Based on the extended Huygens-Fresnel principle, we study the propagation properties of stochastic electromagnetic double-vortex beams in a turbulent atmosphere. The result shows that the spreading of partially cohere...Based on the extended Huygens-Fresnel principle, we study the propagation properties of stochastic electromagnetic double-vortex beams in a turbulent atmosphere. The result shows that the spreading of partially coherent double-vortex beams can be smaller than that of fully coherent ones. The degree of polarization of this kind of beam will experience change, which is dependent on the degree of polarization of the source plane, the atmospheric turbulence, topological charge, and the spatial coherence. The results may have applications in space optical communication.展开更多
Compression and stretching of ring-vortex solitons, which is a novel self-similar solution of（2＋1）-dimensional diffraction decreasing waveguide, is investigated analytically and numerically. We obtain the ring-vort...Compression and stretching of ring-vortex solitons, which is a novel self-similar solution of（2＋1）-dimensional diffraction decreasing waveguide, is investigated analytically and numerically. We obtain the ring-vortex solitons via the similarity transformation method. The distance modulation for the width, the diffraction, and the nonlinear response, strongly affects the form and the behavior of the self-similar vortex, and facilitates the efficient compression of optical waves. This approximate ring-vortex solitons can reflect the real properties of self-similar optical vortex beams during propagation under certain parameter window selection. Specific examples and figures are given to illustrate discussed features. The results obtained in this paper may have potential values for all-optical data-processing schemes and the design of beam compressors and amplifiers.展开更多
In the current study, the effects of a combined application between micro-vortex generator and boundary layer suction on the flow characteristics of a high-load compressor cascade are investigated. The micro-vortex ge...In the current study, the effects of a combined application between micro-vortex generator and boundary layer suction on the flow characteristics of a high-load compressor cascade are investigated. The micro-vortex generator with a special configuration and the longitudinal suction slot are adopted. The calculated results show that a reverse flow region, which is considered the main reason for occurring stall at 7.9° incidence, grows and collapses rapidly near the leading edge and leads to two critical points occurring on the end-wall with the increasing incidence in the baseline. As the micro-vortex generator is introduced in the baseline cascade, the corner separation is switched to a trailing edge separation by the thrust from the induced vortex. Meanwhile, the occurrence of failure is delayed due to the mixed low energy fluid and main flow. The synergistic effects between the micro-vortex generator and the boundary layer suction on the performance of the cascade are superior to the baseline at all the incidence conditions before the occurrence of failure, and the sudden deterioration of the cascade occurs at 10.3° incidence. The optimal results show that the farther upstream suction position, the lower total pressure loss of the cascade with vortex generator at the near stall condition. Moreover, the induced vortex with a leg can migrate the accumulated low energy fluid backward to delay the occurrence of stall.展开更多
For purpose of easy identification of the role of free vortices on the lift and drag and for purpose of fast or engineering evaluation of forces for each individual body, we will extend in this paper the Kutta-Joukows...For purpose of easy identification of the role of free vortices on the lift and drag and for purpose of fast or engineering evaluation of forces for each individual body, we will extend in this paper the Kutta-Joukowski （K J） theorem to the case of inviscid flow with multiple free vortices and multiple airfoils. The major simplification used in this paper is that each airfoil is represented by a lumped vortex, which may hold true when the distances between vortices and bodies are large enough. It is found that the Kutta-Joukowski theorem still holds provided that the local freestream velocity and the circulation of the bound vortex are modified by the induced velocity due to the out- side vortices and airfoils. We will demonstrate how to use the present result to identify the role of vortices on the forces according to their position, strength and rotation direction. Moreover, we will apply the present results to a two-cylinder example of Crowdy and the Wagner example to demon- strate how to perform fast force approximation for multi-body and multi-vortex problems. The lumped vortex assumption has the advantage of giving such kinds of approximate results which are very easy to use. The lack of accuracy for such a fast evaluation will be compensated by a rig- orous extension, with the lumped vortex assumption removed and with vortex production included, in a forthcoming paper.展开更多
By using a special momentum approach and with the help of interchange between singularity velocity and induced flow velocity, we derive in a physical way explicit force formulas for twodimensional inviscid flow involv...By using a special momentum approach and with the help of interchange between singularity velocity and induced flow velocity, we derive in a physical way explicit force formulas for twodimensional inviscid flow involving multiple bound and free vortices, multiple airfoils, and vortex production. These force formulas hold individually for each airfoil thus allowing for force decomposition, and the contributions to forces from singularities（such as bound and image vortices,sources, and doublets） and bodies out of an airfoil are related to their induced velocities at the locations of singularities inside this airfoil. The force contribution due to vortex production is related to the vortex production rate and the distance between each pair of vortices in production, thus frameindependent. The formulas are validated against a number of standard problems. These force formulas, which generalize the classic Kutta–Joukowski theorem（for a single bound vortex） and the recent generalized Lagally theorem（for problems without a bound vortex and vortex production） to more general cases, can be used to identify or understand the roles of outside vortices and bodies on the forces of the actual body, optimize arrangement of outside vortices and bodies for force enhancement or reduction, and derive analytical force formulas once the flow field is given or known.展开更多
