly known. In this study, clarification of the flow field in front of the gate valve model in ...A gate valve is one of the main elements of a circular pipeline, but the flow characteristics around the gate valve are hardly known. In this study, clarification of the flow field in front of the gate valve model in a pipe flow via flow visualization and PIV analysis was attempted. As a result, four kinds of steady necklace-type vortex systems, 2-vortex, 4-vortex, 6-vortex and 8-vortex systems, were clearly observed in a Reynolds number between 290 and 2130. In addition, the main vortex was observed in the Reynolds number range between 2130 and 4870 with difficulty. On this account, both the center position and vorticity in the main vortex are presented against Reynolds number.展开更多
In this paper, a free-space vortex channel model of the radio vortex system is proposed to describe the propagation characteristics of vortex signals over the vortex channel. The key idea is to combine the Laguerre-Ga...In this paper, a free-space vortex channel model of the radio vortex system is proposed to describe the propagation characteristics of vortex signals over the vortex channel. The key idea is to combine the Laguerre-Gaussian(LG) modes in the optical field with the free-space propagation model in the radio field. The proposed free-space vortex channel model is derived from the electric field expression of the LG modes and the freespace channel transfer function of the freespace propagation model theoretically. Simulation results verify that the proposed model could reflect the vortex channel characteristics better than the currently used free-space propagation model.展开更多
Two kinds of symplectic schemes are proposed for the equations of vortex system in half plane.One is the Reflecting-method which is based on the symplectic schemes for the system in the whole plane.The other is constr...Two kinds of symplectic schemes are proposed for the equations of vortex system in half plane.One is the Reflecting-method which is based on the symplectic schemes for the system in the whole plane.The other is constructed directly according to the feature of the system.Aseries of numerical results are presented to show the effectiveness of our schemes.展开更多
We study the ground state of a two-dimensional vortex system with random pinnings by cooling the vortex system to zero temperature.The peak of structure factor S(k)of vortices increases with vortex density B but decre...We study the ground state of a two-dimensional vortex system with random pinnings by cooling the vortex system to zero temperature.The peak of structure factor S(k)of vortices increases with vortex density B but decreases with pin density BФ,indicating that the vortex lattice becomes better and better ordered with increasing B.When B>BФ,the triangular vortex lattice is observed away from the pins.Repulsive vortex interactions destroy the Mott insulator phase which is predicted to occur at B=BФ.The crossover line between the strong Bose glass and the weak Bose glass is nearly independent of BФfor small BФ.展开更多
Various properties of a necklace vortex system formed around a rectangular plate standing vertically on a flat ground wall were investigated by visualizations produced by injecting fluorescent dye into a water channel...Various properties of a necklace vortex system formed around a rectangular plate standing vertically on a flat ground wall were investigated by visualizations produced by injecting fluorescent dye into a water channel flow. As a result, it was found that the necklace vortex pattern had three steady systems depending on the Reynolds number Reh, the relative height h/δ of the rectangular plate compared with the laminar boundary layer thickness and the aspect ratio w/h. As it is expected that the aspect ratio of the rectangular plate will typify the projected area configuration of various three-dimensional bodies, the aspect ratio is varied widely from 0.5 to 7.0. The transitional boundaries of Reh and h/δ in the 2-vortex, 4-vortex and 6-vortex systems for each aspect ratio decreased when w/h < 3.0, and increased when w/h ≥ 3.0 as w/h increased. The x-direction length of the main vortex position XV1/h was almost constant when w/h < 3.0, and decreased when w/h ≥ 3.0 as Reh increased. Then, the separation length r1/h increased when w/h < 3.0 and Reh < 1000, and became almost constant when w/h ≥ 3.0 and Reh ≥ 1000 as w/h and Reh increased. Moreover, the increase of r1/h is notably rapid when w/h < 3.0.展开更多
The purpose of the paper is to clarify the mechanism of generation and collapse of a longitudinal vortex system induced around the leading edge of a delta wing. CFD captured well characteristics of flow structure of t...The purpose of the paper is to clarify the mechanism of generation and collapse of a longitudinal vortex system induced around the leading edge of a delta wing. CFD captured well characteristics of flow structure of the vortex system. It is found that the vortex system has a cone-shaped configuration, and both rotational velocity and vorticity have their largest values at the tip of the vortex and reduce downstream along the vortical axis. This resulted in inducing the largest negative pressure at the tip of the delta wing surface. The collapse of the vortex system was also studied. The system can still remain until the tip angle of 110 degrees. However, between 110 degrees and 120 degrees, the system becomes unstable. Over 120 degrees, the characteristics of the vortex are considered to have converted from the longitudinal vortex to the transverse one.展开更多
Flow around the front pillar of an automobile is typical of a flow field with separated and reattached flow by a vortex system. It is known that the vortex system causes the greatest aerodynamic sound around a vehicle...Flow around the front pillar of an automobile is typical of a flow field with separated and reattached flow by a vortex system. It is known that the vortex system causes the greatest aerodynamic sound around a vehicle. The objective of the present study is to clarify the relationship between vortical structures and aerodynamic sound by the vortex system generated around the front pillar. The vortex system consists of the longitudinal and the transverse system. The characteristics of the longitudinal vortex system were investigated in comparison with the transverse one. Two vortex systems were reproduced by three-dimensional delta wings. The flow visualization experiment and the computational fluid dynamics (CFD) captured well the characteristics of the flow structure of the two vortex systems. These results showed that the longitudinal with the rotating axis along mean flow direction had cone-shaped configuration whereas the transverse with the rotating axis vertical to mean flow direction had elliptic one. Increasing the tip angles of the wings from 40 to 140 degrees, there first exists the longitudinal vortex system less than 110 degrees, with the transition region ranging from 110 to 120 degrees, and finally over 120 degrees the transverse appears. The characteristics of aerodynamic sound radiated from the two vortex systems were investigated in low Mach numbers, high Reynolds number turbulent flows in the lownoise wind tunnel. As a result, it was found that the aerodynamic sound radiated from both the longitudinal and the transverse vortex system was proportional to the fifth from sixth power of mean flow velocity, and that the longitudinal vortex generated the aerodynamic sound larger than the transverse.展开更多
