Numerical Investigation of Unsteady Airloads for a Helicopter Hovering over a Ship Flight Deck

A CFD-based constrained three-component aerodynamic-trim procedure is implemented to investigate the load balance and coupled flowfield response of a simplified shipborne helicopter hovering over a flight deck. During the unsteady CFD calculation, the collective and cyclic pitch controls are updated according to the period-averaged vertical force and the rolling and pitching moments of the helicopter center of gravity. A pre-trim initialization is introduced before the formal-trim process to avoid large pitch corrections from the initial fixed-pitch state. Under a 20 m/s headwind, the initial fixed-pitch case shows a vertical-force deficit and extra rolling and pitching moments. After dynamic trim, the pitch controls converge to θ0=8.46°, A1=−2.48°, and B1=1.20°. Over the final one-revolution interval of approximately t = 31.74–32.00 s, the period-averaged loads are Fz=112.82 kN, Mx=−0.06 kN·m, and My=−0.07 kN·m. Additional +30° and −30° oblique-wind calculations confirm convergence toward the prescribed three-component load targets under asymmetric inflow conditions. The instantaneous flowfield comparisons suggest local responses in the rotor-inflow and fuselage-pressure regions after trim. Frequency-domain analysis identifies a dominant blade-passing-frequency component together with additional low-frequency content characteristic of the coupled rotor–ship aerodynamic response.