Hostname: page-component-78c5997874-mlc7c Total loading time: 0 Render date: 2024-11-19T13:34:06.148Z Has data issue: false hasContentIssue false
  • English
  • Français

Experimental investigation of wave boundary layers with a sudden change in roughness

Published online by Cambridge University Press:  26 April 2006

J. Fredsøe ,
B. M. Sumer ,
T. S. Laursen  and
C. Pedersen
J. Fredsøe
Affiliation:
Technical University of Denmark, Institute of Hydrodynamics and Hydraulic Engineering, 2800 Lyngby, Denmark
B. M. Sumer
Affiliation:
Technical University of Denmark, Institute of Hydrodynamics and Hydraulic Engineering, 2800 Lyngby, Denmark
T. S. Laursen
Affiliation:
Technical University of Denmark, Institute of Hydrodynamics and Hydraulic Engineering, 2800 Lyngby, Denmark
C. Pedersen
Affiliation:
Technical University of Denmark, Institute of Hydrodynamics and Hydraulic Engineering, 2800 Lyngby, Denmark
Get access Rights & Permissions [Opens in a new window]

Abstract

This study deals with turbulent oscillatory boundary-layer flows over a plane bed with a sudden spatial change in roughness. Two kinds of ‘change in the roughness’ were investigated: in one, the roughness changed from a smooth-wall roughness to a roughness equal to 4.8 mm, and in the other, it changed from a roughness equal to 0.35 mm to the same roughness as in the previous experiment (4.8 mm). The free-stream flow was a purely oscillating flow with sinusoidal velocity variation. Mean flow and turbulence properties were measured. The Reynolds number was 6 × 106 for the major part of the experiments, with a maximum velocity of approximately 2 m/s and the stroke of the motion about 6 m. The response of the boundary layer to the sudden change in roughness was found to occur over a transitional length of the flow. The bed shear stress over this transitional length attains a peak value over the bed section with the larger roughness. It was found that the amplification in the bed shear stress due to this peak could be up to 2.5 times its asymptotic value. Also, it was found that the turbulence is quantitatively different in the two half periods; a much stronger turbulence is experienced in the half period where the flow is towards the less-rough section. The present experiments further showed that a constant streaming occurs near the bed in the neighbourhood of the junction between the two bed sections. This streaming is directed towards the section with the larger roughness.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 252 , July 1993 , pp. 117 - 145
Copyright
© 1993 Cambridge University Press

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Andreopoulos, J. & Wood, D. H. 1982 The response of a turbulent boundary layer to a short length of surface roughness. J. Fluid Mech. 118, 143–164.Google Scholar
Antonia, R. A. & Luxton, R. E. 1971 The response of a turbulent boundary layer to a step change in surface roughness. Part 1. Smooth to rough. J. Fluid Mech. 48, 721–761.Google Scholar
Antonia, R. A. & Luxton, R. E. 1972 The response of a turbulent boundary layer to a step change in surface roughness. Part 2. Rough to smooth. J. Fluid Mech. 53, 737–757.Google Scholar
Bakker, W. T. 1974 Sand concentration in an oscillatory flow. Proc. 14th Conf. Coastal Engng Copenhagen, pp. 1129–1148.
Bayazit, M. 1976 Free surface flow in a channel of large relative roughness J. Hydraul. Res. 14(I), 115–126.Google Scholar
Belcher, S. E., Xu, D. P. & Hunt, J. C. R. 1990 The response of a turbulent boundary layer to arbitrarily distributed two-dimensional roughness changes. Q. J. R. Met. Soc. 116, 611–635.Google Scholar
Bradley, W. F. 1968 A micrometeorological study of velocity profile and surface drag in the region modified by a change in surface roughness. Q. J. R. Met. Soc. 94, 361–379.Google Scholar
Fredsøe, J. 1984 Turbulent boundary layer in wave-current motion. J. Hydraul. Engng ASCE 110, 1103–1120.Google Scholar
Grant, W. D. & Madsen, O. S. 1979 Combined wave and current interaction with a rough bottom. J. Geophys. Res. 84 (C4)1 1797–1808.Google Scholar
Hagatun, K. & Eidsvik, K. J. 1986 Oscillating turbulent boundary layers with suspended sediment. J. Geophys. Res. 91 (C11)1 13045–13055.Google Scholar
Hino, M., Kashiwayanagi, M., Nakayama, A. & Hara, T. 1983 Experiments on the turbulence statistics and the structure of a reciprocating oscillatory flow. J. Fluid Mech. 131, 363–400.Google Scholar
Jensen, B. L. 1989 Experimental investigation of turbulent oscillatory boundary layers. Thesis, Technical University of Denmark, Institute of Hydrodynamics and Hydraulic Engineering, Lyngby, Denmark.
Jensen, B. L., Sumer, B. M. & Fredsøe, J. 1989 Turbulent oscillatory boundary layers at high Reynolds numbers. J. Fluid Mech. 206, 265–297.Google Scholar
Justesen, P. 1988 Prediction of turbulent oscillatory flow over rough beds. Coastal Engng 12, 257–284.Google Scholar
Justesen, P. & Fredsøe, J. 1985 Distribution of turbulence and suspended sediment in the wave boundary layer. Prog. Rep. 62, 61–67. Inst. of Hydrodyn. & Hydraul. Engng, Technical University, Denmark.Google Scholar
Kajiura, K. 1968 A model for the bottom boundary layer in water waves. Bull. Earthquake Res. Inst. 45, 75–123.Google Scholar
LHermitte, M. P. 1958 Contribution à l’étude de la couche limite des houles progressives. Ministère de la Défense Nationale Secrétariat d’État à la Marine. Comité Central D'Océanographie et D'Étude de Côtes. No. 136.
Longuet-Higgins, M. S. 1957 The mechanics of the boundary-layer near the bottom in a progressive wave. Appendix to R. C. H. Russell & J. C. C. Osorio, An experimental investigation of drift profiles in a closed channel. Proc. 6th Intl Conf. Coastal Engng Miami, Florida, pp. 184–193.
Sleath, J. F. A. 1987 Turbulent oscillatory flow over rough beds. J. Fluid Mech. 182, 369–409.Google Scholar
Spalart, P. R. & Baldwin, B. S. 1987 Direct simulation of a turbulent oscillating boundary layer. NASA Tech. Mem. 89460, Ames Research Center, Moffett Field, CA. (Also in Turbulent Shear Flows 6, Springer.)
Spalart, P. R. & Leonard, A. 1987 Direct numerical simulation of equilibrium turbulent boundary layers. In Turbulent Shear Flows 5 (ed. F. Durst, B. E. Launder, J. L. Lumley, F. W. Schmidt & J. H. Whitelaw), pp. 234–252. Springer.
Sumer, B. M., Laursen, T. S. & FsOSE, J. 1993 Wave boundary layers over a sloping bed. Coastal Engng (submitted).Google Scholar
Townsend, A. A. 1966 The flow in a turbulent boundary layer after a change in surface roughness. J. Fluid Mech. 26, 255–266.Google Scholar
Tsujimoto, T., Urushizaki, M. & Miyagaki, K. 1991 Turbulent flow with abrupt changes of roughness in open channels. KHL Communication, Hydraulics Lab. Dept. Civil Engineering, Kanazawa University, Japan, Progressive Res. Rep./June 1991, pp. 59–78.