The vortex dynamics after the initial ring dark solitons in two-component ultracold Rydberg atomic systems have been investigated.The two parameters characterizing the Rydberg long-range interaction—namely,the Rydber...The vortex dynamics after the initial ring dark solitons in two-component ultracold Rydberg atomic systems have been investigated.The two parameters characterizing the Rydberg long-range interaction—namely,the Rydberg strength and the blockade radius—along with the initial depth,are identified as the main factors that affect the vortex dynamics.In the absence of Rydberg soft-core potential and spin-orbit coupling,the late vortex dipoles move along x-or y-axis first.However,this work demonstrates that,with certain Rydberg strength and blockade radius,the late vortex dipoles move towards the edge at an oblique angle to the coordinate axes,and it reveals that the Rydberg nonlocal nonlinear interaction shortens the lifetime of late vortices.When the intra-component and inter-component Rydberg strengths are different,the backgrounds of the two components gradually complement each other,and the lifetime of late vortices is significantly shortened.The presented results show that the Rydberg dressing breaks the rule that the initial average depth determines the number and paths of vortices.The motion features of vortex dipoles in the ultracold Rydberg atomic system have been ascertained,and their directions of movement can be predicted to some degree based on the rotation directions and initial positions of the vortices.展开更多
We present a theoretical scheme to realize two-dimensional(2D)asymmetric diffraction grating in a five-level inverted Y-type asymmetric double semiconductor quantum wells(SQWs)structure with resonant tunneling.The SQW...We present a theoretical scheme to realize two-dimensional(2D)asymmetric diffraction grating in a five-level inverted Y-type asymmetric double semiconductor quantum wells(SQWs)structure with resonant tunneling.The SQW structure interacts with a weak probe laser field,a spatially independent 2D standing-wave(SW)field,and a Laguerre–Gaussian(LG)vortex field,respectively.The results indicate that the diffraction patterns are highly sensitive to amplitude modulation and phase modulation.Because of the existence of vortex light,it is possible to realize asymmetric high-order diffraction in the SQW structure,and then a 2D asymmetric grating is established.By adjusting the detunings of the probe field,vortex field,and SW field,as well as the interaction length,diffraction intensity,and direction of the 2D asymmetric electromagnetically induced grating(EIG)can be controlled effectively.In addition,the number of orbital angular momenta(OAM)and beam waist parameter can be used to modulate the diffraction intensity and energy transfer of the probe light in different regions.High-order diffraction intensity is enhanced and high-efficiency 2D asymmetric diffraction grating with different diffraction patterns is obtained in the scheme.Such 2D asymmetric diffraction grating may be beneficial to the research of optical communication and innovative semiconductor quantum devices.展开更多
This study examines the dynamics of axis-offset collisions between two vortex rings using particle image velocimetry(PIV)measurements.At a fixed Reynolds number,the influence of axial separation on the flow evolution ...This study examines the dynamics of axis-offset collisions between two vortex rings using particle image velocimetry(PIV)measurements.At a fixed Reynolds number,the influence of axial separation on the flow evolution is systematically investigated.Finite-time Lyapunov exponent(FTLE)fields and combined vorticity-velocity analyses reveal three distinct interaction regimes.(1)In the collision and radial outflow regime(H/R_(ring)0.893,where H is the axial separation distance and R_(ring)is the ring radius),vortex rings undergo axial compression and generate strong radial outflows,with negligible material exchange between oppositely signed vortices.(2)In the collision and rebound regime(H/R_(ring)=1.786),the rings—bearing the same sign—experience a near-elastic rebound,leading to disintegration without reconnection.(3)In the merging-splitting and recovery regime(H/R_(ring)=2.679),the rings exhibit transient merging followed by splitting and coherence recovery,accompanied by significant material exchange.For even larger offsets(H/R_(ring)=3.572),interactions are negligible.These findings categorize axis-offset vortex ring interactions into three regimes based on flow behavior and yield insights relevant to enhanced mixing and heat dissipation in engineering applications.展开更多
This paper proposes a passive control method to reduce peak values of slipstream and turbulent kinetic energy in a high-speed train wake by attaching vortex generators(VGs)onto the upper surface of the tail car.The im...This paper proposes a passive control method to reduce peak values of slipstream and turbulent kinetic energy in a high-speed train wake by attaching vortex generators(VGs)onto the upper surface of the tail car.The impact of the VGs is assessed through the improved delayed detached eddy simulations(IDDES)after validating predictions against previous experimental measurements and other numerical predictions for the base case.The simulations indicate that strategically installed VGs can reduce the average slipstream velocity(U slipstream)and the upper limit of slipstream velocity(U_(slipstream,max))by~17%and~15%,respectively,as well as moving the peaks downstream by approximately train height,thus reducing the danger posed by slipstream to waiting passengers and trackside workers.Analysis shows that the wake turbulent kinetic energy diminishes as the vortex generators decelerate the downwash flow and reduce shear production in the wake.It is also found that the presence of VGs significantly impacts the flow on the upper surface near the tail by modifying the unsteady trailing longitudinal vortices through the formation of additional counter-rotating longitudinal vortices from the VGs.These latter vortices prevent the merging of vortical airflow around the trailing nose tip,which is otherwise induced by the longitudinal vortex of the train.They also reduce vortex intensity through cross-annihilation and cross diffusion as the wake advects downstream,limiting outwards advection through interaction with the image pair,and contributing to a decrease in the peak slipstream value.The method proposed offers a simple approach to wake control leading to significant slipstream benefits.展开更多
