Research progress on key issues of adjustable inlet system for aerospace vehicles

Aerospace vehicles are expected to play extremely important roles in military and civilian applications. One of the key technologies is the airbreathing combined-cycle engine that provides propulsion within the atmosphere. As a key component of the air-breathing combined-cycle engine，the air inlet urgently requires solutions to broad geometric/ aerodynamic adjustment requirements，the intricate organization and prediction needs of wide-area internal flow，and the smooth transition demands between multiple engine modes. In response to these three major needs，the variable air inlet system necessitates further research in fixed geometric/variable geometric adjustment technology，shock-dominated flow physics and flow control technology，and the dynamic evolution characteristics of the flow field during mode transition. Regarding the current state of research，rotation is the primary adjustment method for rectangular inlets；translation is the principal adjustment implementation method for axisymmetric inlets；deformable modulation holds a significant complementary and auxiliary value for both rectangular and axis-symmetric adjustable inlets. Researchers，both domestically and internationally，have gained a deep understanding of shock wave/boundary layer interactions，inlet buzz mechanisms，and unstart/restart hysteresis mechanisms，and made considerable progress in the modelling and prediction of the unstart/restart boundaries. Boundary layer bleeding remains an effective control measure against various detrimental phenomena in shock-dominated flows. In terms of mode transition，external over-under inlets exhibit relatively weak inter-flowpath coupling interaction，whereas internal over-under inlets display more significant inter-flowpath coupling effects. In the future，emphasis should be placed on developing efficient and lightweight adjustment technology，establishing a rapid design system for wide-envelope adjustable inlets，strengthening research on complex internal flow mechanisms during mode transition，and actively intersecting with engine control disciplines to break through intelligent inlet control technology，thereby supporting the development of China’s aerospace vehicles to a new level. © 2024 Chinese Society of Astronautics. All rights reserved.