Two-phase flow characteristics inside a serpentine inlet in heavy rain

Rain is a common atmospheric phenomenon encountered by aircraft and is one major cause of several catastrophic flight accidents. Stealth aircraft usually adopt the knapsack serpentine inlet layout, of which the entrance is beveled and upward, thus easily subject to external environmental effects like rain. This study investigates the effects of rain on the aerodynamic performance of a serpentine inlet by an Eulerian-Lagrangian two-phase flow approach. The Computational Fluid Dynamics (CFD) method is validated by experiments. The results indicate that the aerodynamic performance of the inlet, such as total pressure recovery, circumferential total pressure distortion index, and swirl distortion index, is all influenced by rain. Rain intensity and raindrop size are found to have a significant influence on the inlet aerodynamic performance. Raindrops impacting the inner wall surface of the inlet lead to the formation of water films. Furthermore, the water film has a non-negligible effect on the inlet velocity boundary layer. Crosswinds and headwinds affect the position of the water film formation. The swirl intensity of the airflow near the top wall of the aerodynamic interface plane (AIP) increases under rain conditions. These findings show the need to consider the impact of rain when designing and evaluating the aerodynamic performance of an aircraft engine.