Investigation Of Drag And Heat Flux Reduction Mechanism Of The Counterflowing Pulsed Jet And Its Combinations On Aerospace Vehicles

An aerospace vehicle will encounter a severe aerodynamic heating and strong aerodynamic resistance during its flight in the atmosphere,the high temperature brought by aerodynamic heating will damage the airframe structure and internal equipment of the aerospace vehicles,the strong aerodynamic resistance also puts forward higher requirements for the power system.Hence,an efficient and reusable drag and heat flux reduction system play an important role in the engineering implementation of the aerospace vehicle,it should be taken into consideration in the conceptual phase.This paper aims at the drag and heat flux reduction of the aerospace vehicles and carry out a numerical investigation of drag and heat flux reduction mechanism of the counterflowing pulsed jet and its combinations.Firstly,introduced the aerospace vehicle technological projects that have been or are being developed by the main aeronautics and astronautics powers in the world,the background environment of the research content in this paper is described.Then the traditional thermal protection system and technology are introduced,the advantages and disadvantages of these thermal protection systems are analyzed.Research progress of experimental and numerical investigations on drag and heat reduction from domestic and overseas literatures are summarized by several kinds of mechanism,namely the counterflowing jet,the forward-facing cavity and their combinational configurations.Secondly,a two-dimensional axisymmetric Reynolds-averaged Navier-Stokes equations is introduced.based on the experiment in Ref.[90],the steady state numerical simulation results obtained by using the SST k-?and standard k-?turbulence model are compared,in the meantime,the results with three different grid scales was also compared.By the contrast,the SST k-?turbulence model and a mesh with the?h=1.25×10^-4mm are employed.Thirdly,a counterflowing pulsed jet with a sinusoidal waveform was employed,the drag and heat reduction performance of the pulsed jet was investigated numerically.The obtained results show that the long penetration model does not exist in the whole turnaround.In the meantime,an obvious periodicity and hysteresis phenomenon was observed.Subsequently,three different kinds of sinusoidal pulsed jets with the period T₁=0.5ms,T₂=1.0ms and T₃=2.0ms are established,the influence of the pulsed jet period on drag and heat flux reduction performance was investigated numerically.The obtained results show that a better drag and heat flux reduction is obtained under larger period pulsed jet conditions.Then,three different kinds of pulsed jets with the sinusoidal,triangular and rectangular waveforms and same periods are employed in the numerical investigation.It is found that the drag and heat flux reduction under the triangular wave has the best effect,the pulsed jet with triangular wave has a better comprehensive performance than the other two.Finaly,a numerical investigation of the combinational forward-facing cavity and counterflowing pulsed jet is conducted.The obtained results show that the length to diameter ratio of the forward-facing cavity has a crucial influence on the drag and heat flux reduction of the combinations.