전단면 식생된 개수로 흐름에서 주흐름방향 渦 구조의 수치모의 = Numerical Investigations of Streamwise Vortical Structures in Fully Vegetated Open-Channel Flows

국문 초록 (Abstract)

본 연구에서는 전단면 식생된 개수로 흐름에서 발생되는 주흐름방향 渦 구조를 수치모의 하였다. 지배방정식에서의 난류 폐합을 위하여 레이놀즈응력 모형을 이용하였으며, 수로 폭-수심비 및 식생 밀도 조건에 따른 다양한 수치모의를 수행하였다. 그 결과 전단면 식생된 수로에서 횡방향으로 부수로가 형성되는 것을 확인하였으며, 이로 인해 주흐름방향 평균유속이 횡방향으로 파동의 형태를 취하는 것으로 나타났다. 또한 바닥 渦에 의해 자유수면과 측벽의 교차점 근처에서 최대유속이 수면 아래에 놓이는 유속경사역전 현상이 형성되는 것을 확인하였다. 이와 같은 횡방향 불균질성은 식생밀도가 증가함에 따라 더욱 뚜렷이 나타났다. 그러나 식생밀도가 1.0 m？¹ 이상이 될 경우 오히려 횡방향 불균질성은 감소되어 흐름구조가 횡방향으로 거의 균일해 지는 것을 확인하였다. 또한 수심 적분된 운동량 방정식으로부터 횡방향으로의 운동량 전달을 살펴보고 바닥 전단응력을 계산한 결과 이차흐름의 영향은 측벽 근처에서 바닥 전단응력을 증가시키는 반면에 횡방향 레이놀즈응력은 바닥 전단응력을 감소시키는 역할을 하는 것으로 나타났다.

다국어 초록 (Multilingual Abstract)

This paper presents a numerical investigation of the streamwise vortical structures in fully vegetated open-channel flows. The Reynolds stress model is used for the turbulence closure. Open-channel flows with various aspect ratios and vegetation densities are simulated. The computed vectors show the lateral subchannels, which results in wavy isovels of stream wise mean velocity. The velocity dip phenomenon due to the bottom vortex is clearly observed near the juncture between the free surface and the sidewall. This lateral heterogeneity is pronounced as the vegetation density increases. However, when the vegetation density exceeds a critical value of a = 1.0 m？¹, the lateral heterogeneity is weakened and the lateral flow structures become almost uniform. A depth-averaged analysis of the streamwise momentum equation is also performed to investigate the lateral momentum transfer. It is found that the component of secondary currents increases the bottom shear stress near the sidewall, while the component of lateral Reynolds stress decreases the bottom shear stress.

목차 (Table of Contents)

• Abstract
• 요지
• 1. 서론
• 2. 지배방정식
• 3. 폭-수심비의 영향
• 4. 식생밀도의 영향
• 5. 결론
• 감사의 글
• 참고문헌

참고문헌 (Reference)

1 "식생된 개수로에서 항력가중계수가 흐름에 미치는 영향 분석" 대한토목학회 26 (26): 529-537, 2006

2 "도시하천의 생태 수리 해석 및 복원기술" 건설교통부 2006

3 "Turbulent structures in partly vegetated open-channel flows with LDA and PIV measurements" 39 (39): 629-642, 2001

4 "Turbulence modeling of compound open-channel flows with and without vegetated floodplains using the Reynolds stress model" 29 (29): 1650-1664, 2006b

5 "Turbulence in plant canopies" 32 : 519-571, 2000

6 "Three dimensional turbulent structure in straight open-channel flows Journal of Hydraulic Research" 149-173, 1989

7 "The origin of secondary flow in turbulent flow along a corner Journal of Fluid Mechanics" 1-25, 1973

8 "Space-time correlation structures of horizontal coherent vortices in compound open-channel flows by using particle-tracking velocimetry" 35 (35): 191-208, 1997

9 "Reynolds stress modeling of vegetated open-channel flows" IAHR 42 (42): 3-11, 2004

10 "Reynolds stress modeling of rectangular open channel flows" 51 (51): 1319-1334, 2006a

11 "Reduced mixing in a marine macrophyte canopy" 305-309, 1993

12 "On some aspects of fully developed turbulent flow in rectangular channels Journal of Fluid Mechanics" 1965

13 "Numerical investigations of mean flow and turbulence structures of partly vegetated open channel flows using the Reynolds stress model" IAHR 44 (44): 203-217, 2006

14 "Modeling the pressure strain correlation of turbulence Journal of Fluid Mechanics" 245-272, 1991

15 "Mixing layers and coherent structures in vegetated aquatic flows" 107 (107): 2002

16 "Mass transport in vegetated shear flows" 5 : 527-551, 2005

17 "Large eddy simulation of free surface turbulent flow in partly vegetated open-channels" 39 : 919-937, 2002

18 "Hydrodynamic behavior of partly vegetated open channels" 122 (122): 625-633, 1996

19 "Ground effects on pressure fluctuations in the atmospheric boundary layer Journal of Fluid Mechanics" 491-511, 1978

20 "Flow over flexible vegetation and 3D structure of organized vortex associated with honami" 515 (515): 33-31 43, 1995

21 "Coherent eddies and turbulence in vegetation canopies: The mixing layer analogy" 78 : 351-382, 1996

22 "Cellular secondary currents in straight conduit Journal of Hydraulic Engineering" 173-193, 1984

23 "Annual Review of Fluid Mechanics" 365-424, 1984

24 "A survey of mean turbulent field closure" 590-599, 1973

25 "A preliminary numerical study of atmospheric turbulent flow in the idealized planetary boundary layer Journal of Atmospheric Science" 1327-1339, 1973

26 "A Reynolds stress model of turbulence and its application to thin shear flows Journal of Fluid Mechanics" 609-638, 1972