Turbulence Structures in Flow over Two-Dimensional Dunes

This paper presents a large eddy simulation (LES) of turbulent open channel flow over two-dimensional periodic dunes. The Reynolds number R based on the bulk velocity U (bulk) and the maximum flow depth h , is approximately 25,000. The instantaneous flow field is investigated with special emphasis on the occurrence of coherent structures. Instantaneous vortices were visualized and it is shown that separated vortices are formed downstream of the dune crest due to Kelvin–Helmholtz instabilities. Near the point of reattachment the so-called kolk-boil vortex evolves in form of a hairpin vortex. Also present are previously separated vortices, which are convected along the stoss side of the downstream dune and elevated toward the water surface. The existence of near wall streaks which reform shortly after reattachment is also shown. The spacing between two low-speed streaks is very similar to that observed previously over smooth and rough walls. For validation, profiles of the time-averaged velocities, streamwi...

[1]  Coherent Structures In Open-Channel Flows Over a Fixed Dune , 2005 .

[2]  Iehisa Nezu,et al.  Turbulence in open-channel flows , 1993 .

[3]  D. B. Simons,et al.  Forms of bed roughness in alluvial channels , 1961 .

[4]  P. Moin,et al.  A dynamic localization model for large-eddy simulation of turbulent flows , 1995, Journal of Fluid Mechanics.

[5]  P. Moin,et al.  A dynamic subgrid‐scale eddy viscosity model , 1990 .

[6]  I. Nezu,et al.  Three-dimensional structure of space-time correlation on coherent vortices generated behind dune crest , 1999 .

[7]  Jinhee Jeong,et al.  On the identification of a vortex , 1995, Journal of Fluid Mechanics.

[8]  P. Engel.  Length of Flow Separation over Dunes , 1981 .

[9]  李幼升,et al.  Ph , 1989 .

[10]  H. Shen,et al.  Investigation of Turbulent Flow over Dunes , 1990 .

[11]  C. R. Smith,et al.  The characteristics of low-speed streaks in the near-wall region of a turbulent boundary layer , 1983, Journal of Fluid Mechanics.

[12]  S. Mclean,et al.  Turbulent flow over three-dimensional dunes: 1. Free surface and flow response , 2003 .

[13]  R. Street,et al.  Turbulent flow over a wavy surface: Neutral case , 2001 .

[14]  Ugo Piomelli,et al.  Large-Eddy Simulations: Theory and Applications , 1996 .

[15]  V. C. Patel,et al.  Assessment of PIV to measure mean velocity and turbulence in open-channel flow , 2003 .

[16]  J. Best,et al.  Turbulence and coherent flow structures associated with bedform amalgamation: An experimental study of the ripple-dune transition , 2000 .

[17]  V. C. Patel,et al.  Numerical model of turbulent fl ow over a sand dune , 1996 .

[18]  S. Mclean,et al.  Turbulence structure over two‐dimensional bed forms: Implications for sediment transport , 1994 .

[19]  Jochen Fröhlich,et al.  Highly resolved large-eddy simulation of separated flow in a channel with streamwise periodic constrictions , 2005, Journal of Fluid Mechanics.

[20]  J. Smagorinsky,et al.  GENERAL CIRCULATION EXPERIMENTS WITH THE PRIMITIVE EQUATIONS , 1963 .

[21]  J. Smith,et al.  Mechanics of flow over ripples and dunes , 1989 .

[22]  D. B. Simons,et al.  Summary of alluvial channel data from flume experiments, 1956-61 , 1966 .

[23]  J. B. Perot,et al.  Shear-free turbulent boundary layers , 1994 .

[24]  V. C. Patel,et al.  Large-Eddy Simulation of Turbulent Flow over a Fixed Two-Dimensional Dune , 2006 .

[25]  J. Best.  The fluid dynamics of river dunes: A review and some future research directions , 2005 .

[26]  V. C. Patel,et al.  Large eddy simulation of turbulent open-channel flow with free surface simulated by level set method , 2005 .

[27]  D. Lyn.  Turbulence Measurements in Open‐Channel Flows over Artificial Bed Forms , 1993 .

[28]  Vincenzo Armenio,et al.  A Lagrangian Mixed Subgrid-Scale Model in Generalized Coordinates , 2000 .

[29]  V. De Angelis,et al.  Direct numerical simulation of turbulent flow over a wavy wall , 1997 .

[30]  G. K. Gilbert,et al.  The Transportation of Débris by Running Water , 2010 .

[31]  Christof Hinterberger,et al.  Dreidimensionale und tiefengemittelte Large-Eddy-Simulation von Flachwasserströmungen , 2004 .

[32]  D. Lilly,et al.  A proposed modification of the Germano subgrid‐scale closure method , 1992 .

[33]  Parviz Moin,et al.  Shear-free turbulent boundary layers. Part 1. Physical insights into near-wall turbulence , 1995, Journal of Fluid Mechanics.

[34]  R. Soulsby,et al.  A comparison of numerical model experiments of free surface flow over topography with flume and field observations , 1993 .

[35]  Bruce W. Melville,et al.  Initiation of Bed Forms on a Flat Sand Bed , 1996 .

[36]  B. Rhoads,et al.  Structure of flow over alluvial bedforms: an experiment on linking field and laboratory methods , 2006 .

[37]  M. V. Mierlo,et al.  Turbulence measurements above artificial dunes , 1988 .

[38]  A. Soldati,et al.  Mechanisms for deposition and resuspension of heavy particles in turbulent flow over wavy interfaces , 2006 .

[39]  Three-dimensional coarse large-eddy simulations of the flow above two-dimensional sinusoidal waves , 2001 .

[40]  A. Müller,et al.  On the vortex formation in the mixing layer behind dunes , 1986 .