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A three-dimensional compressible Navier-Stokes solver, KFLOW, using overlapped grids has recently been developed to simulate unsteady flow phenomena over helicopter rotor blades. The blade-vortex interaction is predicted for a descending flight using measured blade deformation data. The effects of computational grid resolution and azimuth angle increments on airloads were examined, and computed airloads and vortex trajectories were compared with HART-II wind tunnel data. The current method predicts the BVI phenomena of blade airloads reasonably well. It is found from the present study that a peculiar distribution of vorticity of tip vortices in an approximate azimuth angle range of 90 to 180 degrees can be explained by physics of the shear-layer interaction as well as the dissipation of numerical schemes.

A loose coupling approach is used to combine a comprehensive structural dynamics code CAMRAD II and a computational fluid dynamics solver KFLOW to validate the data and to identify the effect of fuselage on the aeroelastic behavior of the second higher harmonic rotor acoustic test rotor. The computations are made using isolated rotor and rotor-fuselage models. To demonstrate the effect of a fuselage, the shaft tilt angles remain identical for both configurations. A good correlation has been obtained with the present computational fluid dynamics/ comprehensive structural dynamics method. It is observed that a rotor-fuselage model improves the correlation significantly in terms of magnitudes and phases of the airloads solution. All the blade-vortex interaction peaks are captured accurately, and the phase shift in the section normal forces improves significantly, with the inclusion of a fuselage. The sources of improvements are investigated, considering the vorticity distributions and induced velocity fields of a rotor. It is revealed that the upwash pattern due to a fuselage is not restricted locally but propagates to considerable portions of the disk. Numerical results indicate that the upwash is responsible to lift up vortices at the zone of interest for a reduced miss distance, which results in a stronger blade-vortex interaction for improved correlations. Nomenclature= hub-based Cartesian coordinates α s = shaft tilt angle θ 0 , θ 1c , θ 1s = control pitch angles μ = advance ratio σ = solidity ψ = rotor azimuth angle Ω = rotor rotational speed

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