| As one of the most important components of the ramjet,the characteristics of the supersonic/hypersonic inlet directly determine the general performance of the engine.Most of the inlets are presently designed in the mixed-compression type with the most excellent integrated performance,and its starting characteristics have become one of the most important research aspects in the ramjet technology field.The restarting characteristics of mixed-compression supersonic/hypersonic inlet was investigated by theoretic analysis,numerical simulation and test methods in this thesis.A new classification method for restarting characteristics of mixed-compression inlet was proposed based on the researches of regulation mechanism and various effect factors.Firstly,the numerical calculation model of two-dimensions steady/unsteady compressible supersonic flow was established,verified by comparing the numerical simulation results and the publishable experimental dates of the inlet flow and the transverse jet injection into supersonic cross flow.Then restarting flow structure and operation mechanism of supersonic inlet was analyzed,starting characteristics of supersonic inlet under injection regulation of single square pulse injection and instantaneous injection was researched,the influence of injection mass flow and original pressure for regulation effects was investigated,and optimization design of injection structure parameters such as position,angle,slot width and so on was accomplished.According to the results of numerical simulation,the feasibility and practicality of injection regulation was validated,the new flow phenomena such as inner normal,moving aerodynamic choke,and flow oscillation under restarting flowfield with injection was discovered,which illuminate that the spillage is the key factor for inlet restarting.Next,inlet restarting experiment with injection regulation was carried out.The hysteresis of inlet and unstart flow was got by adjusting attack angle of model.With-2°attack angle,the restarting of inlet unstart flow was achieved firstly in the experiment using injection regulation.With the 0°attack angle,the restarting critical flow of inlet was got and flow oscillation phenomenon was found.Comparing to calculation result,the experimental result of flow characteristics and inner wall pressure distribution in the unstart flow is very close.But the minimal relative total pressure of injection for restarting inlet between the result of calculation and experiment are different.And the flow oscillation phenomenon is absent in the calculation result.With the further analyzing,the reason for these differences is that injection slot position of experiment deviates the design position of calculation,which caused by error of model machining precision and experiment operation.The flow oscillation operation mechanism of inlet was analyzed,which indicate that the flow structure varies distinctly during restarting,and the minimal injection mass flux for restarting also varies for different flow structure.With the unstart flow structure,the minimal injection mass flux for restarting is small,and becomes bigger with the restarting critical flow structure.When the injection mass flux is between two minimal injection mass flux for aforementioned flow structures,the unstart flow will convert to restarting critical flow because injection mass flux is bigger than minimal injection mass flux for unstart flow structures,then restarting critical flow will return to the unstart flow because injection mass flux is less than minimal injection mass flux for critical flow structures,and a new circulation starts.So the variation and reciprocity influence between restarting flow structure and restarting characteristics is the main mechanism of flow oscillation phenomenon.The oscillation frequency of calculation result is 135 Hz,close to the one of small Ferri type surge.The flow structure analysis and operation mechanism research of restarting characteristics for hypersonic inlet was carried out simultaneously,using the numerical simulation.The result shows that the key influencing factor of hypersonic inlet restart characteristics are shape and adverse pressure gradient of large separation bubble in unstart flow.The less virtual wedge angle and adverse pressure gradient are,the more close to lip the separation shock is,and the easier to restart the inlet is.The virtual wedge angle and separation shock angle is influenced by boundary layer and incoming flow parameters and decrease with the increase of incoming mach number.The adverse pressure gradient is influenced by core flow structure in the lip and inlet contraction ratio.The calculation result also finds a unstart flow whose separation shock is in the lip with no spilling when the contraction ratio is big,which validates that unstart mechanism of hypersonic inlet is separation bubble instead of spilling.Based on the researches hereinbefore,inner compression surface design and regulation of inlet were studied,which improve distinctly unstart flow performance and restarting characteristics through diminishing bottom surface horizontal angle on the tail of separation bubble and designing shoulder point to reduce pressure,and reduces restarting mach number to 7.6 from 9.4.A new design of inlet inner compression surface composed of the contractive surface in the front and the divergent surface in the rear was proposed,which also improve distinctly restarting characteristics with little influence to start flow performance,and reduces the restarting mach number to 8 from 9.4.Finally,a new classification method for restarting characteristics of mixed-compression inlet was proposed based on the difference of supersonic/hypersonic inlet,which advances the concept of choking and separate restarting characteristics.The former's key factor to restart and key flow structure of restarting critical flow is the vanishment of choking flow in the lip,and the latter's key factor to restart and key flow structure of restarting critical flow is vanishment of separation bubble in the lip. |
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