This paper examines a model that combines vortex generators and leading-edge tubercles for controlling the laminar separation bubble(LSB)over an airfoil at low Reynolds numbers(Re).This new concept of passive flow con...This paper examines a model that combines vortex generators and leading-edge tubercles for controlling the laminar separation bubble(LSB)over an airfoil at low Reynolds numbers(Re).This new concept of passive flow control technique utilizing a tubercle and vortex generator(VG)close to the leading edge was analyzed numerically for a NACA0015 airfoil.In this study,the Shear Stress Transport(SST)turbulence model was employed in the numerical modelling.Numerical modelling was completed using the ANSYS-Fluent 18.2 solver.Analyses were conducted to investigate the flow pattern and understand the underlying LSB control phenomena that enabled the new passive flow control method to provide this significant performance benefit.The findings indicated that the new concept of passive flow control technique suppressed the formation of an LSB at the suction surface of the NACA0015 airfoil,resulting in a higher lift coefficient and improved aerodynamic performance.Improvements in LSB dynamics and aerodynamic performance through the passive flow control method lead to increased energy output and enhanced stability.展开更多
Based on the temperature of the black body (TBB),station observed and NCEP reanalysis data,the impacts of the eastward propagation of convective cloud systems over the Tibetan Plateau on the southwest vortex (SWV) for...Based on the temperature of the black body (TBB),station observed and NCEP reanalysis data,the impacts of the eastward propagation of convective cloud systems over the Tibetan Plateau on the southwest vortex (SWV) formation that occurred at 1800 UTC on 29 June 2003 are analyzed by using the Zwack-Okossi (Z-O) equation to diagnose the thermal and dynamic processes.It is found that,in summer,severe convective activities often occur over the Tibetan Plateau due to the abundant supply of moisture.The convective cloud near the east edge of the plateau could move eastward with a shortwave trough in the westerly.The divergent center that is induced by latent heat release,which is associated with severe convective activities,moves out with the convective cloud and contributes to the low level decompression which is favorable for the formation of plateau edge cyclogenesis (PEC).The Z-O equation indicates that,in this case,the latent heat release and convergence are the two most important factors for SWV formation,which amounts to about 42% and 15% of the term TOTAL,respectively.It is implied that the thermal process effect was more important than the dynamic process during SWV formation.展开更多
The performance of compact,aggressive ducts in advanced propulsion systems is limited by the internal flow separation coupled with the formation of secondary counter-rotating vortices that give rise to intensive flow ...The performance of compact,aggressive ducts in advanced propulsion systems is limited by the internal flow separation coupled with the formation of secondary counter-rotating vortices that give rise to intensive flow distortions at the duct exit.An experimental investigation was conducted to study the flow field and passive suppression of flow separation and Aerodynamic Interface Plane (AIP) distortion in a serpentine air inlet duct.Tests were performed by a turbofan engine at several Engine Operating Points (EOPs) from 56%(idle) to 100%(max).A large total pressure deficit region arose at the upper part of the AIP,which was associated with the upper surface flow separation.Using the new mechanical S-type vortex generators in two longitudinal positions (VGl and VG2),separation and loss were diminished at the upper part of the duct and AIP.The VG2 arrangement attained the maximum reductions in distortion coefficients which were 73.72%,60.7% and 37.8% in DC(90°),DC(60°) and△P_C/P metrics,respectively.In the next step of the study,some unsteady aspects of the flow field were analyzed inside the duct.The separation onset and reattachment points were determined by the standard deviation of static pressure on the upper surface.The AIP spectral distribution showed that the boundary of low pressure and high pressure recovery regions was dominated by the maximum fluctuations.Furthermore,the PSD diagram of several probes at AIP revealed the vortex shedding frequency and its higher harmonics at separation region.The energy content of distinct unsteady spectral features in the bare configuration was significantly reduced using VGs,which showed the improvement of flow at the duct exit.展开更多
Sail is the core part of autonomous sailboat and wing sail is a new type of sail. Wing sail generates not only propulsion but also lateral force and heeling moment. The latter two will affect the navigation status and...Sail is the core part of autonomous sailboat and wing sail is a new type of sail. Wing sail generates not only propulsion but also lateral force and heeling moment. The latter two will affect the navigation status and bring resistance. Double sail can effectively reduce the center of wind pressure and heeling moment. In order to study the effect of distance between two sails, airfoil and attack angle on the total lift coefficient of double sail propulsion system, pressure coefficient distribution and lift coefficient calculation model have been established based on vortex panel method. By using the basic finite solution, the fluid dynamic forces on the two-dimensional sails are computed.The results show that, the distance in the range of 0 to 1 time chord length, when using the same airfoil in the fore and aft sail, the total lift coefficient of the double sail increases with the increase of distance, finally reaches a stable value in the range of one to three times chord length. Lift coefficients of thicker airfoils are more sensitive to the change of distance. The thicker the airfoil, the longer distance is required of the total lift coefficient toward stable.When different airfoils are adopted in fore and aft sail, the total lift coefficient increases with the increase of the thickness of aft sail. The smaller the thickness difference is, the more sensitive to the distance change the lift coefficient is. The thinner the fore sail is, the lower the influence will be on the lift coefficient of aft sail.展开更多
