CFD-Trim 연계 해석 기법을 이용한 리프트 오프셋 동축반전 로터의 허브 효과 분석

초록

In this study, the effect of the hub on a high-speed lift-offset coaxial rotor is analyzed using KFLOW, an in-house code developed at Konkuk University. To investigate the hub effect at forward flight speeds of 150 knots and 200 knots, trim is performed under lift-offset conditions, and a CFD-Trim coupled analysis is conducted using CAMRAD II as the trim code. This approach reduced computational costs while ensuring high-accuracy trim results. At both 150 knots and 200 knots, the trim variable results exhibited similar trends regardless of the presence of the hub. Due to this similarity, the sectional normal force distributions were nearly identical in the azimuth range of 30° to 360°. However, differences is observed in the azimuth range of 0° to 30°. In the lower rotor, additional peaks appeared, or the peak magnitudes increased due to the influence of the downwash induced by the rotor when the hub was considered. Furthermore, in the upper rotor, the root-induced BVI(Blade-Vortex Interaction) exhibited different characteristics depending on the presence of the hub. When the hub was absent, the vortices generated at the root directly influenced the blades passing near the azimuthal angle of 10° without interacting with the hub. In contrast, when the hub was present, the root-generated vortices interacted with the hub before affecting the blades. Considering the hub better reflects the actual physical phenomena, and it is essential to include the hub in CFD analysis of coaxial rotor in forward flight.

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