To explore the relationship between dynamic characteristics and wake patterns,numerical simulations were conducted on three equal-diameter cylinders arranged in an equilateral triangle.The simulations varied reduced v...To explore the relationship between dynamic characteristics and wake patterns,numerical simulations were conducted on three equal-diameter cylinders arranged in an equilateral triangle.The simulations varied reduced velocities and gap spacing to observe flow-induced vibrations(FIVs).The immersed boundary–lattice Boltzmann flux solver(IB–LBFS)was applied as a numerical solution method,allowing for straightforward application on a simple Cartesian mesh.The accuracy and rationality of this method have been verified through comparisons with previous numerical results,including studies on flow past three stationary circular cylinders arranged in a similar pattern and vortex-induced vibrations of a single cylinder across different reduced velocities.When examining the FIVs of three cylinders,numerical simulations were carried out across a range of reduced velocities(3.0≤Ur≤13.0)and gap spacing(L=3D,4D,and 5D).The observed vibration response included several regimes:the desynchronization regime,the initial branch,and the lower branch.Notably,the transverse amplitude peaked,and a double vortex street formed in the wake when the reduced velocity reached the lower branch.This arrangement of three cylinders proved advantageous for energy capture as the upstream cylinder’s vibration response mirrored that of an isolated cylinder,while the response of each downstream cylinder was significantly enhanced.Compared to a single cylinder,the vibration and flow characteristics of this system are markedly more complex.The maximum transverse amplitudes of the downstream cylinders are nearly identical and exceed those observed in a single-cylinder set-up.Depending on the gap spacing,the flow pattern varied:it was in-phase for L=3D,antiphase for L=4D,and exhibited vortex shedding for L=5D.The wake configuration mainly featured double vortex streets for L=3D and evolved into two pairs of double vortex streets for L=5D.Consequently,it well illustrates the coupling mechanism that dynamics characteristics and wake vortex change with gap spacing and reduced velocities.展开更多
The lattice Boltzmann method(LBM)is employed to simulate flow around two staggered cylinders within a confined channel.The numerical model is validated against existing experimental data by comparing drag coefficients...The lattice Boltzmann method(LBM)is employed to simulate flow around two staggered cylinders within a confined channel.The numerical model is validated against existing experimental data by comparing drag coefficients and Strouhal numbers in the single-cylinder configuration.The study systematically investigates the influence of vertical(h)and horizontal(l)spacing between the cylinders,as well as the Reynolds number(Re=0.1–160),on the hydrodynamic forces,streamline patterns,and vortex dynamics.Results indicate that reducing the horizontal spacing l suppresses flow separation behind the upstream cylinder,while either excessively small or large vertical spacing h diminishes separation in the downstream cylinder.The onset of periodic vortex shedding is delayed due to inter-cylinder interactions,with the critical Reynolds number increasing to Rec=71–112,significantly higher than that of a single-cylinder case(Re_(c)≈69).During the vortex shedding regime,the downstream cylinder exhibits a greater lift force fluctuation compared to the upstream cylinder.At Re=160,the root-mean-square lift coefficient(C′_(L))ranges from approximately 0.17 to 0.56 for the downstream cylinder,and from 0.018 to 0.4 for the upstream one.The shedding frequency,characterized by the Strouhal number(St),increases with Reynolds number,reaching St=0.12–0.18 at Re=160.Variations in h and l significantly influence St,with a decrease in l or an increase in h lowering the shedding frequency—this effect is more pronounced in the horizontal direction.展开更多
The integrated valve-controlled cylinder combines various control and execution components in hydraulic transmission systems.Its precise control and rapid response characteristics make it widely used in mobile equipme...The integrated valve-controlled cylinder combines various control and execution components in hydraulic transmission systems.Its precise control and rapid response characteristics make it widely used in mobile equipment for aerospace,robotics,and other engineering applications.Additive manufacturing provides high design freedom which can further enhance the power density of integrated valve-controlled cylinders.However,there is a lack of effective design methods to guide the additive manufacturing of valve-controlled cylinders for more efficient hydraulic energy transmission.This study accordingly introduces an energy-saving design method based on additive manufacturing for integrated valve-controlled cylinders.The method consists of two main parts:(1)redesigning the manifold block to eliminate leakage points and reduce energy losses through integrated design of the valve,cylinder,and piping;(2)establishing a pressure loss model to achieve energy savings through optimized flow channel design for bends with different parameters.Compared to traditional valve-controlled cylinders,the integrated valvecontrolled cylinder developed from our method reduces the weight by 31%,volume by 55%,and pressure loss in the main flow channel by over 30%.This indicates that the design achieves both lightweight construction and improved hydraulic transmission efficiency.This study provides theoretical guidance for the design of lightweight and energy-efficient valve-controlled cylinders,and may aid the design of similar hydraulic machinery.展开更多
Flow characteristics around a wall-mounted square cylinder have been numerically simulated at aspect ratios (AR) ranging from 4 to 7 at Re =10 000. Four turbulence models have been compared in terms of drag coefficien...Flow characteristics around a wall-mounted square cylinder have been numerically simulated at aspect ratios (AR) ranging from 4 to 7 at Re =10 000. Four turbulence models have been compared in terms of drag coefficient (C_D). The closest result has been provided by two turbulence models, namely, k-ε Realizable and k ?ω Shear Stress Transport (SST). Hence, these models were utilized to present the flow patterns of pressure distributions, turbulent kinetic energy values, velocity magnitude values with streamlines, streamwise velocity components, crossstream velocity components and spanwise velocity components on different planes. Flow stagnation has been attained in front of the cylinder. Pressure values peaked for the upstream region. Over the cylinders, the tip vortex structure was dominant owing to the influence of the free end. Flow separation from the top front edge of the body has been obtained. The dividing streamline affected by the flow separation was highly effective in the wake region and moved nearer to the body when the aspect ratio was decreased;the reason was the wake shrinkage owing to the decreasing aspect ratio. Upwash and downwash have been seen in the cylinder wake. These two models presented similar flow patterns and drag coefficients. These drag coefficients are in good agreement with those in previous studies.展开更多