We propose an approach for generating robust two-dimensional(2D)vortex clusters(VCs)in a Rydberg atomic system by utilizing parity-time(PT)symmetric optical Bessel potential.We show that the system supports novel mult...We propose an approach for generating robust two-dimensional(2D)vortex clusters(VCs)in a Rydberg atomic system by utilizing parity-time(PT)symmetric optical Bessel potential.We show that the system supports novel multicore VCs with four and eight cores,corresponding to topological charges 2 and 4,respectively.The stability of these VCs can be dynamically adjusted through the manipulation of the gain-loss component,Kerr nonlinearities,and the degree of nonlocality inherent in the Rydberg atoms.These VCs are confined within the first lattice well of the Bessel potential,and both the power and width of lights undergo a quasi-periodic breathing phenomenon,which is attributed to the power exchange between the light fields and Bessel potential.Both self-attractive and self-repulsive Kerr interactions can sustain robust VCs within this system.The insights presented here not only facilitate the creation and manipulation of 2D VCs through PT-symmetric potentials but also pave the way for potential applications in optical information processing and transmission.展开更多
Strong free-surface water vortices are found throughout industrial hydraulic systems used for water treatment,flow regulation,and energy generation.Previous models using the volumetric flow rate as a model input have ...Strong free-surface water vortices are found throughout industrial hydraulic systems used for water treatment,flow regulation,and energy generation.Previous models using the volumetric flow rate as a model input have generally been semi-empirical,and have tended to have some limitations in terms of the design of practical hydropower systems.In this study,an analytical model of a strong free-surface water vortex was developed.This model only requires the water head and geometric parameters as its inputs and calculates the maximum volumetric flow rate,aircore diameter,and rotational constant.Detailed experimental depthedischarge data from a full-scale gravitational vortex hydropower system,unavailable in the relevant literature,were obtained,and the simulated results showed excellent agreement with the experimental observations.These data could be used to verify similar models using laboratory-scale physical models in order to investigate the scaling effects.In contrast to previous models,this model does not assume a constant average velocity across the vortex radius and allows precise calculation of the resultant velocity vectors.Therefore,this model presents advantages in turbine design for energy generation systems.展开更多
We propose a theoretical scheme to realize a two-dimensional(2D)diffraction grating in a four-level inverted-Y-type atomic system coupled by a standing-wave(SW)field and a Laguerre-Gaussian(LG)vortex field.Owing to as...We propose a theoretical scheme to realize a two-dimensional(2D)diffraction grating in a four-level inverted-Y-type atomic system coupled by a standing-wave(SW)field and a Laguerre-Gaussian(LG)vortex field.Owing to asymmetric spatial modulation of the LG vortex field,the incident probe field can be lopsidedly diffracted into four domains and an asymmetric 2D electromagnetically induced grating is created.By adjusting the detunings of the probe field and the LG vortex field,the intensities of the LG vortex field and the coherent SW field,as well as the interaction length,the diffraction properties and efficiency,can be effectively manipulated.In addition,the effect of the azimuthal parameter on the Fraunhofer diffraction of the probe field is also discussed.This asymmetric 2D diffraction grating scheme may provide a versatile platform for designing quantum devices that require asymmetric light transmission.展开更多
Vortex patterns of dust particles have been observed in a magnetized dusty plasma system. The formation mechanism of two-dimensional （2D） vortex patterns has been investigated by analysing the forces acting on dust ...Vortex patterns of dust particles have been observed in a magnetized dusty plasma system. The formation mechanism of two-dimensional （2D） vortex patterns has been investigated by analysing the forces acting on dust particles and molecular dynamics （MD） simulations in a 2D confined magnetized dusty plasma. It has been found that with a weak confining electric field and a strong magnetic field, the particles＇ trajectories will form a vortex shape. The simulation results agree with our experimental observations. In our experiments, vortex patterns can be induced via circular rotation of particles by changing the rf （radio-frequency） power in a magnetized dusty plasma.展开更多
文摘With Zunyi CINRAD/CD Doppler radar data and other data,a hail wind and heavy rainfall in short time occurred on July 10,2008 in northern Guizhou Province was analyzed in this study.The results showed that the system was affected by the southward of cold air pressure in a low-shear vortex zone.Echo monomer initially developed and arranged along the shear line,and there was hail weather in echo location with intense development.Before the hail shooting,the strongest echo value was 60-65 dBz.When the hail shooting,the low-elevation echo intensity sharply increased to 55-60 dBz with echo height of 11-15 km and VIL values>35 kg/m2,and its echo distribution showed band characteristics of vortex.When the vortex center moved to the original echo,echo intensity increased,resulting in a profound and lasting convergence of cyclones,and hail or strong wind occurred on the ground.Hail and strong short-term precipitation in towns of northern Renhuai might be related to the left inverted U-terrain.Echoes from Yongxing and Yuquan in Meitan,Xuekong and Xitou in Renhuai were the supercell echoes,and other regional hail shooting echoes were strong multi-monomer echoes.
