Abstract

The inlet of an aircraft engine is a primary contributor to the aircraft’s forward electromagnetic scattering. S-shaped inlet and radar absorbing materials (RAM) coatings have been widely adopted as effective measures to reduce forward radar cross section (RCS). To investigate the influence of RAM shedding on the RCS reduction efficiency, the electromagnetic scattering characteristics of the inlet under five different shedding probabilities were calculated using the iterative physical optics (IPO) combined with impedance boundary condition (IBC). Numerical simulation results demonstrate that the forward RCS of the S-shaped inlets increases monotonically with shedding probability. In the yaw plane, intact non-magnetic RAM exhibits better RCS reduction efficiency (RRE) than that in the pitch plane across all scenarios. Specifically, at a shedding probability of 0.7, the remaining non-magnetic RAM maintains an RRE exceeding 40% in the pitch plane. Collectively, these results suggest that recoating the nonmagnetic RAM is recommended when the shedding probability exceeds 0.7 in either detection plane to sustain critical stealth performance.OPEN ACCESS Received: 20/05/2025 Accepted: 13/08/2025 Published: 27/10/2025

Abstract

Engine inlet icing persists as a critical hazard to aviation operational safety, compromising aerodynamic performance and potentially inducing catastrophic engine failure. Aero-engine swirling anti-icing systems inject high-temperature bleed air into an annular chamber at the engine’s leading edge through tangentially positioned nozzles. This high-velocity jet entrains low-temperature air within the chamber, establishing a circulatory flow that effectively heats the lip surface to prevent ice formation. This study employs computational fluid dynamics (CFD) method to systematically evaluate the flow and heat transfer characteristics of four distinct nozzle configurations within an aero-engine anti-icing chamber: conical single-orifice, diffuser-equipped, elliptical dual-orifice, and elliptical quad-orifice nozzles. Results indicate that the conical single-orifice nozzle exhibits the highest entrainment efficiency due to its concentrated jet structure, whereas the diffuser-equipped nozzle demonstrates 16.4%– 18.1% lower efficiency, attributable to premature kinetic energy dissipation. At identical bleed air flow rates, the diffuser-equipped nozzle yields the lowest circulation velocity and pressure loss, necessitating minimal bleed air pressure. The elliptical quad-orifice nozzle optimally mitigates hot and cold spots via multi-jet energy dispersion, achieving a maximum 34.7% reduction in lip surface temperature differentials compared to the conical single-orifice design within the analyzed bleed air mass flow rate range. Nozzle configurations exert limited influence on the average Nusselt number, with a maximum relative deviation of 5.48% observed across all nozzle configurations when compared to established empirical correlations.OPEN ACCESS Received: 11/07/2025 Accepted: 21/08/2025 Published: 15/12/2025