Combining Flows in 90° Junctions of Rectangular Closed Conduits

The charactertistics of combining flows past 90° junctions of rectangular closed conduit are studied to determine the various parameters such as power and energy loss coefficients, average entry angle of the branch flow, and the momentum transfer from the branch to the main conduit. Detailed pressure and velocity distribution data were obtained to understand the flow processes involved. Both the mean and fluctuating components of the velocity field were determined in the flow sections immediately downstream of the junction. The contraction coefficient of the flow and the geometry of the separation bubble were determined for a few representative cases. The results of the study indicated that the flow process in junctions of rectangular conduits and circular pipes are very different especially when the discharge ratio is large and the size of the branch conduit is very small compared to the main conduit. However, in some ranges of the discharge ratios and area ratios, the gross flow characteristics such as the dependence of energy loss coefficients on discharge ratios have similar trends. Simple empirical models are developed to determine the transfer of momentum ΔM and the contraction coefficient Cc for 90° junction of rectangular conduit flows. The predicted values ΔM and Cc for three area ratios and several discharge ratios are verified with the help of experimental data.