Actuator Surface Modeling of Rotors at the Ship–Helicopter Dynamic Interface

Abstract

The aerodynamics of the ship–helicopter dynamic interface play an important role in determining ship–helicopter operating limits. A review of prior studies, in conjunction with experimental work, indicates that a time-accurate rotor model and a physics-based turbulence-resolving flow solver with two-way coupling between these components are required to accurately predict rotor–airwake and rotor–rotor interactions. Here, a recently developed actuator surface model is validated against two further multirotor cases and employed for two large-scale ship–helicopter dynamic interfaces with up to three concurrent rotorcraft and five rotors. Simulations of the Sikorsky X2 rotor with significant rotor–rotor interaction match resolved unsteady rotor loading well using 1.2% of the computational effort of resolved blade calculations. Computations of the outwash from a Boeing CH-47D in hover gave results within experimental error bars for most azimuths, where discrepancies may be attributed to the estimated trim and division of rotor loading. Simulations of the dynamic interface between the Simple Frigate Shape 1 and a hovering UH-60a were presented for three wind-over-deck angles and three positions for 40 knots of wind speed. The computed thrust and root mean square thrust coefficients in the closed-loop pilot control band are presented and demonstrated to have an to have an expected dependence on immersion in the ship airwake. Finally, a large-scale dynamic interface computation was performed with two CH-47Ds and one UH-60a operating concurrently over the deck of the landing helicopter assault ship at 40 knots of wind speed and 0° and 30° angle. Results highlighted the importance of understanding rotor-wake/airwake interactions dependent on rotorcraft type and position and wind-over-deck. The computation provided unsteady thrust and torque for each of the five rotors from 60 s of data using just 11,424 central processing unit hours on a grid of 19.5×106 points. These simulations show that hybrid Navier–Stokes simulations employing actuator line or surface methods are capable of providing high-fidelity, time-accurate predictions of rotor loads at the ship–helicopter dynamic interface at substantially lower cost.