In the present paper, flow configurations of cavitating flow around a straight NACA0009 foil with a gap between the foil tip and sidewall are investigated numerically by large eddy simulation（LES） coupled with Zwart...In the present paper, flow configurations of cavitating flow around a straight NACA0009 foil with a gap between the foil tip and sidewall are investigated numerically by large eddy simulation（LES） coupled with Zwart-Gerber-Belamri（ZGB） cavitation model. A Cartesian cut-cell method is used for mesh generation, which is of good orthogonality and high quality. A good agreement is obtained between simulation and experiment. Two influencing factors on vorticity distributions, the interaction between different vortices and the occurrence of cavitation, are discussed in detail based on the numerical results. A series of ？-shaped loops are observed during the development of the induced vortex, which is a result of the instability of vortex pair. This finding may provide a new viewpoint to control the evolution of tip-leakage vortex（TLV） cavitation. Moreover, it is found that the dilatation term plays a much more important role in the evolution of TLV cavitation compared with that in sheet cavitation.展开更多
In this paper, the self-organization process of the initially scattered 12 meso-β and -γ scale vortices evolving into a synoptic-scale typhoon-like vortex in the context of advection dynamics is numerically explored...In this paper, the self-organization process of the initially scattered 12 meso-β and -γ scale vortices evolving into a synoptic-scale typhoon-like vortex in the context of advection dynamics is numerically explored with an ）f-plane 2-D quasi-geostrophic vorticity equation model. The results show that the self-organization process was a step-by-step merging course, namely the two adjacent vortices first merged, then formed a tri-vortex flow pattern, and finally evolved into a resultant vortex of meso-α scale. Thus it can be seen as an interaction of binary vortices self-organization. Each initial vortex or vorticity lump confronted two ways out： it merged with an adjacent vortex, and thus became a source of the inner region vorticity of the new formed vortex; or it was stretched by the circulation of an adjacent vortex, and then became the vorticity source of the spiral band of new vortex. Similarly, each new formed vortex also confronted the two ways out, until the multi-vortex self-organized into a single vortex of lager scale. The representation precision of the initial vortex structure directly affected the speeds of the mutual rotation and merging of the resultant vortex. Therefore, it is important to provide an accurate description of initial vortex profiles. Finally, a property of the numerical solution of the self-organization for the 2-D quasi-geostrophic flow is that the total kinetic energy decays slowly, the total enstrophy decreases rapidly, and the circulation of the largest scale vortex grows quickly.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60977068 and 61178015)the Natural Science Foundation of Sanming University,China (Grant No. B201103/G)
文摘Based on the extended Huygens-Fresnel principle, we study the propagation properties of stochastic electromagnetic double-vortex beams in a turbulent atmosphere. The result shows that the spreading of partially coherent double-vortex beams can be smaller than that of fully coherent ones. The degree of polarization of this kind of beam will experience change, which is dependent on the degree of polarization of the source plane, the atmospheric turbulence, topological charge, and the spatial coherence. The results may have applications in space optical communication.
文摘Compression and stretching of ring-vortex solitons, which is a novel self-similar solution of（2＋1）-dimensional diffraction decreasing waveguide, is investigated analytically and numerically. We obtain the ring-vortex solitons via the similarity transformation method. The distance modulation for the width, the diffraction, and the nonlinear response, strongly affects the form and the behavior of the self-similar vortex, and facilitates the efficient compression of optical waves. This approximate ring-vortex solitons can reflect the real properties of self-similar optical vortex beams during propagation under certain parameter window selection. Specific examples and figures are given to illustrate discussed features. The results obtained in this paper may have potential values for all-optical data-processing schemes and the design of beam compressors and amplifiers.
基金co-supported by the National Natural Science Foundation of China(Grants Nos.51576162 and 51536006)
文摘In the current study, the effects of a combined application between micro-vortex generator and boundary layer suction on the flow characteristics of a high-load compressor cascade are investigated. The micro-vortex generator with a special configuration and the longitudinal suction slot are adopted. The calculated results show that a reverse flow region, which is considered the main reason for occurring stall at 7.9° incidence, grows and collapses rapidly near the leading edge and leads to two critical points occurring on the end-wall with the increasing incidence in the baseline. As the micro-vortex generator is introduced in the baseline cascade, the corner separation is switched to a trailing edge separation by the thrust from the induced vortex. Meanwhile, the occurrence of failure is delayed due to the mixed low energy fluid and main flow. The synergistic effects between the micro-vortex generator and the boundary layer suction on the performance of the cascade are superior to the baseline at all the incidence conditions before the occurrence of failure, and the sudden deterioration of the cascade occurs at 10.3° incidence. The optimal results show that the farther upstream suction position, the lower total pressure loss of the cascade with vortex generator at the near stall condition. Moreover, the induced vortex with a leg can migrate the accumulated low energy fluid backward to delay the occurrence of stall.
