Morphology as well as kinematics is a critical determinant of performance in flapping flight.To understand the effects of the structural traits on aerodynamics of bioflyers,three rectangular wings with aspect ratios...Morphology as well as kinematics is a critical determinant of performance in flapping flight.To understand the effects of the structural traits on aerodynamics of bioflyers,three rectangular wings with aspect ratios（AR）of1,2,and 4 performing hovering-like sinusoidal kinematics at wingtip based Reynolds number of 5 300 are experimentally investigated.Flow structures on sectional cuts along the wing span are compared.Stronger K-H instability is found on the leading edge vortex of wings with higher aspect ratios.Vortex bursting only appears on the outer spanwise locations of high-aspect-ratio wings.The vortex bursting on high-aspect-ratio wings is perhaps one of the reasons why bio-flyers normally have low-aspect-ratio wings.Quantitative analysis exhibits larger dimensionless circulation of the leading edge vortex（LEV）over higher aspect ratio wings except when vortex bursting happens.The average dimensionless circulation of AR1 and AR2 along the span almost equals the dimensionless circulation at the 50%span.The flow structure and the circulation analysis show that the sinusoidal kinematics suppresses breakdown of the LEV compared with simplified flapping kinematics used in similar studies.The Reynolds number effect results on AR4 show that in the current Re range,the overall flow structure is not sensitive to Reynolds number.展开更多
A theoretical nonlinear aeroelastic response analysis for a flexible high-aspect ratio wing excited by harmonic gust load is presented along with a companion wind tunnel test. A multidisci- plinary coupled numerical c...A theoretical nonlinear aeroelastic response analysis for a flexible high-aspect ratio wing excited by harmonic gust load is presented along with a companion wind tunnel test. A multidisci- plinary coupled numerical calculation is developed to simulate the flexible model wing undergoing gust load in the time domain via discrete nonlinear finite element structural dynamic analysis and nonplanar unsteady vortex lattice aerodynamic computation. A dynamic perturbation analysis about a nonlinear static equilibrium is also used to determine the small perturbation flutter bound- ary. A novel noncontact 3-D camera measurement analysis system is firstly used in the wind tunnel test to obtain the spatial large deformation and responses. The responses of the flexible wing under different static equilibrium states and frequency gust loads are discussed. The fair to good quanti- tative agreements between the theoretical and experimental results demonstrate that the presented analysis method is an acceptable way to predict the geometrically nonlinear gust response for flex- ible wings.展开更多
Vortex-shedding flow induced by the vertical oscillation of a cylinder with bottom-attached disks of different diameter ratio Dd/Dc and thickness ratio td/Dc is studied by a 3D （three-dimensional） numerical model de...Vortex-shedding flow induced by the vertical oscillation of a cylinder with bottom-attached disks of different diameter ratio Dd/Dc and thickness ratio td/Dc is studied by a 3D （three-dimensional） numerical model developed in this paper, and compared with the results obtained through 2D （two-dimensional） numerical model. The high-order upwind scheme is applied to stabilize the computation, and convergence is accelerated by the multi-grid method. Qualitative and quantitative analyses of the differences between the 2D and 3D simulation results reveal the 3D effect on the flow field characteristics and hydrodynamic coefficients of the vertically oscillating cylinder with a bottom-attached disk. The 3D effect on the fluid field is mainly reflected in the significance of three vortex-shedding patterns： ωx has a greater effect on the flow fields around the sharp edges relative to the vortices generated in the 2D simulation. In the slice along the axial orientation, the vortex effect of ωy along the radial axis is smaller than that of ωx along the circumferential direction, indicating the radial effect on the velocity more pronounced than the circumferential effect around the sharp edges of the disk. The rotational interaction ωz of the fluid in the horizontal plane during the heave motion is insignificant. Based on the 2D and 3D simulation results, the turning points that separate the increasing regimes of the added mass coefficient and damping ratio are identified. The dependence of the turning point on the diameter ratio Dd/Dc and thickness ratio td/Dc are discussed in detail.展开更多
采用基于剪切应力输运模型的改进延迟分离涡模拟(improvement of delay detached-eddy simulation,IDDES)方法对两串列圆锥柱体高雷诺数流动干扰问题进行了数值计算,分析了不同间距比对流场结构和受扰圆锥柱体气动力特性的影响。结果表...采用基于剪切应力输运模型的改进延迟分离涡模拟(improvement of delay detached-eddy simulation,IDDES)方法对两串列圆锥柱体高雷诺数流动干扰问题进行了数值计算,分析了不同间距比对流场结构和受扰圆锥柱体气动力特性的影响。结果表明:间距比对两串列圆锥柱体的流场特性影响明显;当间距比为2时,下游圆锥柱体受到上游圆锥柱体的遮挡影响,其平均阻力系数较低;当间距比为4时,上游圆锥柱体的尾涡在下游圆锥柱体表面发生再附,下游(受扰)圆锥柱体的脉动阻力系数比小间距比时有所增加;随着间距比的继续增加,当间距比为8时,上、下游圆锥柱体形成各自的旋涡脱落,下游圆锥柱体的脉动升力系数明显高于间距比为2~4时的情况。展开更多
