대한토목학회논문집 (KSCE Journal of Civil and Environmental Engineering Research)

  • 제26권5B호
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  • Pages.529-537
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  • 2006
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  • 1015-6348(pISSN)
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  • 2799-9629(eISSN)
대한토목학회 (Korean Society of Civil Engeneers)
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식생된 개수로에서 항력가중계수가 흐름에 미치는 영향 분석

Impact of Drag-Related Weighting Coefficients in Vegetated Open-Channel Flows

  • 강형식 (연세대학교 사회환경시스템공학부) ;
  • 최성욱 (연세대학교 사회환경시스템공학부)
  • 투고 : 2006.05.12
  • 심사 : 2006.08.07
  • 발행 : 2006.09.30
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초록

본 논문에서는 식생된 개수로 흐름의 수치모의에 필요한 항력가중계수의 영향을 분석하였다. 이를 위해 시간 및 공간 평균기법을 이용하여 식생된 개수로 흐름에서 레이놀즈응력의 수송방정식을 유도하였다. 그 결과 총 레이놀즈응력은 시간의 변동 성분에 의한 레이놀즈응력과 공간상의 변동 성분에 의한 레이놀즈응력의 합이며, 총 레이놀즈응력의 수송방정식을 수치모의하기 위한 항력가중계수의 값은 $C_{fk}$ = 1.0인 것으로 나타났다. 그러나 시간의 변동 성분에 의한 레이놀즈응력을 수치모의하기 위해서는 거의 영에 가까운 항력가중계수를 갖는 것으로 나타났다. 이는 과거의 수치모의 연구에서 항력가중계수의 값이 거의 영에 가까울 때 실험결과와 잘 일치했는지에 대한 중요한 이유이다. 즉, 공간상의 변동성분에 의한 레이놀즈응력의 값은 실험을 통해 측정하기 매우 어렵기 때문에 식생된 개수로 흐름에서 측정된 레이놀즈응력은 대부분 시간상의 변동성분에 의한 레이놀즈응력이기 때문이다. 또한 레이놀즈응력모형을 이용하여 항력가중계수에 따른 식생된 개수로 흐름을 수치모의하고 기존의 실험 결과와 비교하였다. 그 결과 평균유속과 레이놀즈응력의 경우 항력가중계수의 영향은 작은 것으로 나타났으나, 난류강도 분포에서는 항력가중계수의 영향이 매우 크게 발생하였다. 또한 총 레이놀즈응력과 시간의 변동성분에 의한 레이놀즈응력의 수송방정식에서 각 항의 수지분석을 통하여 항력가중계수가 난류강도에 미치는 영향을 분석하였다.

This paper investigates the impacts of the drag-related weighting coefficients on mean velocity and turbulence structures. The transport equations for the Reynolds stress of vegetated open-channel flows are derived by using the temporal- and horizontal-averaging scheme. It is found that the total Reynolds stress of vegetated open channel flows consists of the Reynolds stress due to temporally fluctuating velocities and the Reynolds stress due to spatially fluctuating velocities. The drag-related weighting coefficient $C_{fk}$ for the total Reynolds stress component is found to be unit, while the coefficient for the Reynolds stress due to temporally fluctuating velocities can be negligible. This is the reason why very small weighting coefficients in previous studies yield very good agreements with measured data. In other words, the Reynolds stress due to spatially fluctuating velocities remains still unknown, especially due to the large number of measuring locations. Through a developed Reynolds stress model, vegetated open-channel flows are simulated and compared with measured data from the literature. Comparisons reveal that the computed mean flow and Reynolds stress structures are hardly affected by the drag-related weighting coefficients. However, the computed turbulence intensity profiles are significant different with the drag-related weighting coefficients. A budget analysis of the transport equations for the Reynolds stress component is carried to investigate why turbulence intensity is affected by the drag-related weighting coefficients.