In this study,four types of spiral fins with varying parameters were mounted on an upstream cylinder,and the effects of spiral fins on the vibration response of heat exchange tubes and the vortex structure in cross fl...In this study,four types of spiral fins with varying parameters were mounted on an upstream cylinder,and the effects of spiral fins on the vibration response of heat exchange tubes and the vortex structure in cross flow were studied through experiments and numerical simulations.The results indicate a strong dependency of the cylinder's vibration response on the fin parameters.The results indicate that the vibration response and wake structure of the cylinder are significantly influenced by the parameters of the fins.The introduction of a finned cylinder affects both its own vibration amplitude and frequency,as well as the downstream cylinder.The amplitudes of finned cylinders Ⅰ and Ⅲ are reduced by 57.8% and 59.9%,respectively,compared to the bare cylinder.This reduction helps to restrain vibration and diminishes the amplitudes of the downstream cylinder.Although finned cylinder Ⅱ slightly decreases its own vibration,it increases the amplitude of the downstream cylinder by 13.7%.The mean drag coefficient and the root mean square of the lift coefficient of the finned cylinder are higher than those of the bare cylinder when the finned cylinder is positioned upstream.Smaller pitch and larger equivalent diameter will lead to increased drag,resulting in enhanced vortex shedding in the wake,which amplifies the vibrations of the cylinder in that wake.The downstream of finned cylinder Ⅱ has the widest wake and higher vortex strength,and the dynamic load and vibration of the downstream cylinder are increased.The vortex intensity decays faster in the wake of finned cylinder Ⅲ,and the vibration of the downstream cylinder is weaker.展开更多
The analysis of the characteristics of the cushion process of the pneumatic cushion cylinder is presented, and the nonlinear model of pneumatic cushion cylinders is built in the form of nonlinear differential equation...The analysis of the characteristics of the cushion process of the pneumatic cushion cylinder is presented, and the nonlinear model of pneumatic cushion cylinders is built in the form of nonlinear differential equations. Besides, through the simulation of the pressure in the cushion chamber, the characteristics of the pneumatic cushion cylinder are obtained, which helps to understand the performance of the pneumatic cushion cylinder and improve or design the better cushion structure.展开更多
In this study, the laminar heat transfer and nanofluid flow between two porous horizontal concentric cylinders was investigated. The problem is investigated in two different geometries and the Re=10, 25, 50, 75, 100 a...In this study, the laminar heat transfer and nanofluid flow between two porous horizontal concentric cylinders was investigated. The problem is investigated in two different geometries and the Re=10, 25, 50, 75, 100 and volume fraction 0, 0.2%, 0.5%, 2% and 5% that related to copper nanoparticles, and porous medium porosity of 0.5 and 0.9. Compared to the first geometry, the convective coefficient in the second geometry increases by 8.3%, 7% and 5.5% at Reynolds numbers of 100, 75 and 50, respectively. Comparison of the outlet temperatures for two heat fluxes of 300 and 1200 W/m^2 indicates a 2.5% temperature growth by a fourfold increase in the heat fluxes. Also, the higher Nusselt number is associated with the second geometry occurring at porosities of 0.9 and 0.5, respectively. In both geometries, the Nusselt number values at the porosity of 0.9 are higher, which is due to the increased nanofluid convection at higher porosities. The velocity of the nanofluid experiences a two-fold increase at the outlet compared to its inlet velocity in the first geometry and for both porosities. Similarly, a three-fold increase was achieved in the second geometry and for both porosities.展开更多
The Xu ＆ Yan scale-adaptive simulation （XYSAS） model is employed to simulate the flows past wavy cylinders at Reynolds number 8 × 10 3.This approach yields results in good agreement with experimental measureme...The Xu ＆ Yan scale-adaptive simulation （XYSAS） model is employed to simulate the flows past wavy cylinders at Reynolds number 8 × 10 3.This approach yields results in good agreement with experimental measurements.The mean flow field and near wake vortex structure are replicated and compared with that of a corresponding circular cylinder.The effects of wavelength ratios λ/D m from 3 to 7,together with the amplitude ratios a /D m of 0.091 and 0.25,are fully investigated.Owing to the wavy configuration,a maximum reduction of Strouhal number and root-meansquare （r.m.s） fluctuating lift coefficients are up to 50% and 92%,respectively,which means the vortex induced vibration （VIV） could be effectively alleviated at certain larger values of λ/D m and a /D m.Also,the drag coefficients can be reduced by 30%.It is found that the flow field presents contrary patterns with the increase of λ/D m.The free shear layer becomes much more stable and rolls up into mature vortex only further downstream when λ/D m falls in the range of 5-7.The amplitude ratio a /D m greatly changes the separation line,and subsequently influences the wake structures.展开更多
A series of three-dimensional numerical simulations is carried out to investigate the effect of inclined angle on flow behavior behind two side-by-side inclined cylinders at low Reynolds number Re=100 and small spacin...A series of three-dimensional numerical simulations is carried out to investigate the effect of inclined angle on flow behavior behind two side-by-side inclined cylinders at low Reynolds number Re=100 and small spacing ratio T/D=1.5 (T is the center-to-center distance between two side-by-side cylinders, D is the diameter of cylinder). The instantaneous and time-averaged flow fields, force coefficients and Strouhal numbers are analyzed. Special attention is focused on the axial flow characteristics with variation of the inclined angle. The results show that the inclined angle has a significant effect on the gap flow behaviors behind two inclined cylinders. The vortex shedding behind two cylinders is suppressed with the increase of the inclined angle as well as the flip-flop gap flow. Moreover, the mean drag coefficient, root-mean-square lift coefficient and Strouhal numbers decrease monotonously with the increase of the inclined angle, which follows the independent principle at small inclined angles.展开更多
