3D NUMERICAL AND EXPERIMENTAL INVESTIGATION OF SUPERCRITICAL FLOWS AT CHANNEL BENDS

Abstract

The centrifugal force generated by open channel flow around curves will push the water particles away from main stream to radial direction. In order to maintain water particle equilibrium at the bend section, a differential rise in water surface beside the outside wall and a depression along the inside wall is created. This water surface rise causes a pressure force ΔP to balance the flow against the centrifugal force. The rise of water surface above the mean water level is called Superelevation. Due to steep terrain natures, land acquisition, innovative flood mitigation designs in urban areas, inaccurate cited equations for estimation of superelevation at bends. Accordingly it is essential to investigate 3D flow field around bends, establish design charts for superelevation at supercritical flow (Fr = 1.3 – 2) with sharp bends where r/b<3, to determine the bend outer walls height, and study the extended bend protection against high shear stresses for these sharp bends. These objectives are achieved through creating a 3D numerical model for rectangular channels with different bends degrees using Ansys Fluent Launcher, and carrying an experimental runs using a rectangular flume on laboratory for measuring the water surface profile for bend with angles of 90o to calibrate the results of the numerical model as no field data are available. The results of this study address design charts for calculating the superelevation at sharp open channel bends, address a modified equation for the protection length downstream the bend (Lp) after adding the effect of r/b ratio, confirm the three flow regions around open channel bends after matching them with the predefined regions in the previous studies, and identify the locations of maximum superelevation along the bend radial section.