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Computational fluid dynamics simulations of ship airwake with a hovering helicopter rotor

Orbay, Ezgi
In this thesis, Computational Fluid Dynamic simulations of ship airwake for a simple ship geometry are performed for the horizontal and inclined deck configurations and also with and without the helicopter rotor over the deck. An actuator disk model is used for the CFD simulations of a rotor model hovering over the flight deck. All of the computations are performed by using a commercial finite volume CFD flow solver. The unstructured tetrahedral grids are generated in the computational domain including ship geometry and rotor disk. The flow around the Simple Frigate Shape 2 (SFS2) ship geometry is computed by solving RANS and hybrid RANS/LES equations. The steady-state and unsteady computations with different turbulence models are performed. A good validation is obtained with the hybrid RANS/LES turbulence model. After the validation study for the simulation results with the standard (horizontal) model, ship motion due to sea waves is discussed and only an instant of the roll motion is considered as an inclined flight deck problem and investigated. Therefore, a 10 degree rotation about x-axis is given to ship geometry, which illustrates roll motion of ship in rough sea conditions. Comparisons of the results with horizontal (un-inclined) and inclined deck cases are done. Also, a rotor disk with zonal boundary conditions is used with both horizontal and inclined ship models to investigate downwash effect of rotor on ship airwake. Full-scale, four-bladed S-76 helicopter rotor is selected as the rotor model. Rotor only case is first solved and validated with the available wind tunnel data. Then, steady-state simulations for ship with rotor cases are performed. In this part of the study, the effect of ship airwake on rotor performance was not considered, only the effect of hovering rotor wake (downwash) on the ship airwake was taken into account. Flow around the inclined ship deck is observed as different from the horizontal deck. When a rotor is also included over the deck, the flow features such as vortical structures and vertical velocity magnitudes are changed showing that the interactions is more complicated to accurately model and solve.