Mean flow and turbulence structure over fixed, two‐dimensional dunes: implications for sediment transport and bedform stability

Sedimentology - Tập 42 Số 3 - Trang 491-513 - 1995
Sean J. Bennett1, Jim Best1
1Department of Earth Sciences, University of Leeds, Leeds LS2 9JT, West Yorkshire, UK

Tóm tắt

ABSTRACTDetailed measurements of flow velocity and its turbulent fluctuation were obtained over fixed, two‐dimensional dunes in a laboratory channel. Laser Doppler anemometry was used to measure the downstream and vertical components of velocity at more than 1800 points over one dune wavelength. The density of the sampling grid allowed construction of a unique set of contour maps for all mean flow and turbulence parameters, which are assessed using higher moment measures and quadrant analysis. These flow field maps illustrate that: (1) the time‐averaged downstream and vertical velocities agree well with previous studies of quasi‐equilibrium flow over fixed and mobile bedforms and show a remarkable symmetry from crest to crest; (2) the maximum root‐mean‐square (RMS) of the downstream velocity values occur at and just downstream of flow reattachment and within the flow separation cell; (3) the maximum vertical RMS values occur within and above the zone of flow separation along the shear layer and this zone advects and diffuses downstream, extending almost to the next crest; (4) positive downstream skewness values occur within the separation cell, whereas positive vertical skewness values are restricted to the shear layer; (5) the highest Reynolds stresses are located within the zone of flow separation and along the shear layer; (6) high‐magnitude, high‐frequency quadrant‐2 events (‘ejections’) are concentrated along the shear layer (Kelvin‐Helmholtz instabilities) and dominate the contribution to the local Reynolds stress; and (7) high‐magnitude, high‐frequency quadrant‐4 events occur bounding the separation zone, near reattachment and close to the dune crest, and are significant contributors to the local Reynolds stress at each location. These data demonstrate that the turbulence structure associated with dunes is controlled intrinsically by the formation, magnitude and downstream extent of the flow separation zone and resultant shear layer. Furthermore, the origin of dune‐related macroturbulence lies in the dynamics of the shear layer rather than classical turbulent boundary layer bursting. The fluid dynamic distinction between dunes and ripples is reasoned to be linked to the velocity differential across the shear layer and hence the magnitude of the Kelvin‐Helmholtz instabilities, which are both greater for dunes than ripples. These instabilities control the local flow and turbulence structure and dictate the modes of sediment entrainment and their transport rates.

Từ khóa


Tài liệu tham khảo

10.1017/S0022112087000272

10.1115/1.3243545

Allen J.R.L., 1982, Sedimentary Structures: their Character and Physical Basis, 539

10.1016/0037-0738(84)90052-6

Bagnold R.A.(1966)An approach to the sediment transport problem from general physics.U.S. geol. Surv. Prof. Pap.422–I.

10.1017/S0022112088001545

10.1017/S0022112088001557

Bennett S.J.andBest J.L.(1995)Structure of turbulence over two‐dimenional dunes. In:Sediment Transport Mechanisms in Coastal Environments and Rivers(Ed. byM. M.BerlorgeyandJ. F. A.Sleath) in press.

Best J.L.(1995)The fluid dynamics of small‐scale alluvial bedforms. In:Advances in Fluvial Dynamics and Stratigraphy(Ed. byP.A.CarlingandM.Dawson) in press.

10.1017/S0022112086002094

Bradshaw P., 1971, An Introduction to Turbulence and its Measurement, 218

10.1017/S002211207200299X

10.1029/91WR02570

10.1111/j.1365-3091.1988.tb01249.x

10.1146/annurev.fl.11.010179.002303

Clifford N.J., 1993, Turbulence: Perspectives on Flow and Sediment Transport, 93

10.1144/GSL.SP.1993.075.01.04

10.1016/0037-0738(69)90010-4

Costello W.R.(1974)Development of bed configurations in coarse sands.PhD thesis Massachusetts Institute of Technology Cambridge .

DANTEC(1991)Particle Dynamics Analyzer: User's Manual.107pp. Dantec Elektronik.

10.1029/WR025i005p00911

10.1029/92WR01357

Durst F., 1987, Principles and Practice of Laser‐Doppler Anemometry, 405

Engel P., 1981, Length of flow separation over dunes, ASCE J. Hydraul. Div, 107, 1133, 10.1061/JYCEAJ.0005738

10.1146/annurev.fl.14.010182.000305

10.1017/S0022112078001275

10.1080/00221687909499590

Fehlman H.M.(1985)Resistance components and velocity distributions of open channel flows over bed forms.MS thesis Colorado State University Ft Collins .

