Aerodynamic interactions of the model NREL 5 MW offshore horizontal axis wind turbines (HAWT) are investigated using a highfidelity computational fluid dynamics (CFD) analysis. Four wind turbine configurations are considered; three-bladed upwind and downwind and two-bladed upwind and downwind configurations, which operate at two different rotor speeds of 12.1 and 16 RPM. In the present study, both steady and unsteady aerodynamic loads, such as the rotor torque, blade hub bending moment, and base the tower bending moment of the tower, are evaluated in detail to provide overall assessment of different wind turbine configurations. Aerodynamic interactions between the rotor and tower are analyzed, including the rotor wake development downstream. The computational analysis provides insight into aerodynamic performance of the upwind and downwind, two-and three-bladed horizontal axis wind turbines.

In the present study, the ducted fan hover performance is numerically investigated for Fan-In-Wing (FIW) applications using a high-fidelity unstructured grid Computational Fluid Dynamics (CFD) solver U 2 NCLE. Effects of the ducted fan geometric parameters such as the fan blade twist and the duct inlet lip radius are evaluated in details for the ducted fan hover efficiency and stall margin over a wide range of collective angles. Both open fans and ducted fans are investigated for their aerodynamic characteristics including the blade sectional loadings and the duct pressure distributions. The induced inflow velocity and the downwash wake profiles of the ducted fan systems are investigated under different fan blade twists, and the flow separation phenomena on the blade and duct surfaces are evaluated with different duct inlet profiles. Computational results indicate that the blade twist provides consistent effects on the Figure of Merit and the stall margin in both the open and ducted fans being studied, and the duct inlet profile has a significant impact on the overall hover performance of the ducted fan system. The numerical studies performed here provide better understanding of the aerodynamic interactions inside the ducted fans, and insight into the optimal aerodynamics design for the future FIW systems. Nomenclaturenumber of blades OF = open fan p = pressure P = fan power PL = power loading, / 1 Associate Professor, 2 Q = fan torque R = fan blade radius R lip = duct inlet lip radius RBF = radial basis function s/D = duct distance T = thrust y + = y plus value TPP = blade tip path plane V tip = blade tip velocity, Ω V z = induced velocity, axial velocity, downwash velocity ρ = density σ = blade solidity, / θ 75 = fan blade collective angle at 75% span φ = inflow angle Ω = fan rotational speed

CFD/CSD coupled simulations are presented for a Bell M427 main rotor in both forward and maneuvering flight. The unstructured CFD code U 2 NCLE is coupled with the CSD code DYMORE2.0 to perform rotor aeroelastic analysis. Two CFD/CSD coupling strategies are evaluated and demonstrated: loose coupling for rotors in a steady level forward flight and tight coupling for rotors undergoing a maneuver. A Fluid-Structure Interface (FSI) handles the information exchange and directs operation of the CFD and CSD codes required to perform tight coupling analysis. The loose coupling results are assessed with the forward flight test data, and the tight coupling method is verified by comparing to the results obtained with the loose coupling method in forward flight where fixed control settings are used. For a maneuvering flight, user-prescribed control variations drive the collective pitch angle to a ±2˚ doublet profile superimposed on the loose coupling control settings. The coupled simulations demonstrate the feasibility of performing aeromechanical analysis for realistic helicopter rotors.

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