文摘A gate valve is one of the main elements of a circular pipeline, but the flow characteristics around the gate valve are hardly known. In this study, clarification of the flow field in front of the gate valve model in a pipe flow via flow visualization and PIV analysis was attempted. As a result, four kinds of steady necklace-type vortex systems, 2-vortex, 4-vortex, 6-vortex and 8-vortex systems, were clearly observed in a Reynolds number between 290 and 2130. In addition, the main vortex was observed in the Reynolds number range between 2130 and 4870 with difficulty. On this account, both the center position and vorticity in the main vortex are presented against Reynolds number.
基金supported in part by National Science Foundation for Distinguished Young Scholars of China with Grant number 61325004Major Program of National Natural Science Foundation of Hubei in China with Grant number 2016CFA009+2 种基金the Fundamental Research Funds for the Central Universities with Grant number 2015ZDTD012the National Natural Science Foundation of China under Grant No.61463035the Research Foundation of the Education Department of Jiangxi Province under Grant No.GJJ150198
文摘In this paper, a free-space vortex channel model of the radio vortex system is proposed to describe the propagation characteristics of vortex signals over the vortex channel. The key idea is to combine the Laguerre-Gaussian(LG) modes in the optical field with the free-space propagation model in the radio field. The proposed free-space vortex channel model is derived from the electric field expression of the LG modes and the freespace channel transfer function of the freespace propagation model theoretically. Simulation results verify that the proposed model could reflect the vortex channel characteristics better than the currently used free-space propagation model.
文摘Two kinds of symplectic schemes are proposed for the equations of vortex system in half plane.One is the Reflecting-method which is based on the symplectic schemes for the system in the whole plane.The other is constructed directly according to the feature of the system.Aseries of numerical results are presented to show the effectiveness of our schemes.
基金Supported by the Ministry of Science and Technology of China(NKBRSF-G19990646)the National Natural Science Foundation of China under Grant No.19904009Zhejiang Province Scientific Foundation under Grant No.199031.
文摘We study the ground state of a two-dimensional vortex system with random pinnings by cooling the vortex system to zero temperature.The peak of structure factor S(k)of vortices increases with vortex density B but decreases with pin density BФ,indicating that the vortex lattice becomes better and better ordered with increasing B.When B>BФ,the triangular vortex lattice is observed away from the pins.Repulsive vortex interactions destroy the Mott insulator phase which is predicted to occur at B=BФ.The crossover line between the strong Bose glass and the weak Bose glass is nearly independent of BФfor small BФ.
文摘Various properties of a necklace vortex system formed around a rectangular plate standing vertically on a flat ground wall were investigated by visualizations produced by injecting fluorescent dye into a water channel flow. As a result, it was found that the necklace vortex pattern had three steady systems depending on the Reynolds number Reh, the relative height h/δ of the rectangular plate compared with the laminar boundary layer thickness and the aspect ratio w/h. As it is expected that the aspect ratio of the rectangular plate will typify the projected area configuration of various three-dimensional bodies, the aspect ratio is varied widely from 0.5 to 7.0. The transitional boundaries of Reh and h/δ in the 2-vortex, 4-vortex and 6-vortex systems for each aspect ratio decreased when w/h < 3.0, and increased when w/h ≥ 3.0 as w/h increased. The x-direction length of the main vortex position XV1/h was almost constant when w/h < 3.0, and decreased when w/h ≥ 3.0 as Reh increased. Then, the separation length r1/h increased when w/h < 3.0 and Reh < 1000, and became almost constant when w/h ≥ 3.0 and Reh ≥ 1000 as w/h and Reh increased. Moreover, the increase of r1/h is notably rapid when w/h < 3.0.
文摘The purpose of the paper is to clarify the mechanism of generation and collapse of a longitudinal vortex system induced around the leading edge of a delta wing. CFD captured well characteristics of flow structure of the vortex system. It is found that the vortex system has a cone-shaped configuration, and both rotational velocity and vorticity have their largest values at the tip of the vortex and reduce downstream along the vortical axis. This resulted in inducing the largest negative pressure at the tip of the delta wing surface. The collapse of the vortex system was also studied. The system can still remain until the tip angle of 110 degrees. However, between 110 degrees and 120 degrees, the system becomes unstable. Over 120 degrees, the characteristics of the vortex are considered to have converted from the longitudinal vortex to the transverse one.
