Journal of Food, Agriculture and Environment

Roughness effects on hydraulic jumps in density currents

Author(s):

Nader Barahmand ^1*, Abolfazl Shamsai ¹, Mehdi Ghomshi ²

Recieved Date: 2011-01-12, Accepted Date: 2011-03-30

Abstract:

Hydraulic jumps in density currents significantly influence the environmental characteristics of lakes and dam reservoirs. In this study, the density jump is investigated experimentally by considering the bed roughness. For both smooth and rough beds, the laboratory experiments were carried out using a 0.4 m wide, 0.9 m deep, and 8.3 m long flume. The flume bed had a slope discontinuity that was similar to the one in the canyon-fan system. Using the gravel particles that were glued closely on the horizontal part of the bed, four rough beds were examined. The results showed that the amount of ambient water entrained along the jump and supercritical regions increases with the increase of the initial bed slope; but the effect of bed roughness on the amount of freshwater entrained along these regions was negligible. It was found that if the upstream densimetric Froude number is specified, the sequent depth ratio increases as the relative roughness decreases. An empirical relationship was also determined for calculating the sequent depth ratio as a function of the upstream densimetric Froude number and the relative roughness. Finally, the behavior of saline gravity currents in the vicinity of a slope discontinuity was simulated numerically using both the layer-averaged Navier-Stokes equations and the proposed relationship. The effects of initial bed slope and roughness on the density jump were studied. The numerical model indicated that for given initial conditions, as initial bed slope increases, the location of the density jump is moved farther downstream; also, this position is pushed farther downstream with the decrease of the bed roughness.

Keywords:

Density jump, sequent depth ratio, relative roughness, densimetric Froude number, numerical model

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Journal: Journal of Food, Agriculture and Environment
Year: 2011
Volume: 9
Issue: 2
Category: Environment
Pages: 531-534

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