Bump进气道超额定小流量失稳特性OA

Severe flow oscillation induced by low-mass-flow of inlet directly threatens flight safety.The unsteady simu-lation on the low-mass-flow induced instability phenomenon of the Bump inlet under over-speed operating conditions at Ma0=1.8 is conducted.The effects of different throttling levels on the inlet is studied.The results show that when the inlet mass flow is reduced to 48%of the through-flow mass flow rate,the inlet enters a periodic surge state.Based on the flow characteristics,the instability process can be divided into three typical stages,i.e.,terminal shock expelling out of duct,backflow development,and the internal flow re-establishment.Driven by the high pressure inside the tube,the terminal shock propagates forward,with its movement speed initially decreasing and then increasing.As the terminal shock merges with the lip shock,it triggers large-scale flow separation.The interaction between this sepa-rated flow and the incoming freestream generates unsteady vortical structures,which disrupt the inlet shock system.In the later stage of the backflow development phase,significant reverse flow is observed near the inlet,and a zero-velocity interface forms in the vicinity of the outlet section.Subsequently,the pressure inside the duct gradually de-creases,allowing the internal flow field to be reestablished.As the second throat diameter decreases(corresponding to a further reduction in mass flow),the maximum pressure ratio inside the duct increases from 6.61 to 6.84,and the normalized backflow propagation distance ratio increases from 2.43 to 3.33.