Skin Friction Predictions Over a Hovering Tilt-Rotor Blade Using OVERFLOW2

Skin friction predictions on hovering XV-15 helicopter blades have been made with the OVERFLOW2 flow solver using the Spalart-Allmaras turbulence model. The Figure of Merit (FM) at the 10-degree collective pitch is predicted reasonably and that at the 3-degree collective pitch is slightly under-predicted in comparison with experimental data. The trend in the skin friction predictions at the 10-degree collective pitch in the fully turbulent region is in reasonable agreement with the experimental data at radial stations removed from the root. At the 3-degree collective pitch the agreement in the fully turbulent region is about the same as in the 10-degree case. In the transition region, however, the predictions deviate significantly from the experimental data. By modulating the turbulence viscosity ap rioriin the experimentally known transition zone in various ways, OVERFLOW2 predicted a measurable change in the behavior of skin friction over the blade, especially in the transition region. This change was observed to be significant for the 3-degree collective pitch.

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