We extend the impulse theory for unsteady aerodynamics, from its classic global form to finite-domain formulation, then to a minimum-domain version for discrete wake. Each extension has been confirmed numerically. The...We extend the impulse theory for unsteady aerodynamics, from its classic global form to finite-domain formulation, then to a minimum-domain version for discrete wake. Each extension has been confirmed numerically. The minimum-domain theory indicates that the numerical finding of Li and Lu（2012） is of general significance： The entire force is completely determined by only the time rate of impulse of those vortical structures still connecting to the body, along with the Lamb-vector integral thereof that captures the contribution of all the rest disconnected vortical structures.展开更多
The fluid-structure interaction (FSI) between the canopy and flow field on the inflating and inflated conditions is investigated based on the arbitrary Lagrange-Euler (ALE) method,in both a single-and double-cruciform...The fluid-structure interaction (FSI) between the canopy and flow field on the inflating and inflated conditions is investigated based on the arbitrary Lagrange-Euler (ALE) method,in both a single-and double-cruciform parachute systems.The projection area of canopy is calculated in the inflation process.The flow field characteristics and the interaction between canopies are analyzed.Results showed that,with free stream velocity of 50m/s,overinflation phenomenon would not occur during the inflation process of the double-cruciform-parachute system,because the collision and extrusion of the two canopies during inflation obstructed the oscillation of the inner gores.Concurrently,compared with the single-cruciform parachute,the vortex motion in the wake of double-cruciform-parachute is more intense.Thus the double-cruciform parachute system oscillated at a velocity of 50 m/s with an angle of less than 6.8°.By comparison,the oscillation angle of the single-cruciform parachute was within 3.5° at the velocity of 50m/s.The results are consistent with those of the wind tunnel test.展开更多
This review attempts to elucidate the physical origin of aerodynamic lift of an airfoil using simple formulations and notations,particularly focusing on the critical effect of the fluid viscosity.The evolutionary deve...This review attempts to elucidate the physical origin of aerodynamic lift of an airfoil using simple formulations and notations,particularly focusing on the critical effect of the fluid viscosity.The evolutionary development of the lift problem of a flat-plate airfoil is reviewed as a canonical case from the classical inviscid circulation theory to the viscous-flow model.In particular,the physical aspects of the analytical expressions for the lift coefficient of the plate-plate airfoil are discussed,including Newton’s sine-squared law,Rayleigh’s lift formula,thin-airfoil theory and viscous-flow lift formula.The vortex-force theory is described to provide a solid foundation for consistent treatment of lift,form drag,Kutta condition,and downwash.The formation of the circulation and generation of lift are discussed based on numerical simulations of a viscous starting flow over an airfoil,and the evolution of the flow topology near the trailing edge is well correlated with the realization of the Kutta condition.The presented contents are valuable for the pedagogical purposes in aerodynamics and fluid mechanics.展开更多
This paper presents a critical evaluation of the physical aspects of lift generation to prove that no lift can be generated in a steady inviscid flow.Hence,the answer to the recurring question in the paper title is ne...This paper presents a critical evaluation of the physical aspects of lift generation to prove that no lift can be generated in a steady inviscid flow.Hence,the answer to the recurring question in the paper title is negative.In other words,the fluid viscosity is necessary in lift generation.The relevant topics include D’Alembert’s paradox of lift and drag,the Kutta condition,the force expression based on the boundary enstrophy flux(BEF),the vortex lift,and the generation of the vorticity and circulation.The physi-cal meanings of the variational formulations to determine the circulation and lift are discussed.In particular,in the variational formulation based on the continuity equation with the first-order Tikhonov regularization functional,an incompressible flow with the artificial viscosity(the Lagrange multiplier)is simulated,elucidating the role of the artifi-cial viscosity in lift generation.The presented contents are valuable for the pedagogical purposes in aerodynamics and fluid mechanics.展开更多
