Dynamic response of a helicopter hovering above a ship’s flight deck*

We present a CFD study of a helicopter hovering 9 m above the flight deck of the full-scale ONR Tumblehome ship. Regular head waves for sea states 3 and 6 are analyzed with wind speeds of 15 and 35 knots, respectively, while the ship advances at 15 knots. Two approaches are used. In one-way coupling the water and air flow, and ship motion are predicted without the rotorcraft, while independent performance curves of a generic 4-bladed rotor based on the SH-60 Seahawk are computed. Then the thrust on the rotor is computed for large and small helicopters (SH-60 and Robinson R22 sizes) and a small drone (0.75 m rotor diameter). Small scale turbulent fluctuations are mostly filtered by the larger craft, but the drone is strongly affected by small scales. The response to the wave encounter frequency is considerable for all cases. A two-way analysis was performed for SH-60, computing air/water flow and motion in waves maintaining the helicopter (with rotating main and tail rotors) at constant altitude. Baseline cases with no ship motions and of the helicopter were also computed. The thrust shows a strong peak at the blade passing and wave encounter frequency and harmonics.