키워드

참고문헌

  1. 강형식, 최성욱(2002) 개수로 흐름에서 레이놀즈응력모형의 비교. 대한토목학회논문집, 대한토목학회, 제22권 제1-B호, pp. 21-32
  2. Burke, R.W. (1982) Free surface flow through salt march grass. Ph.D. Thesis, Massachusetts Institute of Technology, Woods Hole Oceanographic, Eoods Hole, Mass
  3. Burke, R.W. and Stolzenbach, K.D. (1983) Free surface flow through salt marsh grass. MIT-Sea Grant Report MITSG 83-16, Massachusetts Institute of Technology, Cambridge, Mass
  4. Dunn, C.J. (1996) Experimental determination of drag coefficients in open channel with simulated vegetation, M.S. Thesis, University of Illinois at Urbana-Champaign, Urbana, IL
  5. Fischer-Antze, T., Stoesser, T., Bates, P., and Olsen, N.R.B. (2001) 3D numerical modeling of open channel flow with submerged vegetation. Journal of Hydraulic Research, IAHR, Vol. 39, No. 3, pp. 303-310 https://doi.org/10.1080/00221680109499833
  6. Gibson, M.M. and Launder, B.E. (1978) Ground effects on pressure fluctuations in the atmospheric boundary layer. Journal of Fluid Mechanics, Vol. 86, pp. 491-511 https://doi.org/10.1017/S0022112078001251
  7. Grega, L.M., Wei, T., Leighton, R.I., and Nevens, J.C. (1995) Turbulent mixed boundary flow in a corner formed by a solid wall and a free surface. Journal of Fluid Mechanics, Vol. 294, pp. 17-46 https://doi.org/10.1017/S0022112095002795
  8. Hanjalic, K. and Launder, B.E. (1972) A Reynolds stress model of turbulence and its application to thin shear flows. Journal of Fluid Mechanics, Vol. 52, pp. 609-638 https://doi.org/10.1017/S002211207200268X
  9. Li, R.M. and Shen, H.W. (1973) Effect of tall vegetations on flow and sediment. Journal of the Hydraulic Division, ASCE, Vol. 99, No. HY5, pp. 793-814
  10. Lopez, F. and Garcia, M. (1997) Open-channel flow through simulated vegetation: Turbulence modeling and sediment transport. Wetlands Res. Program Tech. Rep. WRP-CP-10, Waterw. Exp. Stn., Vicksburg, MS
  11. Lopez, F. and Garcia, M. (2001) Mean flow and turbulence structure of open-channel flow through non-emergent vegetation. Journal of Hydraulic Engineering, ASCE, Vol. 127, No. 5, pp. 392-402 https://doi.org/10.1061/(ASCE)0733-9429(2001)127:5(392)
  12. Mellor, G.L. and Herring, H.J. (1973) A survey of mean turbulent field closure. AIAA Journal, Vol. 11, pp. 590-599 https://doi.org/10.2514/3.6803
  13. Naot, D. and Rodi, W. (1982) Calculation of secondary currents in channel flow. Journal of the Hydraulics Division, ASCE, Vol. 108, No. HY8, pp. 948-968
  14. Mulhearn, P.J. (1978) Turbulent flow over a periodic rough surface. Physics of Fluids, Vol. 21, pp. 1113-1115 https://doi.org/10.1063/1.862350
  15. Neary, V.S. (2003) Numerical solution of fully developed flow with vegetative resistance. Journal of Engineering Mechanics, ASCE, Vol. 129, No. 5, pp. 558-563 https://doi.org/10.1061/(ASCE)0733-9399(2003)129:5(558)
  16. Nepf, H.M. (1999) Drag, turbulence, and diffusion in flow through emergent vegetation. Water Resources Research, AGU, Vol. 35, No. 2, pp. 479-489 https://doi.org/10.1029/1998WR900069
  17. Raupach, M.R., Coppin, P.A., and Legg, B.J. (1985) Experiments on scalar dispersion within a model plant canopy. Part I: the turbulence structure. Boundary-Layer Meteorology, Vol. 35, pp. 21-52 https://doi.org/10.1007/BF00117300
  18. Raupach, M.R. and Shaw, R.H. (1982) Averaging procedures for flow within vegetation canopies. Boundary Layer Meteorology, Vol. 44, No. 1, pp. 1-25 https://doi.org/10.1007/BF00117290
  19. Raupach, M.R. and Thorn, A.S. and Edwards, I. (1980) A wind tunnel study of turbulent flow close to regularly arrayed rough surfaces. Boundary-Layer Meteorology. Vol. 18, pp. 373-397 https://doi.org/10.1007/BF00119495
  20. Shimizu, Y. and Tsujimoto, T. (1993) Comparison of flood flow structure between compound channel and channel with vegetation zone. Proceedings of 25th IAHR Congress, Delft, The Netherlands
  21. Shimizu, Y. and Tsujimoto, T. (1994) Numerical analysis of turbulent open-channel flow over a vegetation layer using a k-e turbulence model. Journal of Hydroscience and Hydraulic Engineering, JSCE, Vol. 11, No. 2, pp. 57-67
  22. Shir, C.C. (1973) A preliminary numerical study of atmospheric turbulent flow in the idealized planetary boundary layer. Journal of Atmospheric Science, Vol. 30, pp. 1327-1339 https://doi.org/10.1175/1520-0469(1973)030<1327:APNSOA>2.0.CO;2
  23. Speziale, C.G., Sarkar, S., and Gatski, T. (1991) Modeling the pressure strain correlation of turbulence: an invariant dynamical systems approach. Journal of Fluid Mechanics, Vol. 227, pp. 245-272 https://doi.org/10.1017/S0022112091000101
  24. Tsujimoto, T., Kitamura, t, and Okada, T. (1991) Turbulent structure of flow over rigid vegetation covered bed in open-channels. KHL Progressive Report I, Hydr. Lab., Kanazawa Univ. Japan