논문 상세보기
pp.213-223
본 연구에서는 bluff body의 공기역학적 진동현상들에 대한 칼만와류(Karman vortex)의 간섭 현상를 이해하기 위해서 구조적 기본단면인 사각단면(B/D=0.3~15)을 대상으로 정적공기력계수와 플러터계수를 일련의 정적실험과 강제가진실험을 통하여 구하였다. 실험에서는 splitter plate를 단면 후류부에 삽입함으로써 칼만와류의 방출을 억제, 칼만와류로부터 간섭받지 않는 상태의 주위유동 특성을 파악할 수 있었다. 또한 splitter Plate의 유무에 따른 실험결과의 비교연구는 이전에 발표된 다른 연구결과들과 잘 일치했으며 특히 갤로핑현상과 관련된 준정상이론에 근거한 dCL/dα의 변화와 H1 *의 변화를 중심으로 bluff body 주위의 흐름내에서 칼만와류의 간섭을 파악하였다. 결론적으로 B/D=3,4 단면에서 시간평균 적으로 단면 측면에 재부착하던 흐름이 splitter plate의 삽입으로 칼만와류의 방출을 억제하면 전연에서 박리한 흐름이 재부착하지 않음으로써 갤로핑현상이 관찰되었다. 즉 칼만와류의 억제는 전단박리층의 곡율을 늘임으로써 재부착점을 연장시키는 것으로 판단된다.
In this study, a series of wind tunnel tests were carried out to understand the complicated bluff body aerodynamics affected by Karman vortex on 2D rectangular cylinders with various side ratios, B/D=0.3~15. Based upon the aerostatic coefficients and aerodynamic derivatives of rectangular cylinders measured from experiments, the effects of the Karman vortex on the bluff body aerodynamics, especially paying attention to the galloping instability, are investigated. For mitigation of Karman vortex, a splitter plate with suitable size was installed in a wake center. By the installation of a splitter plate, the sharp peak in CD-B/D (B: along-wind length, D: cross-flow length) diagrams of stationary drag force was completely disappeared. Also, the value of dCL/dα(0°) was significantly sensitive to the Karman vortex, in particular, even its sign was changed in the range of B/D=0.6 to B/D=0.7 and B/D=3.0 to B/D=4.0, which means the marked role of the Karman vortex on the galloping instability based upon the quasi-steady theory. Furthermore, the flutter derivatives were also drastically affected by Karman vortex in the rather wide range of reduced velocity. In summary, it is considered that the substantial bluff body flow, which is not affected by Karman vortex, can be characterized by the side ratio of cylinders, and the interference of the Karman vortex on the fundamental flow depends on the side ratios of cylinders.
요 약
I. INTRODUCTION
II. EXPERIMENTAL APPARATUS
III. AEROSTATIC FORCE CHARACTERISTICS
IV. AERODYNAMIC DERIVATIVES& GALLOPING INSTABILITY
V. CONCLUSION
REFERENCE
