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RISS 인기검색어
- 검색키워드
- 주제어 : Turbulent Coherent Structures (난류응집구조) (검색결과 5 건)
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오상호(Oh, Sang-Ho),서경덕(Suh, Kyung-Duck),水谷夏樹(Natsuki Mizutani) 한국해안해양공학회 2007 한국해안해양공학회 논문집 Vol.19 No.1
이 연구에서는 심해 풍파 아래에서의 응집구조(coherent structures)에 대한 실험실 실험 결과를 제시하였다. 풍속과 취송거리가 서로 다른 실험 조건에서 입자화상유속계를 이용하여 취득된 심해 풍파의 속도장으로부터 와도장을 가시화하고 응집구조가 시 공간적으로 변천하는 양상 및 그에 따른 와도의 연직 분포 변화를 정성적으로 분석하였다. 파봉 아래에서는 파와 같은 위상으로 함께 진행하는 응집구조가 존재함을 확인하였다. 이 응집구조의 회전 방향은 바람이 10 m/s 이하인 실험 조건에서는 파 내부의 입자 궤도 운동과 반대 방향인 반면, 바람의 세기가 약 13 m/s이고 파봉 근처에서 쇄파가 발생하는 경우에는 같은 방향이었다. 수면 근처에서는 응집구조의 진행에 따른 복잡한 소용돌이 상호 작용이 나타나는 반면, 수면으로부터 깊은 수심에서는 파 궤도 운동의 영향이 미미하여 응집구조의 시 공간적 변화가 거의 없었다. The results of experimental investigation of coherent structures beneath wind-generated waves in deep water are presented. Vorticity fields of deepwater wind waves were visualized by analyzing the velocity fields obtained by PIV measurements under different wind and fetch conditions. In addition, spatio-temporal evolution of the coherent structures and subsequent changes in vertical profiles of the instantaneous vorticity were qualitatively examined. It was found that a coherent structure is formed right underneath the wave crest and traveled in phase with the surface wave. The direction of rotation of the coherent structure was contrary to the wave orbital motion when wind speed is less than 10 m/s, while was same as the wave orbital motion when wind speed is approximately 13 m/s and wave breaking occurs at the wave crest. In the near-surface region, complex vortex-vortex interactions were observed according to the traveling of the coherent structure. In contrast, coherent structures far below the water surface changed little due to weak influence of orbital motion by the surface waves.
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응집구조 추출기법을 이용한 전방 계단에서의 난류 소음 원인 분해
조문환(Munhwan Cho),배영민(Young Min Bae),문영준(Young J. Moom) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
The flow structures and acoustic sources are identified by coherent structure identification methods for the turbulent forward-facing step flow at Re<SUB>h</SUB>=8,000 [AIAA paper 2005-3006, S. Becker et al., 2005]. The identification methods like proper orthogonal decomposition (POD) and its complement method with others are applied to the turbulent flow and acoustic field, which are able to decompose the properties into each mode that has its own characteristics and energy level. These methods are not only to study the random fluctuated hydrodynamic and acoustic properties but also to extract the relation between the turbulent flow structures and the acoustic sources.
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이재화(Jae Hwa Lee) 한국가시화정보학회 2014 한국가시화정보학회지 Vol.12 No.3
Direct numerical simulation (DNS) dataset of a turbulent boundary layer (TBL) with a step change from smooth to rough surface is analyzed to examine spatially developing flow characteristics. The roughness elements are periodically arranged two-dimensional (2-D) spanwise rods with a streamwise pitch of λ = 8k (= 12θin), and the roughness height is k = 1.5θin, where θin is the inlet momentum thickness. The step change is introduced 80θin downstream from the inlet. For the first time, full images from the DNS data with the step change from the smooth to rough walls is present to get some idea of the geometry of turbulent coherent structures over rough wall, especially focusing on their existence and partial dynamics over the rough wall. The results show predominance of hairpin vortices over the rough wall and their spanwise scale growth mechanism by merging.
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압력변동 및 속도장 조건부 평균에 의한 후향계단 유동의 응집구조
이인원(Inwon Lee),성형진(Hyung-Jin Sung),이인섭(In-Seop Lee) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.9
Time-dependent characteristics of wall pressure fluctuations in separated and reattaching flows over a backward-facing step were investigated by means of continuous wavelet transform. Emphasis was placed on the combination of time-localized analyses of wavelet transform and multi-point measurements of pressure fluctuations. Synchronized wavelet maps revealed the evolutionary behavior of pressure fluctuations and gave further insight into the modulated nature of large-scale vortical structures. It was found that there exist two modes of shed vortices: one is the global oscillation and the other is the vortex convection. The two alternating modes are synchronized with the flapping frequency component of pressure fluctuations. Toward the investigation of the direct relationship between the flow field and the relevant spatial mode of the pressure field, a new kind of wavenumber filtering of pressure distribution, termed as a spatial box filter (SBF), is introduced and examined.
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