Investgation Of Drag And Heat Flux Reduction Mechanism Of Combinational Forward-facing Cavity And Counterflowing Pulsed Jet Configuration

Hypersonic aircraft has attracted much attention due to its remarkable performance advantages and broad application prospects.But maintaining high Mach number flight for a long time will bring huge shock wave resistance and harsh aerodynamic thermal environment,which will greatly threaten the working performance of the aircraft and even the flight safety.Therefore,the development of drag reduction and heat protection technology is particularly important.It is one of the key technologies that restrict the application of the hypersonic aircraft to engineering practice.In this paper,a numerical simulation method is used to study the combination of the new forward-facing cavity and counterflowing pulsed jet in order to find a more efficient solution for drag reduction and heat protection.Firstly,it introduces the severe aerodynamic and aerothermal environment faced by the hypersonic aircraft,and lists three types of commonly used drag reduction and heat protection solutions,and then a detailed overview of the single counterflowing jet solution,the single forward-facing cavity solution and their combined solutions is provided.Secondly,two typical experimental examples of a single configuration are selected,and numerical method verification and grid independence verification are carried out.Then,the simulation results with the experimental data are compared to draw a conclusion:the SST k-w model and a grid with the grid Reynolds number being 1.47 can be used with confidence to get the best simulation results of the combined configuration.Then,based on the principle of the maximum thrust nozzle,a new configuration of the forward-facing cavity is programmed and compared,and the difference in drag reduction and heat protection performance of the two combination schemes is analyzed.The results show that the new configuration improves the drag reduction ability,but the heat protection ability decreases.Then,the effect of the total pressure ratio of the jet in the new combination configuration on the flow field mode,the drag reduction and heat protection performance is studied,and it is found that with the increase of the total pressure ratio,the flow field shows three modes,and the drag reduction performance in the long jet mode is better but the heat protection ability is worse.The comprehensive performance of the short jet mode is the best,and it is suitable as the working state.This provides a reference for the selection of the total pressure ratio of the pulsed jet.Subsequently,the sine wave pulsed jet is introduced into the combination scheme under the new configuration,and it is found that the flow field structure changes with the complete variations of long and short jet modes,and the action mechanism is revealed through the fine vortex structure.It is also found that the counterflowing pulsed jet scheme has strong periodicity and hysteresis effects,and the drag reduction effect of the counterflowing pulsed jet scheme is prior to the steady jet scheme,but the heat protection effect is not as good as the latter.Finally,three sine wave pulsed jets with different periods of T₁=2ms,T₂=1ms and T₃=0.5ms are defined,and the influence of period parameters on performance is explored.The conclusion is that the hysteresis of the pulsed jet scheme decreases as the period increases.The stability will be improved,and the drag reduction ability will be better under the large cycle,and the heat protection level under the small cycle will be higher.At the same time,three pulsed jets with different waveforms,namely square wave,sine wave,and triangle wave,are defined,and the influence of waveform parameters on the performance is explored as well.The conclusion is that there is no long jet mode in the flow field under the triangle wave waveform,and the triangle wave has the best stability and heat resistance.The square wave has poor stability,but the drag reduction effect is good.The sine wave is the most balanced jet solution.