In this paper, flow around two circular cylinders in tandem arrangement with unequal diameters has been investigated using the particle image velocimetry technique(PIV) in a water channel. The upstream to downstream d...In this paper, flow around two circular cylinders in tandem arrangement with unequal diameters has been investigated using the particle image velocimetry technique(PIV) in a water channel. The upstream to downstream diameter ratio was kept constant at d/D = 2/3, the centre-to-centre distance was varied from 1.2D to 5D and the Reynolds number was varied from 1200 to 4800. The flow characteristics were analyzed through ensemble-averaged patterns of velocity, vorticity, normalized Reynolds stress contours and streamlines. Based on ensemble-averaged and instantaneous flow fields, different flow patterns, including single-wakeshedding at small spacing ratio, bi-stable flow behavior(alternating behavior of reattachment and vortex shedding) at intermediate spacing ratio and co-shedding pattern at large spacing ratio were observed. The effects of Reynolds number and the centre-to-centre spacing ratio on flow patterns and turbulent characteristics were also investigated. It was found that the diameter ratio appears to have a certain effect on the flow patterns at intermediate spacing ratios, where the reattachment of shear layer depends on the lateral width of the wake flow in the lee of the upstream cylinder. Extensive discussion on the distributions of Reynolds stress and turbulent kinetic energy was presented.展开更多
The flow past two tandem circular cylinders of different diameters was simulated using the finite volume method. The diameter of the downstream main cylinder （D） was kept constant, and the diameter of the upstream c...The flow past two tandem circular cylinders of different diameters was simulated using the finite volume method. The diameter of the downstream main cylinder （D） was kept constant, and the diameter of the upstream control cylinder （d） varied from 0.1D to D. The studied Reynolds numbers based on the diameter of the downstream main cylinder were 100 and 150. The gap between the control cylinder and the main cylinder （G） ranged from 0.1D to 4D. It is concluded that the gap-to-diameter ratio （G/D） and the diameter ratio between the two cylinders （d/D） have important effects on the drag and lift coefficients, pressure distributions around the cylinders, vortex shedding frequencies from the two cylinders, and flow characteristics.展开更多
The finite element method （FEM） is employed to analyze the resonant oscillations of the liquid confined within multiple or an array of floating bodies with fully nonlinear boundary conditions on the free surface and...The finite element method （FEM） is employed to analyze the resonant oscillations of the liquid confined within multiple or an array of floating bodies with fully nonlinear boundary conditions on the free surface and the body surface in two dimensions. The velocity potentials at each time step are obtained through the FEM with 8-node quadratic shape functions. The finite element linear system is solved by the conjugate gradient （CG） method with a symmetric successive overelaxlation （SSOR） preconditioner. The waves at the open boundary are absorbed by the combination of the damping zone method and the Sommerfeld-Orlanski equation. Numerical examples are given by an array of floating wedge- shaped cylinders and rectangular cylinders. Results are provided for heave motions including wave elevations, profiles and hydrodynamic forces. Comparisons are made in several cases with the results obtained from the second order solution in the time domain. It is found that the wave amplitude in the middle region of the array is larger than those in other places, and the hydrodynamic force on a cylinder increases with the cylinder closing to the middle of the array.展开更多
Based on model tests, the lift and resultant forces on small square cylinders caused by waves (regular and irregular) and currents are analyzed in this paper. The lift and resultant force coefficients CL and Cf relate...Based on model tests, the lift and resultant forces on small square cylinders caused by waves (regular and irregular) and currents are analyzed in this paper. The lift and resultant force coefficients CL and Cf related to KC number and the effect of direction of wave propagation are also given, which may be useful for practical engineering application.展开更多
Wave diffraction of two concentric porous cylinders with varying porosity was studied by using an analytical method based on eigenfunction matching.The fluid domain around the cylinders is divided into three sub-domai...Wave diffraction of two concentric porous cylinders with varying porosity was studied by using an analytical method based on eigenfunction matching.The fluid domain around the cylinders is divided into three sub-domains and in each sub-domain an eigenfunction expansion of the velocity potential is obtained by satisfying the Laplace equation,the boundary conditions on the free surface and on the sea bed.The unknown coefficients of eigenfunction expansions are determined by boundary conditions on the porous hulls.In the paper,the boundary conditions are based upon the assumption that the flow in the porous medium is governed by Darcy's law.Two porous-effect parameters applied on two porous cylinders are functions of the vertical coordinate instead of the constant.Wave loading on the outer and inner cylinder is presented in the numerical results.展开更多
The fatigue damage caused by flow-induced vibration(FIV)is one of the major concerns for multiple cylindrical structures in many engineering applications.The FIV suppression is of great importance for the security of ...The fatigue damage caused by flow-induced vibration(FIV)is one of the major concerns for multiple cylindrical structures in many engineering applications.The FIV suppression is of great importance for the security of many cylindrical structures.Many active and passive control methods have been employed for the vibration suppression of an isolated cylinder undergoing vortex-induced vibrations(VIV).The FIV suppression methods are mainly extended to the multiple cylinders from the vibration control of the isolated cylinder.Due to the mutual interference between the multiple cylinders,the FIV mechanism is more complex than the VIV mechanism,which makes a great challenge for the FIV suppression.Some efforts have been devoted to vibration suppression of multiple cylinder systems undergoing FIV over the past two decades.The control methods,such as helical strakes,splitter plates,control rods and flexible sheets,are not always effective,depending on many influence factors,such as the spacing ratio,the arrangement geometrical shape,the flow velocity and the parameters of the vibration control devices.The FIV response,hydrodynamic features and wake patterns of the multiple cylinders equipped with vibration control devices are reviewed and summarized.The FIV suppression efficiency of the vibration control methods are analyzed and compared considering different influence factors.Further research on the FIV suppression of multiple cylinders is suggested to provide insight for the development of FIV control methods and promote engineering applications of FIV control methods.展开更多