文摘Avr9/Cf-9 rapidly elicited(ACRE)gene是富含亮氨酸重复单元,参与蛋白与蛋白互作,特异性识别病原物激发子的关键基因,在植物抗病过程中有重要意义。利用RT-PCR从马尾松中克隆出Avr9/Cf-9 rapidly elicited gene,命名为PmACRE(Gen Bank登录号:MF630966)。测序结果显示,PmACRE c DNA序列全长862 bp,其中完整编码区长度624 bp,编码207个氨基酸;以PFGFP Bar 137质粒为基本载体,构建了由组成型CaMV35S启动子驱动PmACRE基因的植物表达载体PFGFP Bar 137-PmACRE;采用冻融法转入农杆菌AGL1菌株,通过花序浸染法对拟南芥进行了遗传转化,并获得了4株阳性苗,经目的基因ACRE和GFP基因双重PCR检测,证实目的基因已整合到拟南芥基因组中。研究结果为进一步分析马尾松ACRE基因的功能和深入揭示R基因调控马尾松响应松材线虫侵染的作用机制奠定基础。
基金supported by the National Natural Science Foundation of China(Grant Nos.10921202,11221062,11521091 and 11472016)
文摘We extend the impulse theory for unsteady aerodynamics, from its classic global form to finite-domain formulation, then to a minimum-domain version for discrete wake. Each extension has been confirmed numerically. The minimum-domain theory indicates that the numerical finding of Li and Lu（2012） is of general significance： The entire force is completely determined by only the time rate of impulse of those vortical structures still connecting to the body, along with the Lamb-vector integral thereof that captures the contribution of all the rest disconnected vortical structures.
基金supported in part by the Aeronautical Science Foundation of China(No.20172952031)the Aeronautical Science Foundation of China (No.20142952026)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘The fluid-structure interaction (FSI) between the canopy and flow field on the inflating and inflated conditions is investigated based on the arbitrary Lagrange-Euler (ALE) method,in both a single-and double-cruciform parachute systems.The projection area of canopy is calculated in the inflation process.The flow field characteristics and the interaction between canopies are analyzed.Results showed that,with free stream velocity of 50m/s,overinflation phenomenon would not occur during the inflation process of the double-cruciform-parachute system,because the collision and extrusion of the two canopies during inflation obstructed the oscillation of the inner gores.Concurrently,compared with the single-cruciform parachute,the vortex motion in the wake of double-cruciform-parachute is more intense.Thus the double-cruciform parachute system oscillated at a velocity of 50 m/s with an angle of less than 6.8°.By comparison,the oscillation angle of the single-cruciform parachute was within 3.5° at the velocity of 50m/s.The results are consistent with those of the wind tunnel test.
文摘This review attempts to elucidate the physical origin of aerodynamic lift of an airfoil using simple formulations and notations,particularly focusing on the critical effect of the fluid viscosity.The evolutionary development of the lift problem of a flat-plate airfoil is reviewed as a canonical case from the classical inviscid circulation theory to the viscous-flow model.In particular,the physical aspects of the analytical expressions for the lift coefficient of the plate-plate airfoil are discussed,including Newton’s sine-squared law,Rayleigh’s lift formula,thin-airfoil theory and viscous-flow lift formula.The vortex-force theory is described to provide a solid foundation for consistent treatment of lift,form drag,Kutta condition,and downwash.The formation of the circulation and generation of lift are discussed based on numerical simulations of a viscous starting flow over an airfoil,and the evolution of the flow topology near the trailing edge is well correlated with the realization of the Kutta condition.The presented contents are valuable for the pedagogical purposes in aerodynamics and fluid mechanics.
文摘This paper presents a critical evaluation of the physical aspects of lift generation to prove that no lift can be generated in a steady inviscid flow.Hence,the answer to the recurring question in the paper title is negative.In other words,the fluid viscosity is necessary in lift generation.The relevant topics include D’Alembert’s paradox of lift and drag,the Kutta condition,the force expression based on the boundary enstrophy flux(BEF),the vortex lift,and the generation of the vorticity and circulation.The physi-cal meanings of the variational formulations to determine the circulation and lift are discussed.In particular,in the variational formulation based on the continuity equation with the first-order Tikhonov regularization functional,an incompressible flow with the artificial viscosity(the Lagrange multiplier)is simulated,elucidating the role of the artifi-cial viscosity in lift generation.The presented contents are valuable for the pedagogical purposes in aerodynamics and fluid mechanics.
