A formula for the Magnus force on a rotating and translating solid cylinder in a fluid is constructed for two different fluid models. In both cases the flow is steady and frictionless with no formation or shedding of ...A formula for the Magnus force on a rotating and translating solid cylinder in a fluid is constructed for two different fluid models. In both cases the flow is steady and frictionless with no formation or shedding of eddies behind the cylinder. However, model one is founded on the assumption of irrotationality whereas model two is not but rather makes explicit use of the centrifugal force acting on the curving streamlines above the cylinder. Model two’s Magnus force comes out to be 15% larger in magnitude which is probably more than that can be accounted for by approximations made within the models. Observations will be needed to help decide which model comes closer to the truth. In the force formula the following factors are multiplied together: constant, fluid density, translation speed, and rotation frequency. For model one constant = 2;for model two constant = 2.3.展开更多
Experimental and numerical methods were used to investigate the Magnus phenomena over a spinning projectile.The pressure force acting on the surface of a spinning projectile was measured for various cases by employing...Experimental and numerical methods were used to investigate the Magnus phenomena over a spinning projectile.The pressure force acting on the surface of a spinning projectile was measured for various cases by employing a relatively novel experimental technique.A set of miniature pressure sensors along with a data acquisition board,battery and storage memory were placed inside a spinning model and the surface pressure were obtained through a remotely controlled system.Circumferential pressures of the model for both rotational and static conditions were obtained at two different free stream Mach numbers of 0.4 and 0.8 and at different angles of attack.The results showed the ability of this new test method to measure the very small Magnus force via surface pressures over the projectile.The results provide a deep insight into the flow structure and illustrate changes in the cross-flow separation locations as a result of rotation.Similar results were obtained by the numerical simulations and were compared with the experimental data.展开更多
The Magnus Hall effect(MHE) is a new type of linear-response Hall effect, recently proposed to appear in two-dimensional(2D) nonmagnetic systems at zero magnetic field in the ballistic limit. The MHE arises from a sel...The Magnus Hall effect(MHE) is a new type of linear-response Hall effect, recently proposed to appear in two-dimensional(2D) nonmagnetic systems at zero magnetic field in the ballistic limit. The MHE arises from a self-rotating Bloch electron moving under a gradient-electrostatic potential, analogous to the Magnus effect in the macrocosm. Unfortunately, the MHE is usually accompanied by a trivial transverse signal, which hinders its experimental observation. We systematically investigate the material realization and experimental measurement of the MHE, based on symmetry analysis and first-principles calculations. It is found that both the out-ofplane mirror and in-plane two-fold symmetries can neutralize the trivial transverse signal to generate clean MHE signals. We choose two representative 2D materials, monolayer MoS_(2), and bilayer WTe_(2), to study the quantitative dependency of MHE signals on the direction of the electric field. The results are qualitatively consistent with the symmetry analysis, and suggest that an observable MHE signal requires giant Berry curvatures. Our results provide detailed guidance for the future experimental exploration of MHE.展开更多
Spiral Magnus is a unique wind turbine system that rotates with cylinders which have spiral-shaped fins coiled around them （instead of using the more common propeller-type blades）. In the present study, three models...Spiral Magnus is a unique wind turbine system that rotates with cylinders which have spiral-shaped fins coiled around them （instead of using the more common propeller-type blades）. In the present study, three models （cylinder with no fins, cylinder with straight fins and cylinder with spiral fins） were installed, and fluid force measurements were performed by a strain gauge force balance. A PIV （particle image velocimetry） system was used to better understand the flow fields around the cylinder. Considering the results of the experiment, it was confirmed that, the aerodynamic performance of the rotating cylinder can be improved by the fin. However, the straight fin makes the flow close to the cylinder surface ineffective. The rotary cylinder with the spiral fins was able to generate the greatest lift among three models, because the spiral fin effectively influences the vicinity of the cylinder surface.展开更多
The Magnus effect is well known phenomena for producing high lift values from spinning symmetrical geometries such as cylinders, spheres, or disks. But, the Magnus force may also be produced by treadmill motion of aer...The Magnus effect is well known phenomena for producing high lift values from spinning symmetrical geometries such as cylinders, spheres, or disks. But, the Magnus force may also be produced by treadmill motion of aerodynamic bodies. To accomplish this, the skin of aerodynamic bodies may circulate with a constant circumferential speed. Here, a novel wing with treadmill motion of skin is introduced which may generate lift at zero air speeds. The new wing may lead to micro aerial vehicle configurations for vertical take-off or landing. To prove the concept, the NACA0015 aerofoil section with circulating skin is computationally investigated. Two cases of stationary air and moving air are studied. It is observed that lift can be generated in stationary air although drag force is also high. For moving air, the lift and drag forces may be adopted between the incidence angles 20° to 25° where lift can posses high values and drag can remain moderate.展开更多
