Using CFD Modeling to Simulate the Control of the Propagation of Salt Wedge using Inclined Roughness Elements

Abstract

This research aims to simulate and use Computational Fluid Dynamics, CFD, to control the propagation of salt wedges. The flume has a cross-section of 25 cm in height and 7.5 cm in width with a length of 6 m and a zero slope. The simulated model is used to investigate the use of inclined roughness elements to control the propagation of salt wedges. The elements are blocks of 2 cm by 3 cm cross-sections having an inclined face in the direction of the flow, with a length of 2 and 3 cm. These elements were installed in two rows at both sides of the bed of the flume with variable spacing between them in the direction of the flow, and their centerline is inclined by an angle of 30 degrees in the direction of the flow. The simulation model was validated by comparing its output with a published laboratory experiment. Ten CFD model runs were conducted under two different discharges and five different spacing between the inclined roughness elements. The used discharges are 30 l/min and 45.3 l/min, and the spacing between elements was 3, 6, 9, 12, and 15 cm. The results demonstrated a good relationship between the obtained model runs and the observations of the laboratory experience under the same conditions. The result showed that when no roughness elements were used, the propagation of the salt wedge extended to 3.9 and 3.1 m at a discharge of 30 l/min and 45.31 l/min, respectively. The propagation of the salt wedge is reduced as the spacing increases to some limit and then starts to decrease when you use roughness elements. At the maximum applied discharge of 45.3 l/min, the propagation of the salt wedge was reduced by 82, 84, and 85% when the spacing between the blocks is 3, 6, and 9 cm, respectively. The percentage of reduction in the propagation of the salt wedge starts to reduce to 79% and 75% as the spacing between the blocks is increased to 12 and 15 cm, respectively. When the discharge is 30 l/min, the propagation of the salt wedge is reduced by 76, 74, and 78% at a spacing of 3, 6, and 9 cm, respectively. At the same time, the propagation is reduced by 58% at 12 cm and 53% as the spacing is increased to 12 and 15 cm.