Cooling strength is one of the important factors affecting microstructure and properties of gas cylinders during quenching process,and reasonable water spray volume can effectively improve the quality of gas cylinders...Cooling strength is one of the important factors affecting microstructure and properties of gas cylinders during quenching process,and reasonable water spray volume can effectively improve the quality of gas cylinders and reduce production costs.To find the optimal water spray parameters,a fluid-solid coupling model with three-phase flow was established in consideration of water-vapor conversion.The inner and outer walls of gas cylinder with the dimensions of d914 mm×38 mm×12000 mm were quenched using multi-nozzle water spray system.The internal pressure,average heat transfer coefficient(have)and stress of the gas cylinder under different water spray volumes during quenching process were studied.Finally,the mathematical model was experimentally verified.The results show that both the internal pressure and have increase along with the increase of spray volume.The internal pressure increases slowly first and then rapidly,but have increases rapidly first and then slowly.To satisfy hardenability of gas cylinders,the minimum spray volume should not be less than 40 m^3/(h·m).The results of stress indicate that water spray quenching will not cause deformation of bottle body in the range of water volume from 40 to 290 m^3/(h·m).展开更多
The interaction of water waves with multiple circular cylinders is analysed briefly in this paper. The formula obtained by Linton and Evans is improved to introduce a relation of phase between cylinders. The condition...The interaction of water waves with multiple circular cylinders is analysed briefly in this paper. The formula obtained by Linton and Evans is improved to introduce a relation of phase between cylinders. The condition for the existence of the solution has been proved. The numerical results are compared with analytic solutions (Linton and Evans), numerical solutions and experimental data (Isaacson), and good agreement has been found.展开更多
A double cylinders type traveling wave ultrasonic motor using composite transducer was proposed.The proposed stator contained two cylinders and one composite transducer,and the transducer located on the outer surfaces...A double cylinders type traveling wave ultrasonic motor using composite transducer was proposed.The proposed stator contained two cylinders and one composite transducer,and the transducer located on the outer surfaces of cylinders.The composite transducer included two exponential horns located on leading ends,and the horns insected with the cylinders at tip ends.Two degenerated flexural vibration modes spatially and temporally orthogonal to each other were excited in each cylinder by the composite transducer.In this new design,a single transducer could excite two flexural traveling waves in the cylinders.Thus,elliptical motions were achieved at the particles on the teeth.The working principle of the proposed motor was analyzed.The cylinder and transducer were designed with FEM.The resonant frequencies of two vibration modals of the stator were tuned to be the same,and the motion trajectories of nodes on the teeth were analyzed.Transient analysis results show that the motion trajectories of teeth are ellipses.The results of this paper can guide the development of this new type of ultrasonic motor.展开更多
We suppose that in order to maintain high accuracy of holes and to lower residual stresses after cold expansion of thick-walled cylinders, which undergo cross-section plastic deformation, it is necessary to perform ax...We suppose that in order to maintain high accuracy of holes and to lower residual stresses after cold expansion of thick-walled cylinders, which undergo cross-section plastic deformation, it is necessary to perform axial plastic compression and subsequent cold expansion with small interferences. To test this hypothesis, we studied hoop, radial and axial residual stresses in cylinders made of carbon steel AISI 1050 with hole diameter of 5 mm, outer diameter of 15 mm and length of 30 mm by Sachs method as well as accuracy of expanded holes. It is found that double cold expansion with total interference equal to 5.1% generates hoop residual stresses with largest absolute value equal to 284 MPa and ensures high holes accuracy(IT7). After plastic compression with strain equal to 0.5 and 1% the mentioned stresses reduced to 120 and 75 MPa respectively,and accuracy of the holes reduced as well. Subsequent cold expansion with small interference equal to 0.9% helps to restore holes accuracy(IT7)gained by double cold expansion and ensure that absolute value of hoop residual stresses(177 MPa) is lower compared to double cold expansion.展开更多
This study focuses on the transitions in flow states around two-, three-and four-inline square cylinders under the effect of Reynolds numbers at two different gap spacing values using the lattice Boltzmann method. For...This study focuses on the transitions in flow states around two-, three-and four-inline square cylinders under the effect of Reynolds numbers at two different gap spacing values using the lattice Boltzmann method. For this purpose, Reynolds number is varied in the range 1–130 while two different values of spacing taken into account are gap spacing =2 and 5. Before going to actual problem, the code is tested for flow around a single square cylinder by comparing the results with experimental and numerical results of other researchers, and good agreement is found.The current numerical computations yield that for both spacing values and all combinations of cylinders there exist three different sates of flow depending on Reynolds numbers: steady state, transitional state and unsteady state. It is found that the range of Reynolds numbers for these flow states is different for both spacing values. At gap spacing =2 the range of Reynolds numbers for each flow state decreases by increasing the number of cylinders while at gap spacing =5 opposite trend is observed. The results also show that at gap spacing =2 the reduction in drag force is greater than the corresponding reduction at gap spacing =5. The maximum reduction in drag force is observed at Reynolds numbers =1 at both spacing values. Similarly, at both spacing values and all Reynolds numbers, the maximum reduction in drag force is observed for the case of four-inline square cylinders.展开更多
基金Supported by the National Natural Science Foundation of China(52201350,52201394,and 52271301)the Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(Grant No.SML2022008).
