Numerical simulation of density currents near bed with slope reduction using various turbulent models

Document Type : Research Paper

Authors

Abstract

Gravity or density current is produced due to a density contrast among two different fluids or among two layers of a single fluid. In this research work, the saline gravity current near bed  with slope reduction was simulated numerically, using FLUENT software. The experimental results were used in order to calibrate the numerical model. The obtained results showed that density current was simulated accurately, using turbulent model (RNG type) and optimized grid. This result was found especially for the vertical profiles of local velocity and volumetric concentration (for both sub and supercritical sections), the density height, the maximum value of mean velocity and the corresponding height of this velocity. The numerical results showed that both standard and RNG turbulent model was accurate for calculation of saline gravity current height.  In this paper, using turbulent model (RNG type), better similarity collapses of velocity profiles were obtained in comparison with concentration profiles. Moreover, due to ambient water height limitation, a circulation flow was found in numerical results. Finally, the numerical model indicated that for given initial conditions, as initial bed slope increases, the location of the density jump is moved farther downstream, and also the amount of ambient water entrained along the supercritical regions increases with the increase of the initial bed slope.

Keywords


  1. 1 .صفایی اردکـانی، ا.، ح. افشـین، و ب. فیروزآبـادی. 1386 .

    بررسی تجربی ساختار جریان چگال سه بعـدی. ششـمین

    کنفـرانس هیـدرولیک ایـران. دانشـگاه شـهرکرد. 13-15

    شهریور.

    2 .فیروزآبـــادی، ب.، س.م.ر. موســـوی حکمتـــی و س.ع.

    حسینی. 1384 .بررسی تجربی رسوبگذاری دو بعدی و سه

    بعـدی مغشـوش. پنجمـین کنفـرانس هیـدرولیک ایـران.

    دانشگاه شهید باهنر کرمان. 7-19 آبان ماه.

    1. Alavian, V. 1986. Behavior of density

    currents on an incline. J. Hydraul. Eng.

    112: 27–42.

    1. Altinakar, M.S., W.H. Graf, and E.J.

    Hopfinger. 1996. Flow structure in

    turbidity currents. J. Hydraul. Res. 34:

    713–718.

    1. Aram, E., and B. Firoozabadi. 2007.

    Numerical simulation and experimental

    investigation of 3-dimensional confined

    density currents. Int. J. Dynamics of

    Fluids. 3: 45-62.

    1. Choi, S.U., and M.H. Garcia. 2002.

    k - e turbulence modeling of density

    currents developing two dimensionally on

    a slope. J. Hydraul. Eng. 128: 55-63.

    1. Eidsvik, K.J. and B. Brørs. 1989. Selfaccelerated turbidity current prediction

    based upon ( k - e ) turbulence. Cont. Shelf

    Res. 9: 617–627.

    1. Farrel, G.J., and H. Stefan. 1988.

    Mathematical modeling of plunging

    reservoir flows. J. Hydraul. Res. 26: 525–

    537.

    1. Firoozabadi, B., B. Farhanieh, and M. Rad.
    2. The Propagation of turbulent density

    currents on sloping bed. J. Scientia of

    Iranica. 8: 223–235.

    1. Firoozabadi, B., B. Farhanieh, and M. Rad.
    2. Hydrodynamics of two-dimensional,

    laminar turbid density currents. J. Hydraul.

    Res. 41: 623-630.

    1. Forel, F.A. 1892. The´orie du ravin souslacustre. Le le´man, Vol. 1, F. Rouge,

    Lausanne, Switzerland, 381–386.

    1. Garcia, M.H. 1993. Hydraulic jumps in

    sediment-driven bottom currents. J.

    Hydraul. Eng. 119: 1094-1117.

    1. Hartel, C., E. Meiburg, and F. Necker.
    2. Analysis and direct numerical

    simulation of the flow at a gravity-current

    head. Part 1. Flow topology and front

    speed for slip and no-slip boundaries, J.

    Fluid Mech. 418: 189–212

    1. Huang, H., J. Imran, and C. Primez. 2005.

    Numerical model of turbidity currents with

    a deforming bottom boundary. J. Hydraul.

    Eng. 131: 283-293.

    1. Imran, J., A. Kassem, and S.M. Khan.
    2. Three-dimensional modeling of

    density current. I. Flow in straight confined

    and unconfined channels. J. Hydraul. Res.

    42: 578–590.

    1. Kostic, S. and G. Parker. 2006. The

    response of turbidity currents to a canyonfan transition: internal hydraulic jumps and

    depositional signatures. J. Hydraul. Res.

    44: 631-653.

    1. Lambert, A., and F. Giovanoli. 1988.

    Records of riverborne turbidity currents

    and indications of slope failures in the

    Rhone Delta of Lake Geneva. Limnology

    and Oceanography. 33(3).

    1. Launder, B., and B. Sharma. 1974.

    Application of the energy-dissipation

    model of turbulence to the calculation of

    flow near a spinning disc. Letters in Heat

    Mass Transfer. 1: 131–138.

    1. Lee, H.Y., and W.S. Yu. 1997.

    Experimental study of reservoir turbidity

    current. J. Hydraul. Eng. 123: 520–528.

    1. Mehdizadeh, A., and B. Firoozabadi. 2009.

    Simulation of a density current turbulent

    flow employing different RANS models: A

    comparison study. Scientia Iranica,

    Transaction B: Mechanical Engineering

    16: 53-63.

    1. Parker, G., Y. Fukushima, and H.M.

    Pantin. 1986. Self-accelerating turbidity

    currents. J. Fluid Mech. 171: 145–181.

    1. Simpson, J.E. 1987. Gravity currents in the

    environment and the laboratory. Ellis

    Harwood, Chi Chester, U.K.

    1. Skene, K.I., T. Mulder, and J.P.M.

    Syvitski. 1997. INFLO1: A model

    predicting the behaviour of turbidity

    currents generated at river mouths.

    Comput. Geosci. 23: 975– 991.

    1. Stacey, M.W., and A.J. Bowen. 1988a. The

    vertical structure of density and turbidity

    currents: theory and observations. J.

    Geophys. Res. 93(C3): 3528–3542.

    1. Stacey, M.W., and A.J. Bowen. 1988b.

    The vertical structure of turbidity currents

    and a necessary condition for selfmaintenance. J. Geophys. Res. 93(C3):

    3543–3553.

    1. Toniolo, H., and G. Parker. 2003. 1D

    numerical modeling of reservoir

    sedimentation. Proc., IAHR Symposium on

    River, Coastal and Estuarine

    Morphodynamics. Barcelona, Spain. 457-

    468.

    1. User’s guide manual of FLUENT software,

    version 5.0. 1998. Incorporated, Lebanon,

    N.H.