2023, Razie Akbari Graduated

Numerical and experimental modeling of forced hydraulic jump by a vertical sill

Abstract

Scouring is a surface process that removes the river bed or beaches materials due to the interaction of water and soil. Scouring is one of the major causes of failure for stream and river projects. The three-dimensional flow around bridge piers along with the transfer of sediment and the constant change of the flow boundaries causes the complexity of the flow patterns. It difficult to analyze this phenomenon by numerical and analytical methods. Therefore, most researches are based on experimental researches. So far, many methods have been used to modify the flow patterns and control scouring at the bridge piers.

The present research used an active control method initiated by the electromagnetic Lorentz force in the scouring process. The experimental model is a homemade system built in the hydraulic laboratory of the faculty of civil engineering at Isfahan University of Technology. Experiments were performed in a channel with a rectangular cross-section of 0.31 m width, 0.30 m height, and 5.7 m length. A cylindrical pier made of polyethylene with a diameter of 25 mm and a height of 300 mm was used. To install the electromagnetic parts on the cylindrical pier, a strip arrangement of the copper electrode and magnet parts with a width of 5 mm and a length of 150 mm were used. Sediments with an average diameter of 0.2 and 0.3 mm and a relative density of 2.77 were used. Scouring tests were performed in the clear water in the presence of an electromagnetic field in both upward and downward directions of the Lorentz force, in sodium hydroxide fluid with a conductivity of 3 siemens per meter and applying a constant voltage of 30 volts for a period of one hour. Moreover, additional tests in drinking water fluid with the same condition as in scouring tests in sodium hydroxide fluid have been performed.

The tangential Lorentz force on the cylindrical pier caused an acceleration of 0.45 m/s² to the sodium hydroxide fluid. When the Lorentz force is parallel to the direction of the downward flow, the increasing acceleration caused an increase in the velocity of the flow and, consequently, a 10% increase in the dimensions of the scour hole (length, width, and depth). In this case, the sediment transport in downstream has decreased 15% due to the downward deviation of the flow angle separated on the pier sides. By adjusting the direction of the Lorentz force opposite to the direction of the downward flow, the decreasing acceleration caused a decrease in the velocity of the downward flow, a 10% increase of the length, width, and upstream depth of the scour, and an increase of 30% of the downstream scour depth. The results show that increasing the depth of the fluid flow increases the efficiency of the Lorentz force in order to control the scour. When the direction of the Lorentz force is opposite to the direction of the downward flow, the depth of scour hole in sodium hydroxide solution is 6% greater than the depth of scour hole in drinking water without the electromagnetic field.