文摘To explore the relationship between dynamic characteristics and wake patterns,numerical simulations were conducted on three equal-diameter cylinders arranged in an equilateral triangle.The simulations varied reduced velocities and gap spacing to observe flow-induced vibrations(FIVs).The immersed boundary–lattice Boltzmann flux solver(IB–LBFS)was applied as a numerical solution method,allowing for straightforward application on a simple Cartesian mesh.The accuracy and rationality of this method have been verified through comparisons with previous numerical results,including studies on flow past three stationary circular cylinders arranged in a similar pattern and vortex-induced vibrations of a single cylinder across different reduced velocities.When examining the FIVs of three cylinders,numerical simulations were carried out across a range of reduced velocities(3.0≤Ur≤13.0)and gap spacing(L=3D,4D,and 5D).The observed vibration response included several regimes:the desynchronization regime,the initial branch,and the lower branch.Notably,the transverse amplitude peaked,and a double vortex street formed in the wake when the reduced velocity reached the lower branch.This arrangement of three cylinders proved advantageous for energy capture as the upstream cylinder’s vibration response mirrored that of an isolated cylinder,while the response of each downstream cylinder was significantly enhanced.Compared to a single cylinder,the vibration and flow characteristics of this system are markedly more complex.The maximum transverse amplitudes of the downstream cylinders are nearly identical and exceed those observed in a single-cylinder set-up.Depending on the gap spacing,the flow pattern varied:it was in-phase for L=3D,antiphase for L=4D,and exhibited vortex shedding for L=5D.The wake configuration mainly featured double vortex streets for L=3D and evolved into two pairs of double vortex streets for L=5D.Consequently,it well illustrates the coupling mechanism that dynamics characteristics and wake vortex change with gap spacing and reduced velocities.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12372251 and 12132015).
文摘The lattice Boltzmann method(LBM)is employed to simulate flow around two staggered cylinders within a confined channel.The numerical model is validated against existing experimental data by comparing drag coefficients and Strouhal numbers in the single-cylinder configuration.The study systematically investigates the influence of vertical(h)and horizontal(l)spacing between the cylinders,as well as the Reynolds number(Re=0.1–160),on the hydrodynamic forces,streamline patterns,and vortex dynamics.Results indicate that reducing the horizontal spacing l suppresses flow separation behind the upstream cylinder,while either excessively small or large vertical spacing h diminishes separation in the downstream cylinder.The onset of periodic vortex shedding is delayed due to inter-cylinder interactions,with the critical Reynolds number increasing to Rec=71–112,significantly higher than that of a single-cylinder case(Re_(c)≈69).During the vortex shedding regime,the downstream cylinder exhibits a greater lift force fluctuation compared to the upstream cylinder.At Re=160,the root-mean-square lift coefficient(C′_(L))ranges from approximately 0.17 to 0.56 for the downstream cylinder,and from 0.018 to 0.4 for the upstream one.The shedding frequency,characterized by the Strouhal number(St),increases with Reynolds number,reaching St=0.12–0.18 at Re=160.Variations in h and l significantly influence St,with a decrease in l or an increase in h lowering the shedding frequency—this effect is more pronounced in the horizontal direction.
基金supported by the National Natural Science Foundation of China(No.52222503)the Natural Science Foundation of Zhejiang Province(No.LD22E050003),China.
文摘The integrated valve-controlled cylinder combines various control and execution components in hydraulic transmission systems.Its precise control and rapid response characteristics make it widely used in mobile equipment for aerospace,robotics,and other engineering applications.Additive manufacturing provides high design freedom which can further enhance the power density of integrated valve-controlled cylinders.However,there is a lack of effective design methods to guide the additive manufacturing of valve-controlled cylinders for more efficient hydraulic energy transmission.This study accordingly introduces an energy-saving design method based on additive manufacturing for integrated valve-controlled cylinders.The method consists of two main parts:(1)redesigning the manifold block to eliminate leakage points and reduce energy losses through integrated design of the valve,cylinder,and piping;(2)establishing a pressure loss model to achieve energy savings through optimized flow channel design for bends with different parameters.Compared to traditional valve-controlled cylinders,the integrated valvecontrolled cylinder developed from our method reduces the weight by 31%,volume by 55%,and pressure loss in the main flow channel by over 30%.This indicates that the design achieves both lightweight construction and improved hydraulic transmission efficiency.This study provides theoretical guidance for the design of lightweight and energy-efficient valve-controlled cylinders,and may aid the design of similar hydraulic machinery.
