Numerical study of unsteady aerodynamic interference in dual-helicopter/ship flow fields

To clarify the unsteady aerodynamic interference in simultaneous shipboard dual-helicopter operations, a high-fidelity Computational Fluid Dynamics (CFD) model based on Improved Delayed Detached-Eddy Simulation (IDDES) was established for a Wasp-class ship under headwind, Green 30° wind, and Red 30° wind conditions. The flow evolution, aerodynamic-force histories, spectral characteristics, and coherence of the coupled flow fields were systematically analyzed. The results show that the coupled flow is governed by the interaction of the bow vortex, deck-edge vortex, superstructure wake vortex, and rotor-induced vortex, while wind direction changes their relative importance. Under headwind conditions, the fore-aft asymmetry is most evident, and the maximum rotor-lift difference reaches approximately 25 kN, corresponding to a 17.6% reduction for the trailing helicopter due to the leading-helicopter wake and downwash. Spectral analysis shows dominant low-frequency components from 0.4 to 1.2 Hz, together with a persistent blade-passing frequency peak near 23.87 Hz. Under Green 30° and Red 30° winds, the dominant interference shifts toward the deck-edge vortex and leading-helicopter wake, producing more discrete multi-band spectral and coherence characteristics. Overall, inflow direction and deck position significantly affect dual-helicopter aerodynamic interference and should be considered in deck scheduling and safe operating limit assessment.