基金supported by the Innovation Technology Commission(ITC)of the Government of the Hong Kong Special Administrative Region(HKSAR)with Project(ITS/115/13FP)Hong Kong Ph.D.Fellowship Scheme from the Research Grants Council(RGC)
文摘Morphology as well as kinematics is a critical determinant of performance in flapping flight.To understand the effects of the structural traits on aerodynamics of bioflyers,three rectangular wings with aspect ratios（AR）of1,2,and 4 performing hovering-like sinusoidal kinematics at wingtip based Reynolds number of 5 300 are experimentally investigated.Flow structures on sectional cuts along the wing span are compared.Stronger K-H instability is found on the leading edge vortex of wings with higher aspect ratios.Vortex bursting only appears on the outer spanwise locations of high-aspect-ratio wings.The vortex bursting on high-aspect-ratio wings is perhaps one of the reasons why bio-flyers normally have low-aspect-ratio wings.Quantitative analysis exhibits larger dimensionless circulation of the leading edge vortex（LEV）over higher aspect ratio wings except when vortex bursting happens.The average dimensionless circulation of AR1 and AR2 along the span almost equals the dimensionless circulation at the 50%span.The flow structure and the circulation analysis show that the sinusoidal kinematics suppresses breakdown of the LEV compared with simplified flapping kinematics used in similar studies.The Reynolds number effect results on AR4 show that in the current Re range,the overall flow structure is not sensitive to Reynolds number.
基金supported by the National Natural Science Foundation of China(Nos.11302011,11172025)the National Natural Science Foundation for Youth of China(No.11402013)
文摘A theoretical nonlinear aeroelastic response analysis for a flexible high-aspect ratio wing excited by harmonic gust load is presented along with a companion wind tunnel test. A multidisci- plinary coupled numerical calculation is developed to simulate the flexible model wing undergoing gust load in the time domain via discrete nonlinear finite element structural dynamic analysis and nonplanar unsteady vortex lattice aerodynamic computation. A dynamic perturbation analysis about a nonlinear static equilibrium is also used to determine the small perturbation flutter bound- ary. A novel noncontact 3-D camera measurement analysis system is firstly used in the wind tunnel test to obtain the spatial large deformation and responses. The responses of the flexible wing under different static equilibrium states and frequency gust loads are discussed. The fair to good quanti- tative agreements between the theoretical and experimental results demonstrate that the presented analysis method is an acceptable way to predict the geometrically nonlinear gust response for flex- ible wings.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51239007 and 51179077)the Sino-UK Higher Education Research Partnership for Ph.D.Studies
文摘Vortex-shedding flow induced by the vertical oscillation of a cylinder with bottom-attached disks of different diameter ratio Dd/Dc and thickness ratio td/Dc is studied by a 3D （three-dimensional） numerical model developed in this paper, and compared with the results obtained through 2D （two-dimensional） numerical model. The high-order upwind scheme is applied to stabilize the computation, and convergence is accelerated by the multi-grid method. Qualitative and quantitative analyses of the differences between the 2D and 3D simulation results reveal the 3D effect on the flow field characteristics and hydrodynamic coefficients of the vertically oscillating cylinder with a bottom-attached disk. The 3D effect on the fluid field is mainly reflected in the significance of three vortex-shedding patterns： ωx has a greater effect on the flow fields around the sharp edges relative to the vortices generated in the 2D simulation. In the slice along the axial orientation, the vortex effect of ωy along the radial axis is smaller than that of ωx along the circumferential direction, indicating the radial effect on the velocity more pronounced than the circumferential effect around the sharp edges of the disk. The rotational interaction ωz of the fluid in the horizontal plane during the heave motion is insignificant. Based on the 2D and 3D simulation results, the turning points that separate the increasing regimes of the added mass coefficient and damping ratio are identified. The dependence of the turning point on the diameter ratio Dd/Dc and thickness ratio td/Dc are discussed in detail.
文摘采用基于剪切应力输运模型的改进延迟分离涡模拟(improvement of delay detached-eddy simulation,IDDES)方法对两串列圆锥柱体高雷诺数流动干扰问题进行了数值计算,分析了不同间距比对流场结构和受扰圆锥柱体气动力特性的影响。结果表明:间距比对两串列圆锥柱体的流场特性影响明显;当间距比为2时,下游圆锥柱体受到上游圆锥柱体的遮挡影响,其平均阻力系数较低;当间距比为4时,上游圆锥柱体的尾涡在下游圆锥柱体表面发生再附,下游(受扰)圆锥柱体的脉动阻力系数比小间距比时有所增加;随着间距比的继续增加,当间距比为8时,上、下游圆锥柱体形成各自的旋涡脱落,下游圆锥柱体的脉动升力系数明显高于间距比为2~4时的情况。