文摘Flow characteristics around a wall-mounted square cylinder have been numerically simulated at aspect ratios (AR) ranging from 4 to 7 at Re =10 000. Four turbulence models have been compared in terms of drag coefficient (C_D). The closest result has been provided by two turbulence models, namely, k-ε Realizable and k ?ω Shear Stress Transport (SST). Hence, these models were utilized to present the flow patterns of pressure distributions, turbulent kinetic energy values, velocity magnitude values with streamlines, streamwise velocity components, crossstream velocity components and spanwise velocity components on different planes. Flow stagnation has been attained in front of the cylinder. Pressure values peaked for the upstream region. Over the cylinders, the tip vortex structure was dominant owing to the influence of the free end. Flow separation from the top front edge of the body has been obtained. The dividing streamline affected by the flow separation was highly effective in the wake region and moved nearer to the body when the aspect ratio was decreased;the reason was the wake shrinkage owing to the decreasing aspect ratio. Upwash and downwash have been seen in the cylinder wake. These two models presented similar flow patterns and drag coefficients. These drag coefficients are in good agreement with those in previous studies.
基金financially supported by the National Natural Science Foundation of China(22478286)。
文摘In this study,four types of spiral fins with varying parameters were mounted on an upstream cylinder,and the effects of spiral fins on the vibration response of heat exchange tubes and the vortex structure in cross flow were studied through experiments and numerical simulations.The results indicate a strong dependency of the cylinder's vibration response on the fin parameters.The results indicate that the vibration response and wake structure of the cylinder are significantly influenced by the parameters of the fins.The introduction of a finned cylinder affects both its own vibration amplitude and frequency,as well as the downstream cylinder.The amplitudes of finned cylinders Ⅰ and Ⅲ are reduced by 57.8% and 59.9%,respectively,compared to the bare cylinder.This reduction helps to restrain vibration and diminishes the amplitudes of the downstream cylinder.Although finned cylinder Ⅱ slightly decreases its own vibration,it increases the amplitude of the downstream cylinder by 13.7%.The mean drag coefficient and the root mean square of the lift coefficient of the finned cylinder are higher than those of the bare cylinder when the finned cylinder is positioned upstream.Smaller pitch and larger equivalent diameter will lead to increased drag,resulting in enhanced vortex shedding in the wake,which amplifies the vibrations of the cylinder in that wake.The downstream of finned cylinder Ⅱ has the widest wake and higher vortex strength,and the dynamic load and vibration of the downstream cylinder are increased.The vortex intensity decays faster in the wake of finned cylinder Ⅲ,and the vibration of the downstream cylinder is weaker.
文摘The analysis of the characteristics of the cushion process of the pneumatic cushion cylinder is presented, and the nonlinear model of pneumatic cushion cylinders is built in the form of nonlinear differential equations. Besides, through the simulation of the pressure in the cushion chamber, the characteristics of the pneumatic cushion cylinder are obtained, which helps to understand the performance of the pneumatic cushion cylinder and improve or design the better cushion structure.
文摘In this study, the laminar heat transfer and nanofluid flow between two porous horizontal concentric cylinders was investigated. The problem is investigated in two different geometries and the Re=10, 25, 50, 75, 100 and volume fraction 0, 0.2%, 0.5%, 2% and 5% that related to copper nanoparticles, and porous medium porosity of 0.5 and 0.9. Compared to the first geometry, the convective coefficient in the second geometry increases by 8.3%, 7% and 5.5% at Reynolds numbers of 100, 75 and 50, respectively. Comparison of the outlet temperatures for two heat fluxes of 300 and 1200 W/m^2 indicates a 2.5% temperature growth by a fourfold increase in the heat fluxes. Also, the higher Nusselt number is associated with the second geometry occurring at porosities of 0.9 and 0.5, respectively. In both geometries, the Nusselt number values at the porosity of 0.9 are higher, which is due to the increased nanofluid convection at higher porosities. The velocity of the nanofluid experiences a two-fold increase at the outlet compared to its inlet velocity in the first geometry and for both porosities. Similarly, a three-fold increase was achieved in the second geometry and for both porosities.
基金supported by the National Basic Research Program of China (2009CB724104)the National Natural Science Foundation of China (90716010)
文摘The Xu ＆ Yan scale-adaptive simulation （XYSAS） model is employed to simulate the flows past wavy cylinders at Reynolds number 8 × 10 3.This approach yields results in good agreement with experimental measurements.The mean flow field and near wake vortex structure are replicated and compared with that of a corresponding circular cylinder.The effects of wavelength ratios λ/D m from 3 to 7,together with the amplitude ratios a /D m of 0.091 and 0.25,are fully investigated.Owing to the wavy configuration,a maximum reduction of Strouhal number and root-meansquare （r.m.s） fluctuating lift coefficients are up to 50% and 92%,respectively,which means the vortex induced vibration （VIV） could be effectively alleviated at certain larger values of λ/D m and a /D m.Also,the drag coefficients can be reduced by 30%.It is found that the flow field presents contrary patterns with the increase of λ/D m.The free shear layer becomes much more stable and rolls up into mature vortex only further downstream when λ/D m falls in the range of 5-7.The amplitude ratio a /D m greatly changes the separation line,and subsequently influences the wake structures.
基金financially supported by Joint Key Funds of Zhejiang Provincial Natural Science Foundation of China and Powerchina Huadong Engineering Corporation Limited(Grant No.LHZ19E090004)the National Key R&D Program of China(Grant No.2018YFD0900901)
文摘A series of three-dimensional numerical simulations is carried out to investigate the effect of inclined angle on flow behavior behind two side-by-side inclined cylinders at low Reynolds number Re=100 and small spacing ratio T/D=1.5 (T is the center-to-center distance between two side-by-side cylinders, D is the diameter of cylinder). The instantaneous and time-averaged flow fields, force coefficients and Strouhal numbers are analyzed. Special attention is focused on the axial flow characteristics with variation of the inclined angle. The results show that the inclined angle has a significant effect on the gap flow behaviors behind two inclined cylinders. The vortex shedding behind two cylinders is suppressed with the increase of the inclined angle as well as the flip-flop gap flow. Moreover, the mean drag coefficient, root-mean-square lift coefficient and Strouhal numbers decrease monotonously with the increase of the inclined angle, which follows the independent principle at small inclined angles.