文摘Flow around the front pillar of an automobile is typical of a flow field with separated and reattached flow by a vortex system. It is known that the vortex system causes the greatest aerodynamic sound around a vehicle. The objective of the present study is to clarify the relationship between vortical structures and aerodynamic sound by the vortex system generated around the front pillar. The vortex system consists of the longitudinal and the transverse system. The characteristics of the longitudinal vortex system were investigated in comparison with the transverse one. Two vortex systems were reproduced by three-dimensional delta wings. The flow visualization experiment and the computational fluid dynamics (CFD) captured well the characteristics of the flow structure of the two vortex systems. These results showed that the longitudinal with the rotating axis along mean flow direction had cone-shaped configuration whereas the transverse with the rotating axis vertical to mean flow direction had elliptic one. Increasing the tip angles of the wings from 40 to 140 degrees, there first exists the longitudinal vortex system less than 110 degrees, with the transition region ranging from 110 to 120 degrees, and finally over 120 degrees the transverse appears. The characteristics of aerodynamic sound radiated from the two vortex systems were investigated in low Mach numbers, high Reynolds number turbulent flows in the lownoise wind tunnel. As a result, it was found that the aerodynamic sound radiated from both the longitudinal and the transverse vortex system was proportional to the fifth from sixth power of mean flow velocity, and that the longitudinal vortex generated the aerodynamic sound larger than the transverse.
基金supported by the Natural Science Foundation of Hubei Province of China(Grant No.2025AFB370)。
文摘The vortex dynamics after the initial ring dark solitons in two-component ultracold Rydberg atomic systems have been investigated.The two parameters characterizing the Rydberg long-range interaction—namely,the Rydberg strength and the blockade radius—along with the initial depth,are identified as the main factors that affect the vortex dynamics.In the absence of Rydberg soft-core potential and spin-orbit coupling,the late vortex dipoles move along x-or y-axis first.However,this work demonstrates that,with certain Rydberg strength and blockade radius,the late vortex dipoles move towards the edge at an oblique angle to the coordinate axes,and it reveals that the Rydberg nonlocal nonlinear interaction shortens the lifetime of late vortices.When the intra-component and inter-component Rydberg strengths are different,the backgrounds of the two components gradually complement each other,and the lifetime of late vortices is significantly shortened.The presented results show that the Rydberg dressing breaks the rule that the initial average depth determines the number and paths of vortices.The motion features of vortex dipoles in the ultracold Rydberg atomic system have been ascertained,and their directions of movement can be predicted to some degree based on the rotation directions and initial positions of the vortices.
基金supported by the National Natural Science Foundation of China(Grant No.12105210)the Knowledge Innovation Program of Wuhan-Basi Research(Grant No.2023010201010149)。
文摘We present a theoretical scheme to realize two-dimensional(2D)asymmetric diffraction grating in a five-level inverted Y-type asymmetric double semiconductor quantum wells(SQWs)structure with resonant tunneling.The SQW structure interacts with a weak probe laser field,a spatially independent 2D standing-wave(SW)field,and a Laguerre–Gaussian(LG)vortex field,respectively.The results indicate that the diffraction patterns are highly sensitive to amplitude modulation and phase modulation.Because of the existence of vortex light,it is possible to realize asymmetric high-order diffraction in the SQW structure,and then a 2D asymmetric grating is established.By adjusting the detunings of the probe field,vortex field,and SW field,as well as the interaction length,diffraction intensity,and direction of the 2D asymmetric electromagnetically induced grating(EIG)can be controlled effectively.In addition,the number of orbital angular momenta(OAM)and beam waist parameter can be used to modulate the diffraction intensity and energy transfer of the probe light in different regions.High-order diffraction intensity is enhanced and high-efficiency 2D asymmetric diffraction grating with different diffraction patterns is obtained in the scheme.Such 2D asymmetric diffraction grating may be beneficial to the research of optical communication and innovative semiconductor quantum devices.
基金supported by the NSFC Excellence Research Group Program on“Multiscale Problems in Nonlinear Mechanics”(Grant No.12588201)the National Natural Science Foundation of China(Grant Nos.12432011,12102246,12422208,12372219,12502258)。
文摘This study examines the dynamics of axis-offset collisions between two vortex rings using particle image velocimetry(PIV)measurements.At a fixed Reynolds number,the influence of axial separation on the flow evolution is systematically investigated.Finite-time Lyapunov exponent(FTLE)fields and combined vorticity-velocity analyses reveal three distinct interaction regimes.(1)In the collision and radial outflow regime(H/R_(ring)0.893,where H is the axial separation distance and R_(ring)is the ring radius),vortex rings undergo axial compression and generate strong radial outflows,with negligible material exchange between oppositely signed vortices.(2)In the collision and rebound regime(H/R_(ring)=1.786),the rings—bearing the same sign—experience a near-elastic rebound,leading to disintegration without reconnection.(3)In the merging-splitting and recovery regime(H/R_(ring)=2.679),the rings exhibit transient merging followed by splitting and coherence recovery,accompanied by significant material exchange.For even larger offsets(H/R_(ring)=3.572),interactions are negligible.These findings categorize axis-offset vortex ring interactions into three regimes based on flow behavior and yield insights relevant to enhanced mixing and heat dissipation in engineering applications.
