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

Subject Areas : Subjects

N. Berahmand ¹ (استادیار گروه مهندسی عمران ‌دانشگاه ‌آزاد ‌اسلامی واحد لارستان، لارستان، ایران)
S.R. Mosavi ² (دانشچوی کارشناسی ارشد سازه های هیدرولیکی، گروه مهندسی عمران دانشگاه ‌آزاد ‌اسلامی، واحد یاسوج ، یاسوج، ایران)

Received: 2013-09-16 Accepted : 2013-09-16 Published : 2013-03-21

Keywords: density current, bed slope discontinuity, Numerical Simulation, vertical velocity profile, vertical concentration profile,

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.

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