基金supported by the Zhejiang Provincial Natural Science Foundation of China under Grant No. LY14E090009State Key Laboratory of Satellite Ocean Environment Dynamics (Second Institute of Oceanography, SOA), State Key Laboratory of Fluid Power Transmission and Control (GZKF-201310)+1 种基金State Key Laboratory of Ocean Engineering, China. The National Research Foundation of Singapore (NRF-CRP5-2009-01)Maritime Research Centre and Nanyang Environment and Water Research Institute, Nanyang Technological University, Singapore, is acknowledged
文摘In this paper, flow around two circular cylinders in tandem arrangement with unequal diameters has been investigated using the particle image velocimetry technique(PIV) in a water channel. The upstream to downstream diameter ratio was kept constant at d/D = 2/3, the centre-to-centre distance was varied from 1.2D to 5D and the Reynolds number was varied from 1200 to 4800. The flow characteristics were analyzed through ensemble-averaged patterns of velocity, vorticity, normalized Reynolds stress contours and streamlines. Based on ensemble-averaged and instantaneous flow fields, different flow patterns, including single-wakeshedding at small spacing ratio, bi-stable flow behavior(alternating behavior of reattachment and vortex shedding) at intermediate spacing ratio and co-shedding pattern at large spacing ratio were observed. The effects of Reynolds number and the centre-to-centre spacing ratio on flow patterns and turbulent characteristics were also investigated. It was found that the diameter ratio appears to have a certain effect on the flow patterns at intermediate spacing ratios, where the reattachment of shear layer depends on the lateral width of the wake flow in the lee of the upstream cylinder. Extensive discussion on the distributions of Reynolds stress and turbulent kinetic energy was presented.
基金supported by the National Natural Science Foundation of China(Grant No.40871050)
文摘The flow past two tandem circular cylinders of different diameters was simulated using the finite volume method. The diameter of the downstream main cylinder （D） was kept constant, and the diameter of the upstream control cylinder （d） varied from 0.1D to D. The studied Reynolds numbers based on the diameter of the downstream main cylinder were 100 and 150. The gap between the control cylinder and the main cylinder （G） ranged from 0.1D to 4D. It is concluded that the gap-to-diameter ratio （G/D） and the diameter ratio between the two cylinders （d/D） have important effects on the drag and lift coefficients, pressure distributions around the cylinders, vortex shedding frequencies from the two cylinders, and flow characteristics.
基金supported by the Fundamental Research Funds for the Central Universities and NPRP 08-691-2-289 grant from Qatar National Research Fund (QNRF)
文摘The finite element method （FEM） is employed to analyze the resonant oscillations of the liquid confined within multiple or an array of floating bodies with fully nonlinear boundary conditions on the free surface and the body surface in two dimensions. The velocity potentials at each time step are obtained through the FEM with 8-node quadratic shape functions. The finite element linear system is solved by the conjugate gradient （CG） method with a symmetric successive overelaxlation （SSOR） preconditioner. The waves at the open boundary are absorbed by the combination of the damping zone method and the Sommerfeld-Orlanski equation. Numerical examples are given by an array of floating wedge- shaped cylinders and rectangular cylinders. Results are provided for heave motions including wave elevations, profiles and hydrodynamic forces. Comparisons are made in several cases with the results obtained from the second order solution in the time domain. It is found that the wave amplitude in the middle region of the array is larger than those in other places, and the hydrodynamic force on a cylinder increases with the cylinder closing to the middle of the array.
文摘Based on model tests, the lift and resultant forces on small square cylinders caused by waves (regular and irregular) and currents are analyzed in this paper. The lift and resultant force coefficients CL and Cf related to KC number and the effect of direction of wave propagation are also given, which may be useful for practical engineering application.
基金Supported by the National Natural Science Foundation of China under Grant No.51079032
文摘Wave diffraction of two concentric porous cylinders with varying porosity was studied by using an analytical method based on eigenfunction matching.The fluid domain around the cylinders is divided into three sub-domains and in each sub-domain an eigenfunction expansion of the velocity potential is obtained by satisfying the Laplace equation,the boundary conditions on the free surface and on the sea bed.The unknown coefficients of eigenfunction expansions are determined by boundary conditions on the porous hulls.In the paper,the boundary conditions are based upon the assumption that the flow in the porous medium is governed by Darcy's law.Two porous-effect parameters applied on two porous cylinders are functions of the vertical coordinate instead of the constant.Wave loading on the outer and inner cylinder is presented in the numerical results.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.U2106223,51979193,52301352)。
文摘The fatigue damage caused by flow-induced vibration(FIV)is one of the major concerns for multiple cylindrical structures in many engineering applications.The FIV suppression is of great importance for the security of many cylindrical structures.Many active and passive control methods have been employed for the vibration suppression of an isolated cylinder undergoing vortex-induced vibrations(VIV).The FIV suppression methods are mainly extended to the multiple cylinders from the vibration control of the isolated cylinder.Due to the mutual interference between the multiple cylinders,the FIV mechanism is more complex than the VIV mechanism,which makes a great challenge for the FIV suppression.Some efforts have been devoted to vibration suppression of multiple cylinder systems undergoing FIV over the past two decades.The control methods,such as helical strakes,splitter plates,control rods and flexible sheets,are not always effective,depending on many influence factors,such as the spacing ratio,the arrangement geometrical shape,the flow velocity and the parameters of the vibration control devices.The FIV response,hydrodynamic features and wake patterns of the multiple cylinders equipped with vibration control devices are reviewed and summarized.The FIV suppression efficiency of the vibration control methods are analyzed and compared considering different influence factors.Further research on the FIV suppression of multiple cylinders is suggested to provide insight for the development of FIV control methods and promote engineering applications of FIV control methods.
