The Stereo Particle Image Velocimetry(SPIV)technology is applied to measure the wingtip vortices generated by the up-down symmetrical split winglet.Then,the temporal biglobal Linear Stability Analysis(bi-global LSA)is...The Stereo Particle Image Velocimetry(SPIV)technology is applied to measure the wingtip vortices generated by the up-down symmetrical split winglet.Then,the temporal biglobal Linear Stability Analysis(bi-global LSA)is performed on this nearly equal-strength corotating vortex pair,which is composed of an upper vortex(vortex-u)and a down vortex(vortex-d).The results show that the instability eigenvalue spectrum illustrated by(ωr,ω_(i))contains two types of branches:discrete branch and continuous branch.The discrete branch contains the primary branches of vortex-u and vortex-d,the secondary branch of vortex-d and coupled branch,of which all of the eigenvalues are located in the unstable half-plane ofω_(i)>0,indicating that the wingtip vortex pair is temporally unstable.By contrast,the eigenvalues of the continuous branch are concentrated on the half-plane ofω_(i)<0 and the perturbation modes correspond to the freestream perturbation.In the primary branches of vortex-u and vortex-d,Mode P_(u) and Mode Pd are the primary perturbation modes,which exhibit the structures enclosed with azimuthal wavenumber m and radial wavenumber n,respectively.Besides,the results of stability curves for vortex-u and vortex-d demonstrate that the instability growth rates of vortex-u are larger than those of vortex-d,and the perturbation energy of Mode P_(u) is also larger than that of Mode Pd.Moreover,the perturbation energy of Mode P_(u) is up to 0.02650 and accounts for 33.56%percent in the corresponding branch,thereby indicating that the instability development of wingtip vortex is dominated by Mode P_(u).By further investigating the topological structures of Mode P_(u) and Mode Pd with streamwise wavenumbers,the most unstable perturbation mode with a large azimuthal wavenumber of m=5-6 is identified,which imposes on the entire core region of vortex-u.This large azimuthal wavenumber perturbation mode can suggest the potential physical-based flow control strategy by manipulating it.展开更多
The present paper describes control of wingtip vortices generated by vertical type wind turbine. The wind turbine consists of three circular cylinders. Each cylinder rotates on its own vertical axis and moves in orbit...The present paper describes control of wingtip vortices generated by vertical type wind turbine. The wind turbine consists of three circular cylinders. Each cylinder rotates on its own vertical axis and moves in orbit. It is known that wingtip vortices give rise to decrease of power generation performance as well as aerodynamic noise. Therefore, the goal of the study is to control wingtip vortices and to improve power generation performance. Numerical study was conducted for 14 models to find out control factors to suppress wingtip vortices. Numerical simulation visualized wingtips by streamlines as well as pressure distribution on the circular cylinder for evaluating Magnus effect. As a result, the following findings were obtained: 1) Installation of fully covered protection plates at both ends of the circular cylinder blades is greatly effective to suppress the wingtip vortices. 2) Curved wings attached to each cylinder are more effective to enhance power generation efficiency than flat ones, due to great increase in Magnus effect caused by large pressure difference on both sides of the curved wing. The power efficiency of the optimized model was improved up to 2.8%, which means 11 times that of the original model.展开更多
基金co-supported by the National Basic Research Program of China(No.2014CB744802)Major Research of National Natural Science Foundation of China(No.91952302)China Postdoctoral Science Foundation(No.2018 M642007)。
文摘The Stereo Particle Image Velocimetry(SPIV)technology is applied to measure the wingtip vortices generated by the up-down symmetrical split winglet.Then,the temporal biglobal Linear Stability Analysis(bi-global LSA)is performed on this nearly equal-strength corotating vortex pair,which is composed of an upper vortex(vortex-u)and a down vortex(vortex-d).The results show that the instability eigenvalue spectrum illustrated by(ωr,ω_(i))contains two types of branches:discrete branch and continuous branch.The discrete branch contains the primary branches of vortex-u and vortex-d,the secondary branch of vortex-d and coupled branch,of which all of the eigenvalues are located in the unstable half-plane ofω_(i)>0,indicating that the wingtip vortex pair is temporally unstable.By contrast,the eigenvalues of the continuous branch are concentrated on the half-plane ofω_(i)<0 and the perturbation modes correspond to the freestream perturbation.In the primary branches of vortex-u and vortex-d,Mode P_(u) and Mode Pd are the primary perturbation modes,which exhibit the structures enclosed with azimuthal wavenumber m and radial wavenumber n,respectively.Besides,the results of stability curves for vortex-u and vortex-d demonstrate that the instability growth rates of vortex-u are larger than those of vortex-d,and the perturbation energy of Mode P_(u) is also larger than that of Mode Pd.Moreover,the perturbation energy of Mode P_(u) is up to 0.02650 and accounts for 33.56%percent in the corresponding branch,thereby indicating that the instability development of wingtip vortex is dominated by Mode P_(u).By further investigating the topological structures of Mode P_(u) and Mode Pd with streamwise wavenumbers,the most unstable perturbation mode with a large azimuthal wavenumber of m=5-6 is identified,which imposes on the entire core region of vortex-u.This large azimuthal wavenumber perturbation mode can suggest the potential physical-based flow control strategy by manipulating it.
文摘The present paper describes control of wingtip vortices generated by vertical type wind turbine. The wind turbine consists of three circular cylinders. Each cylinder rotates on its own vertical axis and moves in orbit. It is known that wingtip vortices give rise to decrease of power generation performance as well as aerodynamic noise. Therefore, the goal of the study is to control wingtip vortices and to improve power generation performance. Numerical study was conducted for 14 models to find out control factors to suppress wingtip vortices. Numerical simulation visualized wingtips by streamlines as well as pressure distribution on the circular cylinder for evaluating Magnus effect. As a result, the following findings were obtained: 1) Installation of fully covered protection plates at both ends of the circular cylinder blades is greatly effective to suppress the wingtip vortices. 2) Curved wings attached to each cylinder are more effective to enhance power generation efficiency than flat ones, due to great increase in Magnus effect caused by large pressure difference on both sides of the curved wing. The power efficiency of the optimized model was improved up to 2.8%, which means 11 times that of the original model.