10.1111/j.1365-3091.1993.tb01763.x

10.1115/1.2910168

Grass A.J., 1974, Transport, Erosion and Deposition of Sediment in Turbulent Streams, Proc. Euromech 48, 33

Guy H.P., 1966, Summary of alluvial channel data from flume experiments, 1956–1961, U.S. geol. Surv. Prof. Pap, 462, 96

Hayashi T., 1970, Formation of dunes and antidunes in open channels, ASCE J. Hydraul. Div, 96, 357, 10.1061/JYCEAJ.0002324

Hubbell D.W., 1987, Laboratory data on coarse‐sediment transport for bedload sampler calibrations, U.S. geol. Surv., Water Supply Pap, 2299, 31

Itakura T., 1980, Proc. 3rd International Symposium on Stochastic Hydraulics, 599

10.1017/S0022112076002243

10.1080/00221689009499075

10.1080/00221689309498846

10.1017/S0022112063000975

10.1146/annurev.fl.01.010169.001051

Korchokha Y.M., 1968, Investigation of the dune movement of sediments on the Polomet's River, Sov. Hydrol, 11, 541

10.1016/0037-0738(93)90073-E

Landahl M.T., 1986, Turbulence and Random Processes in Fluid Mechanics, 154

10.1029/TR025i006p00900

10.1002/esp.3290170305

10.1017/S0022112088000916

10.1144/gsjgs.137.4.0423

10.1111/j.1365-3091.1983.tb00687.x

10.1061/(ASCE)0733-9399(1983)109:3(718)

10.1061/(ASCE)0733-9429(1991)117:4(399)

10.1017/S0022112073000315

10.1017/S0022112087000235

10.1061/(ASCE)0733-9429(1993)119:3(306)

10.1007/978-1-4615-7408-8

10.1029/TR028i002p00255

McCorquodale J.A., 1973, Flow over natural and artifical ripples, Proc. 15th Congr. Int. Ass. Hydraul. Res, 1, A22

10.1016/0012-8252(0)90032-Q

10.1061/(ASCE)0733-9429(1986)112:4(300)

10.1029/94JC00571

10.1061/(ASCE)0733-9429(1990)116:4(459)

10.1061/(ASCE)0733-9429(1992)118:9(1222)

10.1017/S0022112087002866

Müller A., 1982, Mechanics of Sediment Transport, 41

10.1080/00221688609499314

10.1017/S0022112094000170

10.1080/00221688709499289

10.1029/WM012p0069

Nelson J.M., 1989, Mechanics of flow over ripples and dunes, J. Geophys. Res, 94, 8146, 10.1029/JC094iC06p08146

10.1029/93WR01932

Nezu I., 1993, Turbulence in Open‐channel Flows, 281

Nezu I. Nakagawa H. Tominaga A.andYoshikawa M.(1980)Visual study of large‐scale vortical motions in open‐channel flows. In:Ann. Conf. Jap. Soc. civ. Engrs. Kansai‐Branch II–10(in Japanese).

Nordin C.F., 1975, Flume studies with fine and coarse sand, a preliminary analysis, Int. Symp. River Mech, 501

10.1017/S0022112071001605

Raudkivi A.J., 1963, Study of sediment ripple formation, ASCE J. Hydraul. Div, 89, 15, 10.1061/JYCEAJ.0000952

10.1017/S0022112066001356

10.1017/S002211208000078X

Rifai M.F., 1969, Pressure fluctuations in reattaching flow: discussion, ASCE J. Hydraul. Div, 95, 1747, 10.1061/JYCEAJ.0002178

Rifai M.F., 1971, Flow over triangular elements simulating dunes, ASCE J. Hydraul. Div, 97, 963, 10.1061/JYCEAJ.0003041

10.1146/annurev.fl.23.010191.003125

10.1139/e89-183

10.1061/(ASCE)0733-9429(1990)116:6(799)

10.1017/S0022112093002691

10.1146/annurev.fl.21.010189.001225

Simons D.B., 1961, Flume studies using medium sand (0–45 mm, U.S. geol. Surv. Water Supply Pap, 1498, 76

10.1029/JC075i030p05928

10.1029/JC082i012p01735

Soulsby R.L., 1991, Sand Transport in Rivers, Estuaries and the Sea, 155

10.1017/S0022112081001092

10.1017/S0022112078001020

10.1029/JZ072i024p06183

10.1111/j.1365-3091.1989.tb00820.x

Tritton D.J., 1988, Physical Fluid Dynamics, 519

Knapp F.C.M., 1991, Sand Transport in Rivers, Estuaries and the Sea, 179

VanMierlo M.C.L.M.anddeRuiter J.C.C.(1988)Turbulence measurements above artificial dunes.Rept. TOW A55 Q789 pp.1–42. Delft Hydraulics.

Vanoni V.A., 1967, Relation between bed forms and friction in streams, ASCE J. Hydraul. Div, 93, 121, 10.1061/JYCEAJ.0001607

Vanoni V.A., 1960, Resistance properties of sediment‐laden streams, Trans. Am. Soc. civ. Eng, 125, 1140, 10.1061/TACEAT.0007902

10.1080/00221687709499747

10.1017/S0022112091001416

10.1029/92JC01228

10.1029/JC094iC04p05011

Williams G.P., 1967, Flume experiments on the transport of a coarse sand, U.S. geol. Surv. Prof. Pap, 562, 31

10.1007/BF02085931

10.1111/j.1365-3091.1989.tb01533.x

Willmarth W.W., 1974, Turbulent Diffusion in Environmental Pollution, 287

Yalin M.S., 1977, Mechanics of Sediment Transport, 298

Yalin M.S., 1992, River Mechanics, 219

10.1080/00221688309499450

Thông tin
Thông tin xuất bản

Sedimentology

Tập 42 Số 3

491-513

Thông tin tác giả