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Numerical Analysis on the Turbulence Patterns in The Scour Hole at The Downstream of Bed Protection

하상보호공 직하류부 세굴공의 난류양상에 관한 수치해석적 연구

  • Lee, Jaelyong (Dept. of Civil and Environmental Engineering, Incheon National University) ;
  • Park, Sung Won (Dept. of Civil and Environmental Engineering, Incheon National University) ;
  • Yeom, Seongil (Dept. of Civil and Environmental Engineering, Incheon National University) ;
  • Ahn, Jungkyu (Dept. of Civil and Environmental Engineering, Incheon National University)
  • 이재룡 (인천대학교 건설환경공학부) ;
  • 박성원 (인천대학교 건설환경공학부) ;
  • 염성일 (인천대학교 건설환경공학부) ;
  • 안정규 (인천대학교 건설환경공학부)
  • Received : 2019.01.19
  • Accepted : 2019.05.03
  • Published : 2019.05.31

Abstract

Where hydraulic structures are to be installed over the entire width of a river or stream, usually a bed protection structure is to be installed. However, a local scour occurs in which the river bed downstream of the river protection system is eroded due to the influence of the upstream flow characteristics. This local scour is dominant in the flow and turbulence characteristics at the boundary of the flow direction and in the material of the bed materials, and may gradually become dangerous over time. Therefore, in this study, we compared the turbulence patterns in the local scour hole at the downstream of the river bed protection with the results of the analysis of the mobile bed experiment, and compared with the application of OpenFoam, a three dimensional numerical analysis model. The distribution of depth-averaged relative turbulence intensities along the flow direction was analyzed. In addition to this result, the stabilization of scour hole was compared with the bed shear stress and Shields parameter, and the results were compared by changing the initial turbulent flow conditions. From the results, it was confirmed that the maximum depth of generation of the three-stage was dominantly developed by the magnitude of depth-averaged relative turbulence intensity rather than the mean flow velocity. This result also suggests that design, construction or gate control are needed to control the depth-averaged relative turbulence intensities in order to reduce or prevent the local scour faults that may occur in the downstream part of the bed protection.

강이나 하천 폭 전체에 걸쳐 수리구조물을 설치하는 경우에는 대개 하상보호공을 설치한다. 하지만 하상보호공직하류부에 있는 하천하상이 상류부의 흐름영향으로 인해서 유실되는 국부세굴현상이 발생한다. 이와 같은 국부세굴은 흐름방향 경계지점의 흐름 및 난류특성과 하상토의 재질 등에 지배적이며, 시간의 경과에 따라서 점차적으로 위험할 수 있다. 따라서 본 연구에서는 이동상 모형실험을 통해 분석된 시간변화에 따른 하상보호공 하류부 국부세굴공 내부의 난류성분을 3차원 수치해석모형인 OpenFOAM의 적용결과와 비교하고 국부세굴공발달의 주요인자라고 알려져 있는 수심 적분된 상대난류강도 값의 흐름방향별 분포를 분석하였다. 또한 이 결과와 함께 하상전단응력 및 Shields parameter와 비교하여 세굴공의 안정화에 대하여 분석하였으며 추가적으로 초기 난류유입조건을 변화시켜 그 결과를 비교하였다. 그 결과 세굴공의 최대발생깊이는 유속의 크기보다는 오히려 수심 적분된 상대난류강도의 크기에 따라 지배적으로 발달하는 것을 확인하였다. 이와 같은 결과를 통해서 향후 하상보호공 하류부에서 발생 가능한 국부세굴공을 저감하거나 방지하기 위해서는 수심 적분된 상대난류강도를 조절할 수 있는 설계나 시공 혹은 수문조절이 필요할 것으로 사료된다.

Keywords

SHGSCZ_2019_v20n5_20_f0001.png 이미지

Fig. 1. Geometrical model setup and mesh grid (not to scale, case_Q35h144d12 and case_Q35h120d12 d50=1.2 mm)

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Fig. 2. The distribution of wall shear stress τ0 and depth-averaged relative turbulence intensities r0 along the flow direction (case_Q35h144d12)

SHGSCZ_2019_v20n5_20_f0003.png 이미지

Fig. 3. The distribution of wall shear stress τ0 and depth-averaged relative turbulence intensities r0 along the flow direction (case_Q35h120d12)

Table 1. Physical experiment conditions of scour test

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Table 2. The boundary conditions of the model

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