基金supported by National Basic Research Program of China (2012CB720205)
文摘For purpose of easy identification of the role of free vortices on the lift and drag and for purpose of fast or engineering evaluation of forces for each individual body, we will extend in this paper the Kutta-Joukowski （K J） theorem to the case of inviscid flow with multiple free vortices and multiple airfoils. The major simplification used in this paper is that each airfoil is represented by a lumped vortex, which may hold true when the distances between vortices and bodies are large enough. It is found that the Kutta-Joukowski theorem still holds provided that the local freestream velocity and the circulation of the bound vortex are modified by the induced velocity due to the out- side vortices and airfoils. We will demonstrate how to use the present result to identify the role of vortices on the forces according to their position, strength and rotation direction. Moreover, we will apply the present results to a two-cylinder example of Crowdy and the Wagner example to demon- strate how to perform fast force approximation for multi-body and multi-vortex problems. The lumped vortex assumption has the advantage of giving such kinds of approximate results which are very easy to use. The lack of accuracy for such a fast evaluation will be compensated by a rig- orous extension, with the lumped vortex assumption removed and with vortex production included, in a forthcoming paper.
基金supported by the National Basic Research Program of China (No. 2012CB720205)partly by the Natural National Science Foundation of China (No. 11472157)
文摘By using a special momentum approach and with the help of interchange between singularity velocity and induced flow velocity, we derive in a physical way explicit force formulas for twodimensional inviscid flow involving multiple bound and free vortices, multiple airfoils, and vortex production. These force formulas hold individually for each airfoil thus allowing for force decomposition, and the contributions to forces from singularities（such as bound and image vortices,sources, and doublets） and bodies out of an airfoil are related to their induced velocities at the locations of singularities inside this airfoil. The force contribution due to vortex production is related to the vortex production rate and the distance between each pair of vortices in production, thus frameindependent. The formulas are validated against a number of standard problems. These force formulas, which generalize the classic Kutta–Joukowski theorem（for a single bound vortex） and the recent generalized Lagally theorem（for problems without a bound vortex and vortex production） to more general cases, can be used to identify or understand the roles of outside vortices and bodies on the forces of the actual body, optimize arrangement of outside vortices and bodies for force enhancement or reduction, and derive analytical force formulas once the flow field is given or known.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51576143,11772239 and 91752105)the Science and Technology on Water Jet Propulsion Laboratory(Grant No.61422230101162223002)
文摘In the present paper, flow configurations of cavitating flow around a straight NACA0009 foil with a gap between the foil tip and sidewall are investigated numerically by large eddy simulation（LES） coupled with Zwart-Gerber-Belamri（ZGB） cavitation model. A Cartesian cut-cell method is used for mesh generation, which is of good orthogonality and high quality. A good agreement is obtained between simulation and experiment. Two influencing factors on vorticity distributions, the interaction between different vortices and the occurrence of cavitation, are discussed in detail based on the numerical results. A series of ？-shaped loops are observed during the development of the induced vortex, which is a result of the instability of vortex pair. This finding may provide a new viewpoint to control the evolution of tip-leakage vortex（TLV） cavitation. Moreover, it is found that the dilatation term plays a much more important role in the evolution of TLV cavitation compared with that in sheet cavitation.
基金Supported by the Key Project of National Natural Science Fbundation of China under Grant No. 40333028.
文摘In this paper, the self-organization process of the initially scattered 12 meso-β and -γ scale vortices evolving into a synoptic-scale typhoon-like vortex in the context of advection dynamics is numerically explored with an ）f-plane 2-D quasi-geostrophic vorticity equation model. The results show that the self-organization process was a step-by-step merging course, namely the two adjacent vortices first merged, then formed a tri-vortex flow pattern, and finally evolved into a resultant vortex of meso-α scale. Thus it can be seen as an interaction of binary vortices self-organization. Each initial vortex or vorticity lump confronted two ways out： it merged with an adjacent vortex, and thus became a source of the inner region vorticity of the new formed vortex; or it was stretched by the circulation of an adjacent vortex, and then became the vorticity source of the spiral band of new vortex. Similarly, each new formed vortex also confronted the two ways out, until the multi-vortex self-organized into a single vortex of lager scale. The representation precision of the initial vortex structure directly affected the speeds of the mutual rotation and merging of the resultant vortex. Therefore, it is important to provide an accurate description of initial vortex profiles. Finally, a property of the numerical solution of the self-organization for the 2-D quasi-geostrophic flow is that the total kinetic energy decays slowly, the total enstrophy decreases rapidly, and the circulation of the largest scale vortex grows quickly.
