Dynamic Drag Reduction Mechanism Study Of Hypersonic Aircraft

In regard to drag reduction of hypersonic aircraft during dynamic maneuver,the effects of fixed aerospikes and self-aligned aerospikes are studied based on the dynamic hybrid grid technology and unsteady numerical simulation method.The drag reduction mechanisms in the process of large-amplitude pitch oscillation are explored.And principles and drag reduction rates are also studied when changing various parameters.It is helpful for flow mechanism understanding and aerospike optimization,which could give some technology reference for hypersonic aerospike design.Firstly,from the perspectives of wind tunnel test and numerical simulation,the research status of fixed aerospike method is systematically summarized.And relevant progress of self-aligned technology in China and abroad is also concluded.Secondly,hypersonic unsteady hydrodynamics/kinematics coupling algorithm is set up and numerically validated.Typical examples of steady flow around spherical biconical and plate laminar boundary layer are selected to verify the accuracy of hypersonic flow simulation.Furthermore,the pitch oscillation of NACA0012 airfoil,small-attack-angle pitch oscillation of the hypersonic blunt cone and the standard model of Finner "cross" wing missile are simulated.The results are in good agreement with the experimental and reference data,which proves that the program and algorithm basis of this paper is established.Then,drag reduction mechanism study of fixed and self-aligned aerospikes are conducted,which mainly analyzes the flow field characteristics.By changing parameters such as oscillation period,head shape,aerospike length and top-disc diameter respectively,their dynamic drag reduction effects and flow field evolutions near the blunt body are discussed.Finally,after comparing average and dynamic drag characteristics,the differences between fixed and self-aligned aerospike methods are analyzed in detail.In addition,with the evolution of unsteady flow,the effects of different parameters on the relative drag reduction rate between two methods are compared.It is found that the self-aligned aerospike is always aligned with the incoming flow,and its function of flow field reconstruction can be maintained under high attack angle.In most of the range above80%,compared with the fixed method,the drag reduction effect can be improved by more than 40%.