In this work, the wing tip vortex structure behind a NACA 0015 airfoil with and without small flaps was studied using a Partical Image Velocimetry （PIV） system. The experiment was carried out in a low speed wind tun...In this work, the wing tip vortex structure behind a NACA 0015 airfoil with and without small flaps was studied using a Partical Image Velocimetry （PIV） system. The experiment was carried out in a low speed wind tunnel with a test section of 0.5 m x 0.5 m. The Reynolds number （Re）, defined by the chord length of the wing （C）, was 8.1 x 104. The angle of attack was fixed at 10~. The PIV measurements were made from 0 to 2C, measured from the trailing edge of the model. The dihedral angle of three flaps was -15~, 0~ and 15~, respectively. Compared with the clean airfoil, the one with three flaps significantly changed the wing tip vortex structure, the vorticity and the core of the wing tip vortex. The occurrence of three flaps decreased the gradient of pressure on the two sides of the wing tip, which depressed wing tip vortex formation to some extent. Vortices shed from three flaps influence the evolution of the wingtip vortex generated by the base airfoil. The interaction of those vortices resulted in a weakening of the wing tip vortex.展开更多
The tip vortices and aerodynamics of a NACA0012 wing in the vicinity of the ground were studied in a wind tunnel.The wing tip vortex structures and lift/drag forces were measured by a seven-hole probe and a force bala...The tip vortices and aerodynamics of a NACA0012 wing in the vicinity of the ground were studied in a wind tunnel.The wing tip vortex structures and lift/drag forces were measured by a seven-hole probe and a force balance,respectively.The evolution of the flow structures and aerodynamics with a ground height were analyzed.The vorticity of tip vortices was found to reduce with the decreasing of the ground height,and the position of vortex-core moved gradually to the outboard of the wing tip.Therefore,the down-wash flow induced by the tip vortices was weakened. However,vortex breakdown occurred as the wing lowered to the ground.From the experimental results of aerodynamics,the maximum lift-to-drag ratio was observed when the angle of attack was 2.5°and the ground clearance was 0.2.展开更多
hree kinds of devices of drag reduction are presented swept wingtip,stage by stage swept wingtip and downbend wingtip. The effects of changing geometryparameters of the swept wingtip on the drag reducing are also pres...hree kinds of devices of drag reduction are presented swept wingtip,stage by stage swept wingtip and downbend wingtip. The effects of changing geometryparameters of the swept wingtip on the drag reducing are also presented. Wind-tunnelexperiment results indicate that a properly designed swept wingtip results in an incre-ment in induced efficiency of 4%～ 7% and that swept wingtip can increase longitudinalstatic-stability. Water-tunnel experiment results indicate that the reason for drag re-ducing of swept wingtip is that when the angle of attack is not zero, the strong end vor-tex of the wing is weakened by the combined effect of the leading edge and trailing edgevortices of the swept wingtip.展开更多
High-aspect-ratio aircraft are widely used in military and civilian fields,such as reconnaissance,surveillance,and attacks,due to their high lift-to-drag ratio,strong payload capability,significant endurance effect,an...High-aspect-ratio aircraft are widely used in military and civilian fields,such as reconnaissance,surveillance,and attacks,due to their high lift-to-drag ratio,strong payload capability,significant endurance effect,and good stealth performance.However,compared to conventional aircraft,high-aspect-ratio aircraft are more susceptible to gust disturbances during flight.In response to this phenomenon,a full-scale dynamic model of a high-aspect-ratio unmanned aerial vehicle was developed.Considering the coupling among control surfaces,structural forces,and aerodynamic forces,along with sensor,actuator,and delay effects,an H_(∞)control law was designed using the principle of singular value energy flow reduction and weighted function,with a PID(Proportional-Integral-Derivative)control law for comparison.The two controllers were then subjected to pulse-response and jury stability tests.Finally,wind tunnel tests were conducted to investigate the gust alleviation principle,in which gust disturbances were generated using gust generators and control surface self-excitation.The results present that the average wing root bending moment and wing tip overload under the PID control law decrease by approximately 30%,while under the H_(∞)control law,both the average wing root bending moment and wing tip overload reduction rate exceed 50%,with peaks reaching 60%.This validates the feasibility and efficiency of the designed H_(∞)controller.展开更多
A new analytical approach, based on a lifting surface model and a full span free wake analysis using the curved vortex element on the circular arc, is established for evaluating the aerodynamic characteristics of the...A new analytical approach, based on a lifting surface model and a full span free wake analysis using the curved vortex element on the circular arc, is established for evaluating the aerodynamic characteristics of the helicopter rotor with an anhedral blade tip and is emphasized to be applicable to various blade tip configurations, such as the tapered, swept, anhedral and combined shapes. Sample calculations on the rotor aerodynamic characteristics for different anhedral tips in both hover and forward flight are performed. The results on the induced velocity, blade section lift distribution, tip vortex path and rotor performance are presented so that the effect of the anhedral tip on the rotor aerodynamic characteristics is fully analyzed.展开更多
An effective method of optimal design of wing configuration is provided. The SUMT (sequential unconstained minimization technique) method is a good technique for solving the nonlinear programming. The application of p...An effective method of optimal design of wing configuration is provided. The SUMT (sequential unconstained minimization technique) method is a good technique for solving the nonlinear programming. The application of penalty in optimal design of wing configuration has been solved well. The present method for the aerodynamic calculation is the combination of both the nonlinear panel method and the suction analogy method of vortexlift spanwise distribution on large swept wing-tip. The calculation results are in good agreement with experimental data. According to the computation and experiment,the mechanism of the increased lift and reduced drag about the sheared wing-tip wing has been analyzed, and some opinions of interest are proposed.展开更多
基金supported by the National Natural Science Foundation of China(Grant No. 10642002)
文摘In this work, the wing tip vortex structure behind a NACA 0015 airfoil with and without small flaps was studied using a Partical Image Velocimetry （PIV） system. The experiment was carried out in a low speed wind tunnel with a test section of 0.5 m x 0.5 m. The Reynolds number （Re）, defined by the chord length of the wing （C）, was 8.1 x 104. The angle of attack was fixed at 10~. The PIV measurements were made from 0 to 2C, measured from the trailing edge of the model. The dihedral angle of three flaps was -15~, 0~ and 15~, respectively. Compared with the clean airfoil, the one with three flaps significantly changed the wing tip vortex structure, the vorticity and the core of the wing tip vortex. The occurrence of three flaps decreased the gradient of pressure on the two sides of the wing tip, which depressed wing tip vortex formation to some extent. Vortices shed from three flaps influence the evolution of the wingtip vortex generated by the base airfoil. The interaction of those vortices resulted in a weakening of the wing tip vortex.
