Study On Drag And Heat Reduction Mechanism And Flow Instability Characreristics Of Hypersonic Countreflowing Jet

Hypersonic vehicle has important application value in both civil and military fields,and has received more and more attention.However,how to reduce drag and aerody-namic heating on the surface of hypersonic vehicle is one of the most important problems to be considered in the design of hypersonic vehicle.As an active flow control technol-ogy,counterflowing jet has become a research hotspot due to its good effect in drag and heat reduction.However,the flow field of the counterflowing jet has strong instability characteristics.At the same time,the drag and heat reduction mechanism of the jet flow field and the accompanying flow field oscillation,especially the large bow shock oscilla-tion and the instability of the flow field under the long penetration mode,still need to be further studied.Because the unsteady simulation of drag and aerodynamic heating is affected by many factors,such as discrete format and real gas effect,the numerical simulation of hypersonic flow has always been one of the difficulties in computational fluid dynam-ics.At the same time,how to reduce drag and aerodynamic heating on the surface of the aircraft,as well as the drag and heat reduction mechanism and oscillation suppression of long penetration mode in counterflowing jet are also important issues to consider in the design of hypersonic aircraft.Therefore,in order to accurately predict the aerodynamics and thermal environment of aircraft,this article utilizes a unsteady solver developed on the Open FOAM platform and embeds a new splitting format,AUSM~+-up,to modify the Park chemical reaction model in the Earth environment.By capturing the transient distribution of various physical quantities at different times,it aims to investigate the drag and heat reduction mechanism,flow field structure and instability characteristics of the hypersonic hemispherical counterflowing jet technology.Firstly,based on the newly developed solver and considering the real gas effect of high temperature gas,the thermochemical non-equilibrium aerothermal numerical calcu-lation of hypersonic vehicle is carried out.The influence of chemical reaction model of different components and thermodynamic non-equilibrium model on shock standoff distance,wall heat flux and temperature distribution are analyzed.Due to the addition of chemical reaction,the shock standoff distance of the 7-component and 11-component chemical reaction models decreases compared with the 2-component chemical reaction.At the same time,the ionization degree of the 11-component chemical model is greater than that of the 7-component chemical model,and it is found that the ionization has little effect on the shock deionization distance and the heat flux distribution on the body wall of the hemispherical head.Secondly,the drag reduction mechanism,flow field structure and instability char-acteristics of hypersonic hemispherical head counterflowing jet are studied.The drag reduction mechanism and instability characteristics of bow shock wave oscillating back and forth under the action of counterflowing jet and reducing aircraft drag by changing the flow field structure around the aircraft are analyzed in detail.It is discovered that,in addition to oscillating back and forth under long penetration modes and time asymmetric oscillation,bow shock waves also do so to some extent under several short penetration modes.The oscillation frequency of the transient drag coefficient curve is consistent with that of the shock standoff distance curve,but there is a phase difference between the peaks.Then,the drag reduction efficiency,flow field structure and instability characteristics of hypersonic hemispherical head with a counterflowing jet at different jet temperatures are studied.It is discovered that the high temperature jet can significantly reduce the amplitude of the drag coefficient curve and suppress the oscillation of the flow field.In addition,the drag reduction efficiency per unit mass increases with the increase of jet temperature,and the mass flow rate of high-temperature jet decreases under the same efficiency,which can reduce the system weight,save space and cost.Therefore,increasing the jet temperature is a more effective method to reduce drag and stabilize the flow field than increasing the jet pressure ratio.Finally,further research has to be done on the issue of counterflowing jet related long penetration mode oscillation.The flow instability characteristics of hypersonic hemi-sphere with pulsed counterflowing jet are numerically studied.The effects of the fre-quency and amplitude of the pulsed jet on the long penetration mode behavior are studied in detail from the aspects of drag reduction,heat reduction efficiency and shock stand-off distance.It is found that pulsed jet can slow down the oscillation of long penetration mode and reduce the amplitude of oscillation.It has the specific benefit of decreasing heat flux.The higher the pulsed amplitude,the better the cooling effect.At the same time,the pulse frequency can lock the oscillation frequency at the same time.As a result,the pulsed jet may simultaneously achieve increased oscillation suppression and improved heat reduction efficiency in the long penetration mode.In conclusion,based on the mechanism of drag and heat reduction of counterflowing jet,this paper applies high-temperature jet and pulsed counterflowing jet to hypersonic vehicles,achieving the goal of effective drag and heat reduction of hemispherical nosed vehicles and suppression of long penetration mode flow field oscillation.It is hoped that the research results in this paper will be helpful to promote the engineering application of hypersonic counterflowing jet technology,and can provide important theoretical basis and reference for hypersonic vehicle aerodynamic layout,drag and heat reduction schemes and related experimental research.