基金Project(51674096)supported by the National Natural Science Foundation of ChinaProject(E2016203119)supported by Hebei Natural Science Foundation of ChinaProject(18211045)supported by the Key Research and Development Foundation in Hebei Province of China
文摘Cooling strength is one of the important factors affecting microstructure and properties of gas cylinders during quenching process,and reasonable water spray volume can effectively improve the quality of gas cylinders and reduce production costs.To find the optimal water spray parameters,a fluid-solid coupling model with three-phase flow was established in consideration of water-vapor conversion.The inner and outer walls of gas cylinder with the dimensions of d914 mm×38 mm×12000 mm were quenched using multi-nozzle water spray system.The internal pressure,average heat transfer coefficient(have)and stress of the gas cylinder under different water spray volumes during quenching process were studied.Finally,the mathematical model was experimentally verified.The results show that both the internal pressure and have increase along with the increase of spray volume.The internal pressure increases slowly first and then rapidly,but have increases rapidly first and then slowly.To satisfy hardenability of gas cylinders,the minimum spray volume should not be less than 40 m^3/(h·m).The results of stress indicate that water spray quenching will not cause deformation of bottle body in the range of water volume from 40 to 290 m^3/(h·m).
文摘The interaction of water waves with multiple circular cylinders is analysed briefly in this paper. The formula obtained by Linton and Evans is improved to introduce a relation of phase between cylinders. The condition for the existence of the solution has been proved. The numerical results are compared with analytic solutions (Linton and Evans), numerical solutions and experimental data (Isaacson), and good agreement has been found.
基金Sponsored by the National Natural Science Foundation of China (Grant No. 50875057 and 51075082)the State Key Laboratory of Robotics and Systems (HIT No. SKLRS200901A04)
文摘A double cylinders type traveling wave ultrasonic motor using composite transducer was proposed.The proposed stator contained two cylinders and one composite transducer,and the transducer located on the outer surfaces of cylinders.The composite transducer included two exponential horns located on leading ends,and the horns insected with the cylinders at tip ends.Two degenerated flexural vibration modes spatially and temporally orthogonal to each other were excited in each cylinder by the composite transducer.In this new design,a single transducer could excite two flexural traveling waves in the cylinders.Thus,elliptical motions were achieved at the particles on the teeth.The working principle of the proposed motor was analyzed.The cylinder and transducer were designed with FEM.The resonant frequencies of two vibration modals of the stator were tuned to be the same,and the motion trajectories of nodes on the teeth were analyzed.Transient analysis results show that the motion trajectories of teeth are ellipses.The results of this paper can guide the development of this new type of ultrasonic motor.
基金Lyudmila Petrova for invaluable metrological support. A.I.D. also thanks RFBR grant no. 15-08-01511a
文摘We suppose that in order to maintain high accuracy of holes and to lower residual stresses after cold expansion of thick-walled cylinders, which undergo cross-section plastic deformation, it is necessary to perform axial plastic compression and subsequent cold expansion with small interferences. To test this hypothesis, we studied hoop, radial and axial residual stresses in cylinders made of carbon steel AISI 1050 with hole diameter of 5 mm, outer diameter of 15 mm and length of 30 mm by Sachs method as well as accuracy of expanded holes. It is found that double cold expansion with total interference equal to 5.1% generates hoop residual stresses with largest absolute value equal to 284 MPa and ensures high holes accuracy(IT7). After plastic compression with strain equal to 0.5 and 1% the mentioned stresses reduced to 120 and 75 MPa respectively,and accuracy of the holes reduced as well. Subsequent cold expansion with small interference equal to 0.9% helps to restore holes accuracy(IT7)gained by double cold expansion and ensure that absolute value of hoop residual stresses(177 MPa) is lower compared to double cold expansion.
文摘This study focuses on the transitions in flow states around two-, three-and four-inline square cylinders under the effect of Reynolds numbers at two different gap spacing values using the lattice Boltzmann method. For this purpose, Reynolds number is varied in the range 1–130 while two different values of spacing taken into account are gap spacing =2 and 5. Before going to actual problem, the code is tested for flow around a single square cylinder by comparing the results with experimental and numerical results of other researchers, and good agreement is found.The current numerical computations yield that for both spacing values and all combinations of cylinders there exist three different sates of flow depending on Reynolds numbers: steady state, transitional state and unsteady state. It is found that the range of Reynolds numbers for these flow states is different for both spacing values. At gap spacing =2 the range of Reynolds numbers for each flow state decreases by increasing the number of cylinders while at gap spacing =5 opposite trend is observed. The results also show that at gap spacing =2 the reduction in drag force is greater than the corresponding reduction at gap spacing =5. The maximum reduction in drag force is observed at Reynolds numbers =1 at both spacing values. Similarly, at both spacing values and all Reynolds numbers, the maximum reduction in drag force is observed for the case of four-inline square cylinders.
