Dual Solver Computational Modeling of Ship-Helicopter Dynamic Interface Aeromechanics

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Moushegian, Alex Michael
Smith, Marilyn J.
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Shipboard landings are a fundamental capability of naval aircraft operations and present a unique challenge to helicopter pilots due to the complex aerodynamic interactions between the ship airwake and the helicopter aerodynamics, known as the dynamic interface (DI). As such, detailed analysis and testing must be done to establish the range of safe conditions at which these maneuvers can be performed, as well as to train pilots to perform them. With the advancement of computational power in the last two to three decades, computational tools have been investigated as a way to supplement flight testing for characterization of the DI. Hybrid CFD techniques have been developed in recent years with the intent of reducing the cost of rotorcraft computational fluid dynamics (CFD) simulations through coupling of an unsteady Reynolds-averaged Navier-Stokes (uRANS) solver with various lower-order computational aerodynamic solvers. Particularly promising for DI applications is the hybrid uRANS/free-vortex wake methodology, which uses uRANS to compute the rotor wake in the near-field and a potential flow model in the far-field. This technique allows wake-body and wake-wake interactions in the DI to be modeled without the need for a highly resolved uRANS domain in the large region between the ship and the helicopter. This research describes the necessary improvements and extensions of a hybrid uRANS/free-wake solver, OVERFLOW-CHARM, required to accurately characterize DI aerodynamics. These improvements are demonstrated and validated on model problems which include fundamental physics of the DI. First, OVERFLOW-CHARM is applied to analysis of an integrated propulsion system where interactional aerodynamics influence the performance of both the propeller and the wing. Second, OVERFLOW-CHARM is applied to rotors in ground effect, where its capabilities are quantified at a range of rotor scales. This verifies that OVERFLOW-CHARM will be able to accurately capture the interaction of the rotor wake with the ship deck during shipboard landing simulations. Finally, OVERFLOW-CHARM simulations replicating a flight test of the UH-60L helicopter operating within the influence of a model LPD-17 hangar face are performed to investigate OVERFLOW-CHARM's capabilities at capturing low-speed object-induced recirculation (LOIDR) effects which impact helicopter performance in the DI.
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