EXPERIMENTAL AND NUMERICAL STUDY ON VELOCITY FIELDS AND WATER SURFACE PROFILE IN A STRONGLY-CURVED 90° OPEN CHANNEL BEND

The flow pattern changes at open channel bend as the result of the presence of centrifugal force. Parameters such as water surface level, the transverse and depth velocity distribution, secondary flow and separation zones deeply depend on bend angel and radius, while many researchers are interested in flow patterns at bends. This paper presents an experimental and numerical study of the flow patterns in a strongly-curved 90 degrees open channel bend. The numerical modelling was carried out using the finite volume method. In this numerical study, the k - epsilon (RNG) model was used to predict the turbulence, and the volume of fluid (VOF) method was used to simulate the water free surface. The numerical results were verified against data from a program of experiments conducted in this study. A comparison between the experimental data and the results of the numerical model showed that the k - epsilon (RNG) and VOF methods are capable of simulating the flow pattern in the strongly-curved bends. The results showed that along a strongly-curved 90 degrees bend, the maximum flow velocity always occurs near the inner wall and in such bends the effect of the secondary flows is not limited to the sections within the bend. Also the overall shape of streamlines along the bend and at different water levels is different. In addition, the results revealed that the transverse slope of the water surface is non-linear in these bends. This situation occurs in bends even though maintaining a steady uniform flow condition in straight sections.