This paper presents results of a series of experiments carried out on models of a car and a truck in a wind tunnel to observe the pressure coefficient variation when the truck was overtaken by the car.However,conventi...This paper presents results of a series of experiments carried out on models of a car and a truck in a wind tunnel to observe the pressure coefficient variation when the truck was overtaken by the car.However,conventional wind tunnels are not equipped to measure the yaw moment and side force created due to pressure difference created as a result of the interaction of two vehicles and the cross wind.An additional attachment for the wind tunnel was designed and built to measure the yawing moment and the side force experienced by the car when the cross wind is applied.The attachment consists of a"top plate"which is independent from the wind tunnel frame and free to rotate.The car model is fixed to the"top plate"the top plate is connected to the base plate via a load measuring shaft which is connected to load cells that enable to measure the yaw moment.The pressure coefficient variation was measured by a series of pressure tapings provided by the circumference of the car.The two models were tested independently in the wind tunnel for their pressure coefficient variation.It was found that the pressure coefficient around the car varies substantially when it is overtaking the truck.It was also observed that when the cross wind is applied the yawing moment and the side force on the car increases with the air speed.The attachment was calibrated prior to the investigation and have been able to obtain consistent results.To relate the observations to real world conditions,further investigations are necessary.展开更多
This paper presents a morphing missile with an expandable flared skirt,which aims to change aerodynamic shape according to the change of flight environment to improve flight efficiency.Themorphing missile with an expa...This paper presents a morphing missile with an expandable flared skirt,which aims to change aerodynamic shape according to the change of flight environment to improve flight efficiency.Themorphing missile with an expandable flared skirt is regarded as a multi-rigid-body system,and the six-degree-of-freedom(6-DOF)nonlinear dynamic model of the missile is established considering the changes of aerodynamic force,mass distribution,and inertia characteristics during morphing.In order to investigate the longitudinal dynamic characteristics of the missile,the nonlinear dynamic model is de-coupled to obtain its longitudinal motion equation.The aerodynamic parameters of the missile in the whole flight state envelope are simulated by quasi-steady assumption,and the aerodynamic coefficients under different flight environments and flared opening angles are obtained.The aerodynamic coefficients obtained from the simulation at each operating point are fitted to the flight altitude,Mach number,and the morphing rate of the flared skirt by the least square method.Finally,the parametric model of the aerodynamic coefficients is obtained.Finally,the aerodynamic coefficient function model is introduced into the longitudinal motion equation of the missile,and the longitudinal dynamic characteristics of the missile in different flight conditions are obtained by numerical simulation.The simulation results show that the morph of the flared skirt has a significant influence on the longitudinal motion characteristics of the missile.展开更多
文摘This paper presents results of a series of experiments carried out on models of a car and a truck in a wind tunnel to observe the pressure coefficient variation when the truck was overtaken by the car.However,conventional wind tunnels are not equipped to measure the yaw moment and side force created due to pressure difference created as a result of the interaction of two vehicles and the cross wind.An additional attachment for the wind tunnel was designed and built to measure the yawing moment and the side force experienced by the car when the cross wind is applied.The attachment consists of a"top plate"which is independent from the wind tunnel frame and free to rotate.The car model is fixed to the"top plate"the top plate is connected to the base plate via a load measuring shaft which is connected to load cells that enable to measure the yaw moment.The pressure coefficient variation was measured by a series of pressure tapings provided by the circumference of the car.The two models were tested independently in the wind tunnel for their pressure coefficient variation.It was found that the pressure coefficient around the car varies substantially when it is overtaking the truck.It was also observed that when the cross wind is applied the yawing moment and the side force on the car increases with the air speed.The attachment was calibrated prior to the investigation and have been able to obtain consistent results.To relate the observations to real world conditions,further investigations are necessary.
文摘This paper presents a morphing missile with an expandable flared skirt,which aims to change aerodynamic shape according to the change of flight environment to improve flight efficiency.Themorphing missile with an expandable flared skirt is regarded as a multi-rigid-body system,and the six-degree-of-freedom(6-DOF)nonlinear dynamic model of the missile is established considering the changes of aerodynamic force,mass distribution,and inertia characteristics during morphing.In order to investigate the longitudinal dynamic characteristics of the missile,the nonlinear dynamic model is de-coupled to obtain its longitudinal motion equation.The aerodynamic parameters of the missile in the whole flight state envelope are simulated by quasi-steady assumption,and the aerodynamic coefficients under different flight environments and flared opening angles are obtained.The aerodynamic coefficients obtained from the simulation at each operating point are fitted to the flight altitude,Mach number,and the morphing rate of the flared skirt by the least square method.Finally,the parametric model of the aerodynamic coefficients is obtained.Finally,the aerodynamic coefficient function model is introduced into the longitudinal motion equation of the missile,and the longitudinal dynamic characteristics of the missile in different flight conditions are obtained by numerical simulation.The simulation results show that the morph of the flared skirt has a significant influence on the longitudinal motion characteristics of the missile.