基金supported by the National Natural Science Foundation of China(11072142)Shanghai Program for Innovative Research Team in Universities
文摘The tip vortices and aerodynamics of a NACA0012 wing in the vicinity of the ground were studied in a wind tunnel.The wing tip vortex structures and lift/drag forces were measured by a seven-hole probe and a force balance,respectively.The evolution of the flow structures and aerodynamics with a ground height were analyzed.The vorticity of tip vortices was found to reduce with the decreasing of the ground height,and the position of vortex-core moved gradually to the outboard of the wing tip.Therefore,the down-wash flow induced by the tip vortices was weakened. However,vortex breakdown occurred as the wing lowered to the ground.From the experimental results of aerodynamics,the maximum lift-to-drag ratio was observed when the angle of attack was 2.5°and the ground clearance was 0.2.
文摘hree kinds of devices of drag reduction are presented swept wingtip,stage by stage swept wingtip and downbend wingtip. The effects of changing geometryparameters of the swept wingtip on the drag reducing are also presented. Wind-tunnelexperiment results indicate that a properly designed swept wingtip results in an incre-ment in induced efficiency of 4%～ 7% and that swept wingtip can increase longitudinalstatic-stability. Water-tunnel experiment results indicate that the reason for drag re-ducing of swept wingtip is that when the angle of attack is not zero, the strong end vor-tex of the wing is weakened by the combined effect of the leading edge and trailing edgevortices of the swept wingtip.
基金supported by the National Natural Science Foundation of China(Nos.12272104,U22B2013).
文摘High-aspect-ratio aircraft are widely used in military and civilian fields,such as reconnaissance,surveillance,and attacks,due to their high lift-to-drag ratio,strong payload capability,significant endurance effect,and good stealth performance.However,compared to conventional aircraft,high-aspect-ratio aircraft are more susceptible to gust disturbances during flight.In response to this phenomenon,a full-scale dynamic model of a high-aspect-ratio unmanned aerial vehicle was developed.Considering the coupling among control surfaces,structural forces,and aerodynamic forces,along with sensor,actuator,and delay effects,an H_(∞)control law was designed using the principle of singular value energy flow reduction and weighted function,with a PID(Proportional-Integral-Derivative)control law for comparison.The two controllers were then subjected to pulse-response and jury stability tests.Finally,wind tunnel tests were conducted to investigate the gust alleviation principle,in which gust disturbances were generated using gust generators and control surface self-excitation.The results present that the average wing root bending moment and wing tip overload under the PID control law decrease by approximately 30%,while under the H_(∞)control law,both the average wing root bending moment and wing tip overload reduction rate exceed 50%,with peaks reaching 60%.This validates the feasibility and efficiency of the designed H_(∞)controller.
文摘A new analytical approach, based on a lifting surface model and a full span free wake analysis using the curved vortex element on the circular arc, is established for evaluating the aerodynamic characteristics of the helicopter rotor with an anhedral blade tip and is emphasized to be applicable to various blade tip configurations, such as the tapered, swept, anhedral and combined shapes. Sample calculations on the rotor aerodynamic characteristics for different anhedral tips in both hover and forward flight are performed. The results on the induced velocity, blade section lift distribution, tip vortex path and rotor performance are presented so that the effect of the anhedral tip on the rotor aerodynamic characteristics is fully analyzed.
文摘An effective method of optimal design of wing configuration is provided. The SUMT (sequential unconstained minimization technique) method is a good technique for solving the nonlinear programming. The application of penalty in optimal design of wing configuration has been solved well. The present method for the aerodynamic calculation is the combination of both the nonlinear panel method and the suction analogy method of vortexlift spanwise distribution on large swept wing-tip. The calculation results are in good agreement with experimental data. According to the computation and experiment,the mechanism of the increased lift and reduced drag about the sheared wing-tip wing has been analyzed, and some opinions of interest are proposed.
