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학술연구/단체지원/교육 등 연구자 활동을 지속하도록 DBpia가 지원하고 있어요.
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연구자들이 자신의 연구와 전문성을 널리 알리고, 새로운 협력의 기회를 만들 수 있는 네트워킹 공간이에요.
논문 기본 정보
- 자료유형
- 학술저널
- 저자정보
- 발행연도
- 2003.8
- 수록면
- 1,023 - 1,032 (10page)
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The effect of local forcing on the separated flow over a backward-facing step is investigated through hotwire measurements and flow visualization with multi-smoke wires. The boundary layer upstream of the separation point is laminar and the Reynolds number based on the free stream velocity and the step height is 13800. The local forcing is given from a slit located at the step edge and the forcing signal is always defined when the wind tunnel is in operation. In case of single frequency forcing, the streamwise velocity and the reattachment length are measured under forcing with various forcing frequencies. For the range of
0.010<St^θ<0.013, the forcing frequency component of the streamwise velocity fluctuation grows exponentially and is saturated at χ/h =0.75, while its subharmonic component grows following the fundamental and is saturated at χ/h=2.0. However, the saturated value of the subharmonic is much lower than that of the fundamental. It is observed that the vortex formation is inhibited by the forcing at Stθ = 0.019. For double frequency forcing, natural instability frequency is adopted as a fundamental frequency and its subharmonic is superposed on it. The fundamental frequency component of the streamwise velocity grows exponentially and is saturated at 0.5 < χ/h < 0.75, while its subharmonic component grows following the fundamental and is saturated at χ/h = 1.5 . Furthermore, the saturated value of the subharmonic component is much higher than that for the single frequency forcing and is nearly the same or higher than that of the fundamental. It is observed that the subharmonic component does not grow for the narrow range of the initial phase difference. This means that there is a range of the initial phase difference where the vortex pairing cannot be enhanced or amplified by double frequency forcing. In addition, this effect of the initial phase difference on the development of the shear layer and the distribution of the reattachment length shows a similar trend. From these observations, it can be inferred that the development of the shear layer and the reattachment length are closely related to the vortex paring.
0.010<St^θ<0.013, the forcing frequency component of the streamwise velocity fluctuation grows exponentially and is saturated at χ/h =0.75, while its subharmonic component grows following the fundamental and is saturated at χ/h=2.0. However, the saturated value of the subharmonic is much lower than that of the fundamental. It is observed that the vortex formation is inhibited by the forcing at Stθ = 0.019. For double frequency forcing, natural instability frequency is adopted as a fundamental frequency and its subharmonic is superposed on it. The fundamental frequency component of the streamwise velocity grows exponentially and is saturated at 0.5 < χ/h < 0.75, while its subharmonic component grows following the fundamental and is saturated at χ/h = 1.5 . Furthermore, the saturated value of the subharmonic component is much higher than that for the single frequency forcing and is nearly the same or higher than that of the fundamental. It is observed that the subharmonic component does not grow for the narrow range of the initial phase difference. This means that there is a range of the initial phase difference where the vortex pairing cannot be enhanced or amplified by double frequency forcing. In addition, this effect of the initial phase difference on the development of the shear layer and the distribution of the reattachment length shows a similar trend. From these observations, it can be inferred that the development of the shear layer and the reattachment length are closely related to the vortex paring.
목차
Abstract
1.서론
2.실험장치 및 방법
3.실험결과
4.결론
후기
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