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이중 삼각날개의 스트레이크 형상에 따른 와류유동 상호작용 연구
정형석,정형석,이승현 한국물리학회 2019 새물리 Vol.69 No.7
고 받음각(angle of attack) 상황에서 안정성 증가는 날개 형상을 설계하는데 있어서 중요한 요소 중하나다. 이중 삼각날개 형상의 전투기에서는 스트레이크(strake)와 주 날개에서 발생하는 와류(vortex) 가 같은 방향으로 회전하면서 합쳐지게 된다. 이로부터 강력한 와류가 형성되어 공기흐름 분리지점을뒤쪽으로 후퇴시켜 양력을 증가시키는 효과가 발생한다. 그러나 일정 받음각 이상에서는 높은 회전속도로인하여 와류 구조가 급격히 깨져버리는 와류 붕괴(vortex breakdown) 현상이 가속화된다. 본 연구에서는스트레이크의 형상 변화가 삼각날개의 와류 상호작용과 와류 붕괴 특성에 어떤 영향을 미치는지를 규명하기 위해 일반적인 스트레이크 형상과 역방향 스트레이크 삼각날개 모델에 대한 풍동실험과 전산해석을비교하였다. 서로 반대방향으로 회전하는 와류 쌍을 발생시킬 수 있는 역방향 스트레이크 형상의 경우와류 상호작용과 병합과정이 가속되며 높은 받음각 영역에서 와류 붕괴현상을 지연시켜 이중 삼각날개의공력 특성 및 안정성 향상할 수 있음을 관찰하였다. Maintaining flight stability at higher angles of attack is one of the crucial factors in designing modern fighter aircraft. Conventional fighters usually generate two co-rotating vortices, are from the main wing and the after from the strake. These vortex systems merge into a strong vortex as they travel aft, generating beneficial effects such as lift augmentation. However, the merged vortex is more susceptible to vortex breakdown due to its higher rotational velocity, which deteriorates the aircraft performance. This paper investigates the effects of the strake shape on the vortex interaction and the vortex breakdown phenomenon. Both wind tunnel tests and computational analyses were carried out for a conventional strake delta wing and a reversed strake delta configuration, which can generate a counter-rotating vortex pair. The results indicate that the counter-rotating vortex pair accelerates both the interaction and the merging process and delays the vortex breakdown at higher angles of attack. We found that the aerodynamic characteristics and stability performance could be significantly improved by utilizing the variable strake-shape concept.
Unique Imaging Features of Spinal Neurenteric Cyst
정형석,박상민,김강언,김미경,송광섭 대한정형외과학회 2015 Clinics in Orthopedic Surgery Vol.7 No.4
A 50-year-old male presented with acutely progressed paraplegia. His magnetic resonance imaging demonstrated two welldemarcated components with opposite signals in one cystic lesion between the T1- and T2-weighted images at the T1 spine level. The patient showed immediately improved neurological symptoms after surgical intervention and the histopathological exam was compatible with a neurenteric cyst. On operation, two different viscous drainages from the cyst were confirmed. A unique similarity of image findings was found from a review of the pertinent literature. The common findings of spinal neurenteric cyst include an isointense or mildly hyperintense signal relative to cerebrospinal fluid for both T1- and T2-weighted images. However, albeit rarer, the signals of some part of the cyst could change into brightly hyperintensity on T1-weighted images and hypointensity on T2-weighted images due to the differing sedimentation of the more viscous contents in the cyst.