Focusing on aerodynamic characteristics of rigid coaxial rotor of a high-speed helicopter in hover and forward flight, a wind tunnel test is conducted in the 8 m ? 6 m low-speed straightflow wind tunnel of China Aerod...Focusing on aerodynamic characteristics of rigid coaxial rotor of a high-speed helicopter in hover and forward flight, a wind tunnel test is conducted in the 8 m ? 6 m low-speed straightflow wind tunnel of China Aerodynamics Research and Development Center. In the experiment,a 4 m diameter composite model rigid coaxial rotor is designed and manufactured, and firstorder flapping frequency ratio of the blade is 1.796 to ensure sufficient stiffness at the blade root.Rotor aerodynamic performance is measured under hovering and high advance ratio conditions.Also, the numerical method is used to calculate aerodynamic characteristics in typical states of the rigid coaxial rotor for analysis purpose. The rotor lift-drag ratio and lateral lift offset in the experiment are emphatically analyzed for the rigid coaxial rotor. The results indicate that in forward flight condition, the rotor lift-drag ratio first increases and then decreases with the increment of advance ratio and lift offset. When advance ratio remains constant, with the increment of lift offset, the lift-drag ratio of rigid coaxial rotor first increases and then decreases.展开更多
The transverse stretching vibration of thick sandwich plates,which is attributed to largely different stiffness at the adjacent layers,is a challenging issue,and efficient approach for such issue is less reported in t...The transverse stretching vibration of thick sandwich plates,which is attributed to largely different stiffness at the adjacent layers,is a challenging issue,and efficient approach for such issue is less reported in the published literature.Thus,natural frequencies corresponding to stretching vibration modes are generally neglected in engineering design,which might impact structural safety as frequencies of the exciting force are close to transverse stretching vibration frequencies.This paper proposes an alternative higher-order model for dynamic analysis corresponding to the higher-order vibration modes.The proposed model is classified in the displacement-based equivalent single-layer theory,as the number of displacement parameters in the proposed model is independent of the layer number.The continuity of displacements and transverse shear stresses can be fulfilled at the interfaces between the adjacent layers of structures.To demonstrate the capability of the proposed model,typical examples are analyzed by utilizing the proposed model,the threedimensional finite element method and the chosen higher-order models.By comparing with the exact three-dimensional elasticity solutions,it is found that the proposed model can yield more accurate natural frequencies corresponding to the higher-order displacement modes than the selected models.Moreover,the factors influencing reasonable prediction of the higher-order frequencies are investigated in detail,which can provide a reference for the accurate prediction of the higher-order frequencies.展开更多
With the springing up of new technologies and materials in aircraft,the thermal management of aircraft is facing the dilemma of heat load increase and effective heat sink decrease.Hence the limiting factor of certain ...With the springing up of new technologies and materials in aircraft,the thermal management of aircraft is facing the dilemma of heat load increase and effective heat sink decrease.Hence the limiting factor of certain advanced aircraft is gradually changing from fuel to heat,and increasing emphasis on addressing the issue of aircraft environmental control should be placed.To reduce the energy consumption and improve the endurance of aircraft systems,this study reviews the development of aircraft environmental control technologies and analyzes the solutions in a human-machine cooperative manner.The comfortable temperature and humidity for personnel is generally between 18∼29℃and 20%∼30%respectively,and the normal working temperature of equipment is usually 15∼90℃.Using multiple indexes to evaluate the personnel comfort,equipment cooling and system energy consumption levels of existing aircraft environmental control technologies,it is found that the environmental needs of personnel and equipment cabin can be basically met with significant progress made in various technologies,e.g.equipment cooling,dehumidification and humidification,anti-freeze defrost and etc.Whereas there is rare research on the energy cascading utilization technology for human-machine synergistic environment and there exists challenges in applying the environmental control technology for cooling high-powered equipment to the personnel cabin.Finally,it is proposed that the future aircraft environmental control should develop cascading energy utilization,efficient cooling and shared control technologies,to take advantages of the humanmachine collaborative regulation and cope with the challenges caused by transient thermal load impacts on the system.展开更多
