Investigating the characteristics of the density current due to changes in the flow regime

The density current is a relative movement that occurs between two fluid layers, even if they slightly vary in density. The difference in specific mass may be due to temperature, suspended matter, dissolved materials, or a combination of them. These flows are especially important in cases such as the inflow of muddy rivers into the reservoirs of dams or seas and lakes, and can have different effects, such as sedimentation in dams and river estuaries to the sea, the change of the coastal beds and continental shelf areas. Therefore, the study of this type of motion and the effect of changing the regime from the supercritical to the subcritical (the creation of a hydraulic jump) is very influential regarding flow characteristics. The study of fluid flow requires the identification of velocity profiles in the flow path. For this purpose, by applying a physical model and creating a flow with different input characteristics and imposing regime change conditions, the velocity profiles in the flow body were measured and the flow characteristics were analyzed. The results showed that the coefficients of the velocity profiles in the wall and jet areas were 0.82, 0.87 and 2.83 respectively for subcritical flows and 1.174, 1.26 and 2.9 for supercritical currents. Other results include a 14 to 19 percent reduction in speed and a 21 to 32 percent increase in flow depth due to the jump. In addition, in some cases, there were significant difference between the results of the analytical jump relationship and the experimental data

Effect of freshwater river level, seawater density, and efficiency of air bubble curtain system on preventing saline water intrusion in surface water

Water quality is crucial to the development and management of water resources. Therefore, maintaining water quality, especially freshwater, which constitutes the major human consumption for a variety of drinking, agricultural, and industrial uses is important. Water quality is reduced by various natural and anthropogenic factors. One of the most common and important processes that reduces the quality of water resources is the influence of saline sea water on surface water. Seawater infiltration is a natural process due to the difference in the density of seawater from fresh water. Seawater is denser than fresh water because of the presence of minerals such as salt. The higher density of seawater causes it to be submerged under freshwater and, on the contact surface, seawater penetrates into the freshwater wedge. Salt water intrusion of sea toward the river caused a decrease in the quality of fresh water which makes it useless for utilizing in agricultural, industrial, and drinking and led to obliterating this fertilized plain upon its infiltration into the surrounding land. In order to reduce these negative effects through hydraulical control of salt water intrusion, we need to know about the efficacious mechanism of this issue. Thus, this study using ANSYS Fluent for modeling salt water intrusion on the surface water examined influences of changing in the sea water density and the water level of river on the measure of salinity intrusion. Also, air bubble curtain system as an alternative to preventing salt water intrusion was investigated. Results showed that sea water density and the water level of river had direct relationship with salinity intrusion, which means that upon an increase in the sea water density or the water level of river, salt water intrusion will increase, vice versa. Therefore, penetrating salinity increased by 86% with an 0.2% increase in saltwater density and was decreased %45 by decreasing %19 at river water level. Air bubble curtain system by creating impeding bubble between salt and fresh water is an appropriate solution for preventing salt water intrusion