紊动对黏性细颗粒泥沙絮凝沉降影响的试验研究
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摘要
利用室内环形水槽及高倍摄像设备,定量研究了不同悬沙浓度及紊动剪切对黏性细颗粒泥沙絮凝沉降特性的影响。试验中观测到的絮团粒径为分散颗粒的几倍到几十倍,絮团中值粒径随着水体紊动剪切的增大呈先增大后减小的变化趋势,最大的中值粒径约为150μm,出现在紊动剪切为30 1/s条件下。悬沙浓度的增大促进絮团的发育,在350 mg/L条件下形成的絮团整体粒径比150 mg/L条件下的更大。絮团中值沉降速度在0.7～3.4 mm/s之间,絮团最大的中值沉速出现在紊动强度最大时65 1/s,此时所形成的絮团结构密实,有效密度较大。絮团有效密度随着粒径的增大而减小,研究表明,采用变分形维数方法,对有效密度随粒径变化的模拟结果与试验结果吻合较好。
Influences of suspended load concentration and turbulent shear rate on flocculation and floc settling properties were studied by using annular flume and camera system. It was found that floc sizes were a few to a few ten times larger than primary particle size, and the median floc size increased at first, and then decreased with the increasing of turbulent shear rate. The maximum median floc size about 150 μm occurred under the shear rate of 30 1/s. The increase of suspended sediment concentration is benefit to the development of flocculation, with higher median floc size under higher concentration. The median floc settling velocity was in the range of 0.7～3.4 mm/s, and the maximum value was measured under the highest shear rate of 65 1/s, because flocs formed under this condition were denser. Floc effective density decreased with the increase of floc size, and the simulations using variable fractal dimension fit well with the experimental results.
Influences of suspended load concentration and turbulent shear rate on flocculation and floc settling properties were studied by using annular flume and camera system. It was found that floc sizes were a few to a few ten times larger than primary particle size, and the median floc size increased at first, and then decreased with the increasing of turbulent shear rate. The maximum median floc size about 150 μm occurred under the shear rate of 30 1/s. The increase of suspended sediment concentration is benefit to the development of flocculation, with higher median floc size under higher concentration. The median floc settling velocity was in the range of 0.7～3.4 mm/s, and the maximum value was measured under the highest shear rate of 65 1/s, because flocs formed under this condition were denser. Floc effective density decreased with the increase of floc size, and the simulations using variable fractal dimension fit well with the experimental results.
引文
[1] Winterwerp J C, Kesteren V W G M. Introduction to the physics of cohesive sediment dynamics in the marine environment [M]. 2004, Elsevier.
[2] Droppo, I G, Ongley E D. Flocculation of suspended sediment in rivers of southeastern Canada [J]. Water Research, 1994, 28(8): 1799-1809.
[3] Dyer K R. Sediment processes in estuaries: Future research requirements [J]. Journal of Geophysical Research Oceans, 1989, 94 (C10): 14327-14339.
[4] Chen S, Eisma D, Kalf J. In situ distribution of suspended matter during the tidal cycle in the elbe estuary [J]. Netherlands Journal of Sea Research, 1994, 32(1): 37-48.
[5] Uncles R J, Bale A J, Stephens J A, et al. Observations of floc sizes in a muddy estuary [J]. Estuarine, Coastal and Shelf Science, 2010, 87(2): 186-196.
[6] Fettweis M, Baeye M. Seasonal variation in concentration, size, and settling velocity of muddy marine flocs in the benthic boundary layer [J]. Journal of Geophysical Research: Ocean, 2015, 120(8): 5648-5667.
[7] Goldberg S, Forster H S, Heick E L. Flocculation of illite/kaolinite and illite/montmorillonite mixtures as affected by sodium adsorption ratio and ph [J]. Clays Clay Miner, 1991, 39(4): 375-380.
[8] 张志忠.长江口黏性泥沙基本特性研究[J].泥沙研究,1996(1):67-73.
[9] Manning A J, Dyer K R. A laboratory examination of floc characteristics with regard to turbulent shearing [J]. Marine Geology, 1999, 160(1): 147-170.
[10] Mietta F, Chassagne C, Manning A J, et al. Influence of shear rate, organic matter content, pH and salinity on mud flocculation [J]. Ocean Dynamic, 2009, 59(5): 751-763.
[11] Kumar R G, Strom K B, Keyvani A. Floc properties and settling velocity of San Jacinto estuary mud under variable shear and salinity conditions [J]. Continental Shelf Research, 2010, 30(20): 2067-2081.
[12] Winterwerp J C. A simple model for turbulence induced flocculation of cohesive sediment [J]. Journal of Hydraulic Research, 1998, 36(3): 309-326.
[13] Ferguson R I, Church M. A simple universal equation for grain settling velocity [J]. Journal of Sedimentary Research, 2004, 74 (6): 933-937.
[14] Guo C, He Q, Guo L, et al. A study of in-situ sediment flocculation in the turbidity maxima of the Yangtze Estuary [J]. Estuarine, Coastal and Shelf Science, 2017, 191: 1-9.
[15] Manning A J, Whitehouse R J S. UoP Mini-annular flume-operation and hydrodynamic calibration [R]. HR Wallingford Technical Report, 2009, TR 169.
[16] Manning A J, Baugh J V, Spearman J R, et al. Flocculation settling Characteristics of mud: Sand mixtures [J]. Ocean Dynamic, 2010, 60 (2): 237-253.