This paper presents numerical studies of the Magnus effect for a kinetic turbine on a horizontal axis.To focus on the Magnus blade,a single self-spinning cylindrical blade is assumed.An iterative direct-forcing immers...This paper presents numerical studies of the Magnus effect for a kinetic turbine on a horizontal axis.To focus on the Magnus blade,a single self-spinning cylindrical blade is assumed.An iterative direct-forcing immersed boundary method is employed within the Eulerian-Lagrangian framework due to its capability to treat complex and moving geometries.The Eulerian fluid domain is discretized using the finite volume method while the Magnus rotor is represented by a set of discrete points/markers.The aim of the numerical studies is to provide insights for the design process and predict aerodynamic performances under various operating conditions.Results for stationary and self-spinning cylinders in turbulent flows are found to be in good agreement with published data.By increasing the aspect ratio of the cylinder(simulated segment length over its diameter)from 3 to 10,a 30%drop in lift coefficient and a 22%increase in drag coefficient were observed,which is believed to be attributed to an enhancement of the three-dimensionality of the near-wake.For the Magnus rotor,key parameters such as dynamic forcing and frequency,distribution of pressure coefficient and torque have been produced for two cases with different structural designs and working conditions.With increase of the aspect ratio from 3 to 10,stable forces are observed from the root side of the blade and the torque coefficient increases from 0.68 to 2.1,which indicates a superior performance in terms of power extraction.展开更多
This study examines the vortex-induced vibrations(VIV)and hydrodynamic characteristics of a rotating circular cylinder with two degrees of freedom(2DOF).The effects of varying mass ratios(M^(*)),rotation rates(α)and ...This study examines the vortex-induced vibrations(VIV)and hydrodynamic characteristics of a rotating circular cylinder with two degrees of freedom(2DOF).The effects of varying mass ratios(M^(*)),rotation rates(α)and reduced velocities(U^(*))on the cylinder’s vibration responses,hydrodynamic properties and near-wake structures are explored.The results indicate that the cylinder rotation significantly suppresses vibrations in the cross-flow direction,with the inhibitory effect intensifying with the increasing rotation ratioα.Additionally,contrary to the non-rotating cylinder,in which f_(x)^(*)=2f^(*)y,the rotating cylinder shows congruence in vibration frequencies in both the X-and Y-directions.In the motion trajectory,with the non-rotating cylinder exhibiting an“8”pattern,the rotating cylinder traces a single closed-loop shape.The mass ratio notably influences the displacement amplitude,trajectory,and phase portrait.Higher mass ratios(M^(*)=6,8)suppress the growth of time-averaged displacements in both the X-and Y-directions and the incidence of“lock-in”phenomena in the Y direction.Particularly,as M^(*)=2,α=1.0,1.5,the displacement in the Y-direction is notably higher than that under other conditions.The higher mass ratio also modifies the motion trajectory of the cylinder,shifting it from a closed-loop droplet shape to a single closed loop,with the frequency ratio between lift force and cross-flow displacement transitioning from 3:1 to 1:1.Vortex structure analysis reveals patterns such as“2P”,“P+S”,and“2S”,with high mass ratios showing a U-shaped mode and an extended“2S”region in the wake structure.展开更多
文摘A formula for the Magnus force on a rotating and translating solid cylinder in a fluid is constructed for two different fluid models. In both cases the flow is steady and frictionless with no formation or shedding of eddies behind the cylinder. However, model one is founded on the assumption of irrotationality whereas model two is not but rather makes explicit use of the centrifugal force acting on the curving streamlines above the cylinder. Model two’s Magnus force comes out to be 15% larger in magnitude which is probably more than that can be accounted for by approximations made within the models. Observations will be needed to help decide which model comes closer to the truth. In the force formula the following factors are multiplied together: constant, fluid density, translation speed, and rotation frequency. For model one constant = 2;for model two constant = 2.3.
文摘Experimental and numerical methods were used to investigate the Magnus phenomena over a spinning projectile.The pressure force acting on the surface of a spinning projectile was measured for various cases by employing a relatively novel experimental technique.A set of miniature pressure sensors along with a data acquisition board,battery and storage memory were placed inside a spinning model and the surface pressure were obtained through a remotely controlled system.Circumferential pressures of the model for both rotational and static conditions were obtained at two different free stream Mach numbers of 0.4 and 0.8 and at different angles of attack.The results showed the ability of this new test method to measure the very small Magnus force via surface pressures over the projectile.The results provide a deep insight into the flow structure and illustrate changes in the cross-flow separation locations as a result of rotation.Similar results were obtained by the numerical simulations and were compared with the experimental data.
基金Supported by the National Basic Research Program of China (Grant No.2019YFA0308403)the National Natural Science Foundation of China (Grant Nos.11822407,11947212,11704348,and NSFC20SC07)+1 种基金the China Postdoctoral Science Foundation (Grant No.2018M640513)the Hong Kong Research Grants Council (Grant Nos.26302118,16305019,and N HKUST626/18)。
文摘The Magnus Hall effect(MHE) is a new type of linear-response Hall effect, recently proposed to appear in two-dimensional(2D) nonmagnetic systems at zero magnetic field in the ballistic limit. The MHE arises from a self-rotating Bloch electron moving under a gradient-electrostatic potential, analogous to the Magnus effect in the macrocosm. Unfortunately, the MHE is usually accompanied by a trivial transverse signal, which hinders its experimental observation. We systematically investigate the material realization and experimental measurement of the MHE, based on symmetry analysis and first-principles calculations. It is found that both the out-ofplane mirror and in-plane two-fold symmetries can neutralize the trivial transverse signal to generate clean MHE signals. We choose two representative 2D materials, monolayer MoS_(2), and bilayer WTe_(2), to study the quantitative dependency of MHE signals on the direction of the electric field. The results are qualitatively consistent with the symmetry analysis, and suggest that an observable MHE signal requires giant Berry curvatures. Our results provide detailed guidance for the future experimental exploration of MHE.
