Abstract:

Irregular inlets can enhance the stealth capability of aircraft， but their complex flow structures may lead to instability under low flow rate conditions， thus affecting the normal operation of the engine. Numerical simulations are conducted to investigate the flow characteristics and performance behavior of an irregular inlet， with particular focus on its instability mechanism under throttled （low flow rate） conditions. The results indicate that under the high flow rate condition， local transonic regions appear within the duct， leading to a reduction in the total pressure recovery coefficient， whereas under the low flow rate condition， the inlet boundary layer flow is subjected to a strong adverse pressure gradient near the throat， which induces boundary layer separation. The multiple vortex structures within the internal duct cross-section gradually merge into a single vortex structure， significantly increasing the total pressure loss and posing challenges for engine matching. Furthermore， the angle of attack has a pronounced impact on the inlet’s stability boundary. At positive angles of attack， separation is more likely to occur on the lower wall of the first bend and the upper wall downstream of the bulge， leading to an earlier onset of flow instability and increased sensitivity of inlet performance to flow disturbances. This study clarifies the core physical mechanisms responsible for low-flow-rate instability in shaped inlets and provides theoretical guidance for robust inlet design and stability management under complex operating conditions.

Key words: irregular inlets, low flow rate conditions, subsonic, internal flow characteristic, instability mechanism