[17] Gratiot N, Manning A J. An experimental investigation of floc characteristics in a diffusive turbulent flow [J]. Journal of Coastal Research, 2004, 20 (1): 105-113.
[18] Dyer K R, Manning A J. Observation of the size, settling velocity and effective density of flocs, and their fractal dimensions [J]. Journal of Sea Research, 1999, 41(1-2): 87-95.
[19] Van Leussen W. The Kolmogorov microscale as a limiting value for the floc sizes of suspended fine-grained sediments in estuaries [M]. Burt N, Parker R, Waltls J [Eds]. Cohesive Sediments, America: Wiley, 1997: 45-62.
[20] Fennessy M J, Dyer K R, Huntley D A. An instrument to measure the size and settling velocity of flocs in situ [J]. Marine Geology, 1994, 117(1-4): 107-117.
[21] Kranenburg C. The fractal structure of cohesive sediment aggregates [J]. Estuarine, Coastal and Shelf Science, 1994, 39(6): 451-460.
[22] Maggi F, Mietta F, Winterwerp J C. Effect of variable fractal dimension on the floc size distribution of suspended cohesive sediment [J]. Journal of Hydrology, 2007, 343(1-2): 43-55.
[23] Khelifa A, Hill P S. Models for effective density and settling velocity of flocs [J]. Journal of Hydraulic Research, 2006, 44(3), 390-401.
[2] Droppo, I G, Ongley E D. Flocculation of suspended sediment in rivers of southeastern Canada [J]. Water Research, 1994, 28(8): 1799-1809.
[3] Dyer K R. Sediment processes in estuaries: Future research requirements [J]. Journal of Geophysical Research Oceans, 1989, 94 (C10): 14327-14339.
[4] Chen S, Eisma D, Kalf J. In situ distribution of suspended matter during the tidal cycle in the elbe estuary [J]. Netherlands Journal of Sea Research, 1994, 32(1): 37-48.
[5] Uncles R J, Bale A J, Stephens J A, et al. Observations of floc sizes in a muddy estuary [J]. Estuarine, Coastal and Shelf Science, 2010, 87(2): 186-196.
[6] Fettweis M, Baeye M. Seasonal variation in concentration, size, and settling velocity of muddy marine flocs in the benthic boundary layer [J]. Journal of Geophysical Research: Ocean, 2015, 120(8): 5648-5667.
[7] Goldberg S, Forster H S, Heick E L. Flocculation of illite/kaolinite and illite/montmorillonite mixtures as affected by sodium adsorption ratio and ph [J]. Clays Clay Miner, 1991, 39(4): 375-380.
[8] 张志忠.长江口黏性泥沙基本特性研究[J].泥沙研究,1996(1):67-73.
[9] Manning A J, Dyer K R. A laboratory examination of floc characteristics with regard to turbulent shearing [J]. Marine Geology, 1999, 160(1): 147-170.
[10] Mietta F, Chassagne C, Manning A J, et al. Influence of shear rate, organic matter content, pH and salinity on mud flocculation [J]. Ocean Dynamic, 2009, 59(5): 751-763.
[11] Kumar R G, Strom K B, Keyvani A. Floc properties and settling velocity of San Jacinto estuary mud under variable shear and salinity conditions [J]. Continental Shelf Research, 2010, 30(20): 2067-2081.
[12] Winterwerp J C. A simple model for turbulence induced flocculation of cohesive sediment [J]. Journal of Hydraulic Research, 1998, 36(3): 309-326.
[13] Ferguson R I, Church M. A simple universal equation for grain settling velocity [J]. Journal of Sedimentary Research, 2004, 74 (6): 933-937.
[14] Guo C, He Q, Guo L, et al. A study of in-situ sediment flocculation in the turbidity maxima of the Yangtze Estuary [J]. Estuarine, Coastal and Shelf Science, 2017, 191: 1-9.
[15] Manning A J, Whitehouse R J S. UoP Mini-annular flume-operation and hydrodynamic calibration [R]. HR Wallingford Technical Report, 2009, TR 169.
[16] Manning A J, Baugh J V, Spearman J R, et al. Flocculation settling Characteristics of mud: Sand mixtures [J]. Ocean Dynamic, 2010, 60 (2): 237-253.
[17] Gratiot N, Manning A J. An experimental investigation of floc characteristics in a diffusive turbulent flow [J]. Journal of Coastal Research, 2004, 20 (1): 105-113.
[18] Dyer K R, Manning A J. Observation of the size, settling velocity and effective density of flocs, and their fractal dimensions [J]. Journal of Sea Research, 1999, 41(1-2): 87-95.
[19] Van Leussen W. The Kolmogorov microscale as a limiting value for the floc sizes of suspended fine-grained sediments in estuaries [M]. Burt N, Parker R, Waltls J [Eds]. Cohesive Sediments, America: Wiley, 1997: 45-62.
[20] Fennessy M J, Dyer K R, Huntley D A. An instrument to measure the size and settling velocity of flocs in situ [J]. Marine Geology, 1994, 117(1-4): 107-117.
[21] Kranenburg C. The fractal structure of cohesive sediment aggregates [J]. Estuarine, Coastal and Shelf Science, 1994, 39(6): 451-460.
[22] Maggi F, Mietta F, Winterwerp J C. Effect of variable fractal dimension on the floc size distribution of suspended cohesive sediment [J]. Journal of Hydrology, 2007, 343(1-2): 43-55.
[23] Khelifa A, Hill P S. Models for effective density and settling velocity of flocs [J]. Journal of Hydraulic Research, 2006, 44(3), 390-401.
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