基金Project(52372370)supported by the National Natural Science Foundation of ChinaProject(2023ZZTS0379)supported by the Graduate Student Independent Innovation Project of Central South University,ChinaProject(202206370058)supported by the China Scholarship Council。
文摘This paper proposes a passive control method to reduce peak values of slipstream and turbulent kinetic energy in a high-speed train wake by attaching vortex generators(VGs)onto the upper surface of the tail car.The impact of the VGs is assessed through the improved delayed detached eddy simulations(IDDES)after validating predictions against previous experimental measurements and other numerical predictions for the base case.The simulations indicate that strategically installed VGs can reduce the average slipstream velocity(U slipstream)and the upper limit of slipstream velocity(U_(slipstream,max))by~17%and~15%,respectively,as well as moving the peaks downstream by approximately train height,thus reducing the danger posed by slipstream to waiting passengers and trackside workers.Analysis shows that the wake turbulent kinetic energy diminishes as the vortex generators decelerate the downwash flow and reduce shear production in the wake.It is also found that the presence of VGs significantly impacts the flow on the upper surface near the tail by modifying the unsteady trailing longitudinal vortices through the formation of additional counter-rotating longitudinal vortices from the VGs.These latter vortices prevent the merging of vortical airflow around the trailing nose tip,which is otherwise induced by the longitudinal vortex of the train.They also reduce vortex intensity through cross-annihilation and cross diffusion as the wake advects downstream,limiting outwards advection through interaction with the image pair,and contributing to a decrease in the peak slipstream value.The method proposed offers a simple approach to wake control leading to significant slipstream benefits.
基金the Scientific Research Projects Unit of Erciyes University under contract no:FDS-2022-11532 and FOA-2025-14773.
文摘This paper examines a model that combines vortex generators and leading-edge tubercles for controlling the laminar separation bubble(LSB)over an airfoil at low Reynolds numbers(Re).This new concept of passive flow control technique utilizing a tubercle and vortex generator(VG)close to the leading edge was analyzed numerically for a NACA0015 airfoil.In this study,the Shear Stress Transport(SST)turbulence model was employed in the numerical modelling.Numerical modelling was completed using the ANSYS-Fluent 18.2 solver.Analyses were conducted to investigate the flow pattern and understand the underlying LSB control phenomena that enabled the new passive flow control method to provide this significant performance benefit.The findings indicated that the new concept of passive flow control technique suppressed the formation of an LSB at the suction surface of the NACA0015 airfoil,resulting in a higher lift coefficient and improved aerodynamic performance.Improvements in LSB dynamics and aerodynamic performance through the passive flow control method lead to increased energy output and enhanced stability.
基金supported by the National Natural Science Foundation of China (Grant Nos. 40875021 and 40930951)the project of the State Key Laboratory of Severe Weather,Chinese Academy of Meteorological Sciences (Grant No. 2009LASW-A03)
文摘Based on the temperature of the black body (TBB),station observed and NCEP reanalysis data,the impacts of the eastward propagation of convective cloud systems over the Tibetan Plateau on the southwest vortex (SWV) formation that occurred at 1800 UTC on 29 June 2003 are analyzed by using the Zwack-Okossi (Z-O) equation to diagnose the thermal and dynamic processes.It is found that,in summer,severe convective activities often occur over the Tibetan Plateau due to the abundant supply of moisture.The convective cloud near the east edge of the plateau could move eastward with a shortwave trough in the westerly.The divergent center that is induced by latent heat release,which is associated with severe convective activities,moves out with the convective cloud and contributes to the low level decompression which is favorable for the formation of plateau edge cyclogenesis (PEC).The Z-O equation indicates that,in this case,the latent heat release and convergence are the two most important factors for SWV formation,which amounts to about 42% and 15% of the term TOTAL,respectively.It is implied that the thermal process effect was more important than the dynamic process during SWV formation.
文摘The performance of compact,aggressive ducts in advanced propulsion systems is limited by the internal flow separation coupled with the formation of secondary counter-rotating vortices that give rise to intensive flow distortions at the duct exit.An experimental investigation was conducted to study the flow field and passive suppression of flow separation and Aerodynamic Interface Plane (AIP) distortion in a serpentine air inlet duct.Tests were performed by a turbofan engine at several Engine Operating Points (EOPs) from 56%(idle) to 100%(max).A large total pressure deficit region arose at the upper part of the AIP,which was associated with the upper surface flow separation.Using the new mechanical S-type vortex generators in two longitudinal positions (VGl and VG2),separation and loss were diminished at the upper part of the duct and AIP.The VG2 arrangement attained the maximum reductions in distortion coefficients which were 73.72%,60.7% and 37.8% in DC(90°),DC(60°) and△P_C/P metrics,respectively.In the next step of the study,some unsteady aspects of the flow field were analyzed inside the duct.The separation onset and reattachment points were determined by the standard deviation of static pressure on the upper surface.The AIP spectral distribution showed that the boundary of low pressure and high pressure recovery regions was dominated by the maximum fluctuations.Furthermore,the PSD diagram of several probes at AIP revealed the vortex shedding frequency and its higher harmonics at separation region.The energy content of distinct unsteady spectral features in the bare configuration was significantly reduced using VGs,which showed the improvement of flow at the duct exit.
