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Rotor aerodynamics is governed by wake behavior. Particularly, aerodynamic performance in the hovering flight condition is determined by the structure and the strength of the wake. In this paper, rotating blades were simulated using a tightly coupled computational fluid dynamics and time-marching free-wake method in hovering and forward flight. The rotating blades and a flowfield near the rotor are calculated by the computational fluid dynamics, and the strength and motions of the wake are simulated with the time-marching free-wake method. A moving overset grid technique is applied to consider rotor motions during hovering and forward flight. Inflow and outflow conditions in the computational fluid dynamics domain are provided from an induced flow rate by the time-marching free-wake method at each time step. The strength of the trailed vortices is determined from a sectional lift calculated in the rotating blade, which is computed using the computational fluid dynamics. The present coupled method was compared with other inflow and outflow conditions, such as source-sink and Riemann-invariant conditions. To investigate the robustness of the present method, grid-size effects were also tested in large and small background grid systems. Nomenclature a = distance between velocity position and vortex filament a c = vortex core radius a 1 = speed of soundMach number, R=a 1 R = rotor radius r = spanwise distance along rotor y = wake node position = flapping angle = vortex circulation strength bound = bound vortex circulation strength trailed = trailed vortex circulation strength = pitch angle = azimuth angle

Rotor aerodynamics is governed by wake geometry and strength. However, rotor wake characteristics computed by the rotor computational fluid dynamics are not clearly described due to numerical dissipation. To overcome this numerical problem, free-wake is used for wake simulation. The present free-wake describes the inboard vortices as well as the tip vortices of the blade. At each time step, the free-wake provides inflow and outflow conditions of the boundary of the Eulerian domain, and the Euler solver is used for solving the flow field near the rotor blade. Finally, the coupled method is compared with the conventional method and the experimental results.

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