Stage separation of recoverable liquid launch vehicle by using moving pulsating ball analogue for propellant sloshing

In the process of stage separation of recoverable liquid launch vehicles,because of the large amount of residual fuel in the storage tanks,the influence of liquid sloshing on separation safety must be considered.Considering calculation simplicity and operation practicability,the Moving Pulsating Ball Model(MPBM)of large amplitude liquid sloshing is introduced into the calculation of launch vehicle stage separation.Combining the dynamic equation of the model with the energy relationship during"breathing movement",the formula calculating the force of liquid on the rigid body is derived.Compared with the calculations of commercial CFD calculation software,the accuracy of MPBM model is verified.Then,all the external forces and moments are applied to the rigid body of the stages,so that the translational and rotational dynamic equations of the stages are obtained respectively.According to the relative position of the two stages,the geometric shape of the interstage section and the engine of the second stage,the minimum clearance in the separation process can be decided to guarantee that the separation process is safe.

Derivation and validation of a similarity law for free-flight wind tunnel tests of parallel stage separation

Aiming at the safety problem of the stage separation of parallel reusable high-speed air vehicles,this paper studies the unsteady test method and focuses on deriving a similarity law of parallel stage separation free-flight wind tunnel tests.The new similarity law considers the influences of aerodynamic force and gravity on the motions of the two stages,as well as the influence of aerodynamic interference between the two stages on each other’s motion.From the perspective of multiangle physical equations,the conditions to ensure that the two-stage separation trajectory of a wind tunnel test is similar to that of a real air vehicle are derived innovatively,so as to ensure the authenticity and credibility of wind tunnel test results.The similarity law is verified by an HIFiRE-5 air vehicle,and the separation trajectories of wind tunnel tests and the real air vehicle are obtained by numerical simulation.The research shows that the similarity law derived in this paper can ensure that wind tunnel free-flight tests have the ability to predict the two-stage separation characteristics of real parallel vehicles.By analyzing the separation trajectory curve of the typical state,it is found that the new method can ensure that the trajectory error of a wind tunnel test does not exceed 1%,which indicates that this method is credible.The establishment of the new method lays the foundation for subsequent wind tunnel tests and provides support for research on the safety of the stage separation of parallel reusable air vehicles.