文摘Spiral Magnus is a unique wind turbine system that rotates with cylinders which have spiral-shaped fins coiled around them （instead of using the more common propeller-type blades）. In the present study, three models （cylinder with no fins, cylinder with straight fins and cylinder with spiral fins） were installed, and fluid force measurements were performed by a strain gauge force balance. A PIV （particle image velocimetry） system was used to better understand the flow fields around the cylinder. Considering the results of the experiment, it was confirmed that, the aerodynamic performance of the rotating cylinder can be improved by the fin. However, the straight fin makes the flow close to the cylinder surface ineffective. The rotary cylinder with the spiral fins was able to generate the greatest lift among three models, because the spiral fin effectively influences the vicinity of the cylinder surface.
文摘The Magnus effect is well known phenomena for producing high lift values from spinning symmetrical geometries such as cylinders, spheres, or disks. But, the Magnus force may also be produced by treadmill motion of aerodynamic bodies. To accomplish this, the skin of aerodynamic bodies may circulate with a constant circumferential speed. Here, a novel wing with treadmill motion of skin is introduced which may generate lift at zero air speeds. The new wing may lead to micro aerial vehicle configurations for vertical take-off or landing. To prove the concept, the NACA0015 aerofoil section with circulating skin is computationally investigated. Two cases of stationary air and moving air are studied. It is observed that lift can be generated in stationary air although drag force is also high. For moving air, the lift and drag forces may be adopted between the incidence angles 20° to 25° where lift can posses high values and drag can remain moderate.
文摘This paper presents numerical studies of the Magnus effect for a kinetic turbine on a horizontal axis.To focus on the Magnus blade,a single self-spinning cylindrical blade is assumed.An iterative direct-forcing immersed boundary method is employed within the Eulerian-Lagrangian framework due to its capability to treat complex and moving geometries.The Eulerian fluid domain is discretized using the finite volume method while the Magnus rotor is represented by a set of discrete points/markers.The aim of the numerical studies is to provide insights for the design process and predict aerodynamic performances under various operating conditions.Results for stationary and self-spinning cylinders in turbulent flows are found to be in good agreement with published data.By increasing the aspect ratio of the cylinder(simulated segment length over its diameter)from 3 to 10,a 30%drop in lift coefficient and a 22%increase in drag coefficient were observed,which is believed to be attributed to an enhancement of the three-dimensionality of the near-wake.For the Magnus rotor,key parameters such as dynamic forcing and frequency,distribution of pressure coefficient and torque have been produced for two cases with different structural designs and working conditions.With increase of the aspect ratio from 3 to 10,stable forces are observed from the root side of the blade and the torque coefficient increases from 0.68 to 2.1,which indicates a superior performance in terms of power extraction.
基金supported by the Natural Science Foundation of Chongqing(Grant No.CSTB2024NSCQMSX0463).
文摘This study examines the vortex-induced vibrations(VIV)and hydrodynamic characteristics of a rotating circular cylinder with two degrees of freedom(2DOF).The effects of varying mass ratios(M^(*)),rotation rates(α)and reduced velocities(U^(*))on the cylinder’s vibration responses,hydrodynamic properties and near-wake structures are explored.The results indicate that the cylinder rotation significantly suppresses vibrations in the cross-flow direction,with the inhibitory effect intensifying with the increasing rotation ratioα.Additionally,contrary to the non-rotating cylinder,in which f_(x)^(*)=2f^(*)y,the rotating cylinder shows congruence in vibration frequencies in both the X-and Y-directions.In the motion trajectory,with the non-rotating cylinder exhibiting an“8”pattern,the rotating cylinder traces a single closed-loop shape.The mass ratio notably influences the displacement amplitude,trajectory,and phase portrait.Higher mass ratios(M^(*)=6,8)suppress the growth of time-averaged displacements in both the X-and Y-directions and the incidence of“lock-in”phenomena in the Y direction.Particularly,as M^(*)=2,α=1.0,1.5,the displacement in the Y-direction is notably higher than that under other conditions.The higher mass ratio also modifies the motion trajectory of the cylinder,shifting it from a closed-loop droplet shape to a single closed loop,with the frequency ratio between lift force and cross-flow displacement transitioning from 3:1 to 1:1.Vortex structure analysis reveals patterns such as“2P”,“P+S”,and“2S”,with high mass ratios showing a U-shaped mode and an extended“2S”region in the wake structure.
