All Issue

2018 Vol.5, Issue 4
December 2018. pp. 199-209
Abstract

In river design, consideration of bed shear stresses is necessary to secure stability of levee and floodplain. In this study distributions of bed shear stresses in compound open channels are analyzed through numerical simulation for various width and depth. LES solver in OpenFOAM is applied to 12 cases of compound channel shapes considering secondary flow which effects distributions of bed shear stresses. By the results time averaged velocity distributions, secondary currents, and distributions of bed shear stresses are analyzed. Overall distributions of bed shears in floodplain show that higher shear stresses are seen in left of floodplain and the shears decrease toward right of floodplain. However, high local variations in shear stresses are shown due to the secondary flow effects. In shallow floodplain, bed shear stresses show low value below 0.8 times of averaged bed shear. In deep floodplain, bed shear stresses show high value over 1.2 – 1.4 times of averaged bed

하천설계에서 제방과 홍수터의 안정성 확보를 위해서는 바닥전단응력을 고려하는 것이 필수적이다. 본 연구에서는 다양한 하폭과 수심에 따른 복단면의 바닥전단응력을 모의하여 분포 특성을 분석하였다. 바닥전단응력 분포에 지배적인 영향을 주는 이차류를 모의하기 위하여 OpenFOAM의 large eddy simulation (LES)를 적용하였으며 하폭과 수심을 고려하여 12개의 케이스를 모의하였다. 모의 결과를 이용하여 시간 평균 유속 분포, 이차류 분포, 바닥전단응력 분포 등의 특성에 대하여 분석하였다. 홍수터 바닥전단응력 분포는 전체적으로 홍수터 좌안에서 높은 값이 나타나고 우안 방향으로 감소하는 경향을 확인하였으나 이차류에 의해 상당한 국부적인 변화가 나타남을 확인하였다. 홍수터의 수심이 얕은 경우에는 홍수터의 바닥전단응력이 평균전단응력의 0.8배 이하로 낮은 값이 나타나고 있으나 홍수터의 수심이 깊은 경우에는 평균전단응력의 1.2-1.4배의 높은 값이 나타남을 확인하였다. 홍수터의 폭이 좁은 경우에는 홍수터 우안 측벽의 영향으로 국부적으로 높은 값이 나타나는 것도 확인할 수 있었다.

References
  1. Ban, C. and Choi, S.U. 2011. Large eddy simulation of rectangular open-channel flow using OpenFOAM. Journal of the Korean Society of Civil Engineers 34(3): 833-840.10.12652/Ksce.2014.34.3.0833
  2. Cater, J.E. and Williams, J.J.R. 2008. Large eddy simulation of a long asymmetric compound. Journal of Hydraulic Research 46(4): 445-453.10.3826/jhr.2008.3134
  3. Constantinescu, G., Sukhodolov, A. and McCoy, A. 2009. Mass exchange in a shallow channel flow with a series of groynes: LES study and comparison with laboratory and field experiments. Environmental Fluid Mechanics 9(6): 587.10.1007/s10652-009-9155-2
  4. Kara, S., Stoesser, T., and Sturm, T.W. 2012. Turbulence statistics in compound channels with deep and shallow overbank flows. Journal of Hydraulic Research, 50(5), 482-493, DOI: 10.1080/00221686.2012.724194.10.1080/00221686.2012.724194
  5. Lee, D. 2017. Analysis of compound open channel flow using Large Eddy Simulation (LES). Ecology and Resilient Infrastructure 4(1): 054-062.10.17820/eri.2017.4.1.054
  6. Naot, D., Nezu, I. and Nakagawa, H. 1993. Hydrodynamic behavior of compound rectangular open channels. Journal of Hydraulic Engineering 119(3): 390-408.10.1061/(ASCE)0733-9429(1993)119:3(390)
  7. Pezzinga, G. 1994. Velocity distribution in compound channel flows by numerical modeling. Journal of Hydraulic Engineering 120(10): 1176-1198.10.1061/(ASCE)0733-9429(1994)120:10(1176)
  8. Prinos, P., Townsend, R. and Tavoularis, S. 1985. Structure of turbulence in compound channel flows. Journal of Hydraulic Engineering 111(9): 1246-1261.10.1061/(ASCE)0733-9429(1985)111:9(1246)
  9. Rogallo, R.S. and Moin, P. 1984. Numerical simulation of turbulent flows. Annual Review of Fluid Mechanics 16(1): 99-137.10.1146/annurev.fl.16.010184.000531
  10. Shiono, K. and Knight, D.W. 1991. Turbulent open channel flows with variable depth across the channel. Journal of Fluid Mechanics 222: 617-646.10.1017/S0022112091001246
  11. Sofialidis, D. and Prinos, P. (1998). Compound open- channel flow modelling with nonlinear low-Reynolds k-e models. J. Hydraulic Eng., 124 (3): 253-262.10.1061/(ASCE)0733-9429(1998)124:3(253)
  12. Stoesser, T., Kim, S.J. and Diplas, P. 2010. Turbulent flow through idealized emergent vegetation. Journal of Hydraulic Engineering 136(12): 1003-1017.10.1061/(ASCE)HY.1943-7900.0000153
  13. Thomas, T.G. and Williams, J.J.R. 1995. Large eddy simulation of turbulent flow in an asymmetric compound open channel. Journal of Hydraulic Research 33(1): 27-41.10.1080/00221689509498682
  14. Tominaga, A. and Nezu, I. 1991. Turbulent structure in compound open-channel flows. Journal of Hydraulic Engineering 117(1): 21-41.10.1061/(ASCE)0733-9429(1991)117:1(21)
  15. Van Balen, W., Blanckaert, K. and Uijttewaal, W.S.J. 2010. Analysis of the role of turbulence in curved open-channel flow at different water depths by means of experiments, LES and RANS. Journal of Turbulence 11(12): 1-34.10.1080/14685241003789404
Information
  • Publisher :Korean Society of Ecology and Infrastructure Engineering
  • Publisher(Ko) :응용생태공학회
  • Journal Title :Ecology and Resilient Infrastructure
  • Journal Title(Ko) :응용생태공학회 논문집
  • Volume : 5
  • No :4
  • Pages :199-209
  • Received Date :2018. 10. 09
  • Accepted Date : 2018. 11. 28