基金financially supported by the JIANG Xinsong Innovation Fund(Grant No.Y8F7010701)
文摘Sail is the core part of autonomous sailboat and wing sail is a new type of sail. Wing sail generates not only propulsion but also lateral force and heeling moment. The latter two will affect the navigation status and bring resistance. Double sail can effectively reduce the center of wind pressure and heeling moment. In order to study the effect of distance between two sails, airfoil and attack angle on the total lift coefficient of double sail propulsion system, pressure coefficient distribution and lift coefficient calculation model have been established based on vortex panel method. By using the basic finite solution, the fluid dynamic forces on the two-dimensional sails are computed.The results show that, the distance in the range of 0 to 1 time chord length, when using the same airfoil in the fore and aft sail, the total lift coefficient of the double sail increases with the increase of distance, finally reaches a stable value in the range of one to three times chord length. Lift coefficients of thicker airfoils are more sensitive to the change of distance. The thicker the airfoil, the longer distance is required of the total lift coefficient toward stable.When different airfoils are adopted in fore and aft sail, the total lift coefficient increases with the increase of the thickness of aft sail. The smaller the thickness difference is, the more sensitive to the distance change the lift coefficient is. The thinner the fore sail is, the lower the influence will be on the lift coefficient of aft sail.
基金Project supported by the National Natural Science Foundation of China(Grant No.62275075)the Science and Technology Research Program of the Education Department of Hubei Province,China(Grant No.B2022188)+2 种基金the Natural Science Foundation of Hubei Province,China(Grant No.2023AFC042)the Training Program of Innovation and Entrepreneurship for Undergraduates of Hubei Province,China(Grant No.S202210927003)the Medical Project of Hubei University of Science and Technology(Grant No.2023YKY08)。
文摘We propose an approach for generating robust two-dimensional(2D)vortex clusters(VCs)in a Rydberg atomic system by utilizing parity-time(PT)symmetric optical Bessel potential.We show that the system supports novel multicore VCs with four and eight cores,corresponding to topological charges 2 and 4,respectively.The stability of these VCs can be dynamically adjusted through the manipulation of the gain-loss component,Kerr nonlinearities,and the degree of nonlocality inherent in the Rydberg atoms.These VCs are confined within the first lattice well of the Bessel potential,and both the power and width of lights undergo a quasi-periodic breathing phenomenon,which is attributed to the power exchange between the light fields and Bessel potential.Both self-attractive and self-repulsive Kerr interactions can sustain robust VCs within this system.The insights presented here not only facilitate the creation and manipulation of 2D VCs through PT-symmetric potentials but also pave the way for potential applications in optical information processing and transmission.
文摘Strong free-surface water vortices are found throughout industrial hydraulic systems used for water treatment,flow regulation,and energy generation.Previous models using the volumetric flow rate as a model input have generally been semi-empirical,and have tended to have some limitations in terms of the design of practical hydropower systems.In this study,an analytical model of a strong free-surface water vortex was developed.This model only requires the water head and geometric parameters as its inputs and calculates the maximum volumetric flow rate,aircore diameter,and rotational constant.Detailed experimental depthedischarge data from a full-scale gravitational vortex hydropower system,unavailable in the relevant literature,were obtained,and the simulated results showed excellent agreement with the experimental observations.These data could be used to verify similar models using laboratory-scale physical models in order to investigate the scaling effects.In contrast to previous models,this model does not assume a constant average velocity across the vortex radius and allows precise calculation of the resultant velocity vectors.Therefore,this model presents advantages in turbine design for energy generation systems.
基金supported by the National Natural Science Foundation of China (grant no. 12105210)the Knowledge Innovation Program of Wuhan-Basic Research (grant no. 2023010201010149)
文摘We propose a theoretical scheme to realize a two-dimensional(2D)diffraction grating in a four-level inverted-Y-type atomic system coupled by a standing-wave(SW)field and a Laguerre-Gaussian(LG)vortex field.Owing to asymmetric spatial modulation of the LG vortex field,the incident probe field can be lopsidedly diffracted into four domains and an asymmetric 2D electromagnetically induced grating is created.By adjusting the detunings of the probe field and the LG vortex field,the intensities of the LG vortex field and the coherent SW field,as well as the interaction length,the diffraction properties and efficiency,can be effectively manipulated.In addition,the effect of the azimuthal parameter on the Fraunhofer diffraction of the probe field is also discussed.This asymmetric 2D diffraction grating scheme may provide a versatile platform for designing quantum devices that require asymmetric light transmission.
基金'the Research Start-Up Fund of China Agricultural University(No.2005057)
文摘Vortex patterns of dust particles have been observed in a magnetized dusty plasma system. The formation mechanism of two-dimensional （2D） vortex patterns has been investigated by analysing the forces acting on dust particles and molecular dynamics （MD） simulations in a 2D confined magnetized dusty plasma. It has been found that with a weak confining electric field and a strong magnetic field, the particles＇ trajectories will form a vortex shape. The simulation results agree with our experimental observations. In our experiments, vortex patterns can be induced via circular rotation of particles by changing the rf （radio-frequency） power in a magnetized dusty plasma.