文摘Focusing on aerodynamic characteristics of rigid coaxial rotor of a high-speed helicopter in hover and forward flight, a wind tunnel test is conducted in the 8 m ? 6 m low-speed straightflow wind tunnel of China Aerodynamics Research and Development Center. In the experiment,a 4 m diameter composite model rigid coaxial rotor is designed and manufactured, and firstorder flapping frequency ratio of the blade is 1.796 to ensure sufficient stiffness at the blade root.Rotor aerodynamic performance is measured under hovering and high advance ratio conditions.Also, the numerical method is used to calculate aerodynamic characteristics in typical states of the rigid coaxial rotor for analysis purpose. The rotor lift-drag ratio and lateral lift offset in the experiment are emphatically analyzed for the rigid coaxial rotor. The results indicate that in forward flight condition, the rotor lift-drag ratio first increases and then decreases with the increment of advance ratio and lift offset. When advance ratio remains constant, with the increment of lift offset, the lift-drag ratio of rigid coaxial rotor first increases and then decreases.
基金co-supported by the National Natural Science Foundation of China(No.12172295)SKLLIM1902the Natural Science Foundation in Shaanxi Province,China(No.2019JQ-909)。
文摘The transverse stretching vibration of thick sandwich plates,which is attributed to largely different stiffness at the adjacent layers,is a challenging issue,and efficient approach for such issue is less reported in the published literature.Thus,natural frequencies corresponding to stretching vibration modes are generally neglected in engineering design,which might impact structural safety as frequencies of the exciting force are close to transverse stretching vibration frequencies.This paper proposes an alternative higher-order model for dynamic analysis corresponding to the higher-order vibration modes.The proposed model is classified in the displacement-based equivalent single-layer theory,as the number of displacement parameters in the proposed model is independent of the layer number.The continuity of displacements and transverse shear stresses can be fulfilled at the interfaces between the adjacent layers of structures.To demonstrate the capability of the proposed model,typical examples are analyzed by utilizing the proposed model,the threedimensional finite element method and the chosen higher-order models.By comparing with the exact three-dimensional elasticity solutions,it is found that the proposed model can yield more accurate natural frequencies corresponding to the higher-order displacement modes than the selected models.Moreover,the factors influencing reasonable prediction of the higher-order frequencies are investigated in detail,which can provide a reference for the accurate prediction of the higher-order frequencies.
文摘With the springing up of new technologies and materials in aircraft,the thermal management of aircraft is facing the dilemma of heat load increase and effective heat sink decrease.Hence the limiting factor of certain advanced aircraft is gradually changing from fuel to heat,and increasing emphasis on addressing the issue of aircraft environmental control should be placed.To reduce the energy consumption and improve the endurance of aircraft systems,this study reviews the development of aircraft environmental control technologies and analyzes the solutions in a human-machine cooperative manner.The comfortable temperature and humidity for personnel is generally between 18∼29℃and 20%∼30%respectively,and the normal working temperature of equipment is usually 15∼90℃.Using multiple indexes to evaluate the personnel comfort,equipment cooling and system energy consumption levels of existing aircraft environmental control technologies,it is found that the environmental needs of personnel and equipment cabin can be basically met with significant progress made in various technologies,e.g.equipment cooling,dehumidification and humidification,anti-freeze defrost and etc.Whereas there is rare research on the energy cascading utilization technology for human-machine synergistic environment and there exists challenges in applying the environmental control technology for cooling high-powered equipment to the personnel cabin.Finally,it is proposed that the future aircraft environmental control should develop cascading energy utilization,efficient cooling and shared control technologies,to take advantages of the humanmachine collaborative regulation and cope with the challenges caused by transient thermal load impacts on the system.
