Study On The Dynamic Problems Of Air-Launch In Separation Process

The development of fast,flexible,low-cost and robust spacecraft launch technology is the trend for future.And the air-launch technology is satisfied with the requirements.For the air-launch technology,the carrier aircraft can take off from the ordinary airport,and the spacecraft can be launched to the space without the support of the large space launch base.Thus,the air-launch is robust and high survivability.The carrier aircraft plays a role of the first stage rocket and can be reused.Compared with the first stage rocket,the aerodynamic efficiency of the carrier aircraft is higher in the endoatmospheric,and the payload can be transported to a certain altitude with little fuel.Therefore,the average cost of the air-launch is lower.Besides,the air-launch promises a lot more scope to find a good "launch window" to get the spacecraft into orbit,which is more flexible.The separation between the carrier aircraft and payload is one of the most important and difficult phases in Air-launch-to-orbit technology.The motion locus and attitude angles of the store should be under control strictly to insure the successful launching.However,during the separation,the unsteady interaction aerodynamics between the carrier aircraft and payload are complicated,which will have effect on the dynamics responses of the payload.When the aspect ratio of the carrier aircraft and the weight of the payload are large,the elastic deformation of the carrier aircraft should be considered,and the aerodynamics interference caused by the elastic deformations may have great influence on the unsteady aerodynamics of the payload.The main purpose of this paper is to study the dynamic response of the payload during the separation process of air-launch.And the main work is arranged as follow.(1)A kind of CFD/CSD/RBD(CFD:Computational Fluid Dynamics,CSD:Computational Structure Dynamics,RBD:Rigid Body Dynamics)coupling simulation method is developed in this paper,which is suitable for the simulation of the store separation with considering of the elastic deformation of the carrier aircraft.The coupling simulation method is based on the Generalized Fluid-Structure Interaction(GFSI)code developed by our research group.By adding the CFD/CSD/RBD coupling simulation module,the flight dynamic of the elastic plane can be simulated.This method will provide important supports for further research.(2)With the CFD/CSD/RBD coupling simulation method,the dynamic responses of the store separation with considering of the elastic deformation of the carrier aircraft are solved.And the influence of the interference aerodynamics caused by the elastic deformations of the carrier aircraft on the unsteady aerodynamics of the payload is studied.The results show that the elastic deformations of the carrier aircraft have significant influence on the dynamic response frequency and aerodynamics amplitude of the payload.On that basis,by changing the pylons location,carrier aircraft rigidity,dynamic pressure and payload wing loading,the dynamic responses of the payload are analyzed qualitatively.(3)The interference aerodynamics analysis model of the payload is developed in this paper.According to the different sources of the interference aerodynamics,the aerodynamics can be divided into different components.The analysis model is the linear combination of the aerodynamics components.The aerodynamics components of the payload can be solved by CFD method,CFD/RBD coupling method,CFD/CSD coupling method and CFD/CSD/RBD coupling method flexibly.In this paper,the relative magnitude,change rule,sphere of influence and mechanism of production of the steady and unsteady interference aerodynamics components of the payload are analyzed quantitatively.The research finds that when the distance between the carrier aircraft and payload is small,the the interference aerodynamics of the payload caused by the elastic deformation of the carrier aircraft is about half of the total aerodynamic forces of the payload,which should be carefully considered in the engineering applications.With the increase of the relative distance,the value of the interference aerodynamics will decrease,and the sphere of influence of the payload's interference aerodynamic forces is two times the MAC(Mean Aerodynamic Chord)of carrier aircraft.(4)The fuzzy logic method is used in the non-linear aerodynamics modeling for rigid body aircraft.And during the rigid body dynamic simulation,the CFD method will be replaced by the UAM based on the fuzzy logic method.The fuzzy logic method is available for non-linear projects,and needs little human intervention.Compared with the linear superposition model,the fuzzy logic model has obvious advantages,especially for the dynamic simulation of rolling and sideslip freedom.(5)The interference aerodynamics model of the payload is developed in this paper.The model is based on the interference aerodynamics analysis model above mentioned.By coupling the aerodynamics model,structure dynamic function and rigid body dynamic function,the aircraft dynamic simulation platform is built.And the platform can be used in the dynamic simulation of the store separation with considering of the elastic deformation of the carrier aircraft.Compared with the CFD/CSD/RBD method,the longitudinal UAM/CSD/RBD method and rolling degree UAM/CSD/RBD method are sufficiently accurate and have higher efficiency.The UAM/CSD/RBD method has a strong application potential for engineering research.(6)A new kind of CFD/CSD/RBD coupling method based on the unsteady aerodynamic reduced order models(ROM)is proposed in this paper.With this method,the physical time step can be increased in the CFD/CSD/RBD coupling simulation,and the computational efficiency will be improved a lot.Specifically,the ROM is brought into the CFD/CSD/RBD coupling simulation platform,and the physical time steps are setted by time-stratification method.The rigid body dynamic function and flow field are solved by CFD/RBD coupling method,and the physical time step is based on the rigid mode frequency.The elastic deformations are calculated by the UAM/CSD coupling method,and the time physical step is based on the highest frequency of the elastic mode.During the UAM/CSD coupling simulation,the flow field and rigid body dynamic responses are frozen.The computational accuracy of the new coupling method is higher comparing with the UAM/CSD/RBD method,and the computation period is only one-tenth of the CFD/CSD/RBD method.