Key Characteristics Of Payload Fairing Separation For New Generation Launch Vehicle

Payload fairing is an important component to protect the payload and keep the aerodynamic shape of the rocket or missile(launch vehicle).When the vehicle is away from the atmospheric interference,its fairing no longer works and needs to be separated from the main body.As a type of new generation launch vehicle in China,the payload fairing of CZ-5 becomes larger and more complex,which requires stronger separation energy than previous launch vehicles.In addition,with the increasing size of the fairing,its stiffness will get lower,and the deformation will have a greater influence on the fairing separation.At present,most of related researches mainly focus on the numerical simulation,ground test and CFD(computational fluid dynamics)analysis of the fairing separation for small and medium-diameter launch vehicles.However,for large-diameter launch vehicles,the effects of structural deformation on fairing separation cannot be accurately considered in the previous studies,which may also cause some errors.To cope with these problems,several attempts are devoted to investigate the key separation characteristics of new generation launch vehicle in China.In the previous studies,the failure mechanism of the hinge system was taken into account for the fairing separation.However,the separation energy of CZ-5 is stronger than the previous types of Chinese launch vehicles,thus it is crucial to consider the security problem of the hinge system impact.The conventional impact model of the hinge system is considered as rigid-body model or quasi-static constitutive model,therefore,the analysis results are not precise enough.In order to obtain the precise impact model,the dynamic mechanical properties of ZTC4-land 30CrMnSiA(heat treated and without heat treatment)which are component materials of the hinge system are obtained at first by impact compression test with different loading rates,and then dynamic test results are compared with the results of quasi-static tensile test.Test results show that two materials are both strain-rate sensitive,and different processing technologies can affect the mechanical property,and the one with heat treatment is better.Based on the photographs of metallographic organization,the reasons for the changes of material properties with different strain rates are explained.Finally,test data are fitted based on the Johnson-Cook(JC)model,and the dynamic constitutive relationships of the materials for the hinge system are established under high strain rate.Compared with test data,the fitting effect is fine,which is shown that the JC model can reflect the dynamic mechanical behavior of the material well,thus it could be used as the dynamic constitutive model for the self-impact finite element analysis of the hinge system.In order to ensure the safe separation of the first five-metre-scale large launch vehicle fairing,the self-impact behavior of the hinge system with dynamic constitutive model is studied by numerical simulation in this paper,based on the dynamic mechanical property test datas and fitting datas.By employing the explicit dynamic analysis method,it is known that the self-impact behavior of the hinge system presents the trend of "tough firstly and then becomes weak",namely during the early stage the impact is intense,but during the late stage the impact appears at a low speed and steady state,and material yield occurs after the whole impact process,while the deformation is not very large,therefore,the hinge system is still safe.Secondly,based on the internal force analysis it can be found that the shear force and bending moment are the main internal forces of the hinge swing arm axis in the impact process.Finally,by comparing the calculation results of quasi-static constitutive model with dynamic constitutive model,it is proved that the dynamic constitutive model is applicable and more accurate for the unlocking problem of the fairing,which is helpful to improve the prediction accuracy of separation..As the self-impact process of the hinge system is safe,it is then necessary to investigate the characteristics of fairing separation with large separation energy for CZ-5.Since traditional methods for fairing separation donot consider structural flexibility,they cannot accurately solve the movement problem of large-scale shell.Therefore,modal analysis and mode extraction are performed for CZ-5 fairing based on the Lanczos method in the paper firstly.As is evident from the analysis results,structural flexibility of CZ-5 fairing is large,which should be considered when analyzing the characteristics of CZ-5 fairing separation,otherwise it will produce a significant prediction error.Based on the refined finite element model of CZ-5 fairing,the separation process of fairing is simulated by explicit dynamic analysis,and results show that the fairing can be successfully separated under the given separation energy.However,a remarkable breathing deformation can be observed during this process,and the maximum shrinkage value is even close to the the upper limit of enveloping space of the fairing.To ensure the safety of separation,a new structure of spring component is proposed in this paper,in order to restrict the breathing deformation.This new structural configuration contains a guiding hole and a load support,and two parts are connected by a spring-bar to reinforce the local stiffness.And then,the breathing deformation of the fairing separation is controlled in the allowable range.Finally,the new structure is validated by the test for controlling the breathing deformation.Finally,the fluid-solid coupling problem in fairing ground separation test of CZ-5 is studied.Large-scale fairing ground separation is a fluid-solid coupling problem involving a shell structure with large overall motion,moreover,the fluid-solid coupled interface always changes.However,it needs to provide fixed fluid-solid coupled interfaces for traditional computational fluid dynamics(CFD)methods,and the coupling process is usually decoupled by iterative methods,thus the computational cost is high while the calculation accuracy is low.Therefore,the ground separation test of the fairing is analyzed based on the coupling Eulerian-Lagrangian(CEL)method in this study,which solves the solid problem and the fluid problem simultaneously.During the computational process,an efficient equivalent model is presented by the reduced spring energy method,and this model can guarantee the relative balance betweem accuracy and efficiency.The flow-field characteristics in fairing separation are analyzed,and the results were verified by the ground test of CZ-5.To sum up,with regard to the new generation launch vehicle in China,i.e.CZ-5,the key separation characteristics are investigated.The analysis method proposed in this paper was verified through the ground test,which has broken through the bottleneck of analysis and design for the large payload fairing.These are of great significance to improve the design ability of the fairing separation system and improve the prediction accuracy of the key characteristics of fairing separation.The above studies were highly appreciated by China Academy of Launch Vehicle Technology as:"The prediction error of key separation characteristics is within 10%,which is significant for the fairing design of launch vehicles in China".