Energy Loss at Combining Pipe Junction

Energy loss data for a 90° sharp‐edged combining pipe junction were obtained, using a 37‐m long, 444‐mm diameter plastic pipe with a branch pipe entering about 35 pipe diameter downstream from the upstream end of the pipe. The data cover ratios of branch to main‐pipe cross‐sectional areas $A_b/A_d$ ranging from 0.02 to 0.21 and ratios of branch to main‐pipe discharge $Q_b/Q_d$ ranging from 0 to 1. At flow situations defined by these ranges there are few energy loss data available and no satisfactory theory. The study includes an investigation of specific flow features at the junction including the velocity and pressure distribution in the branch flow at its exit into the main pipe. A momentum analysis is performed to show that a satisfactory description of the momentum balance must include the momentum contributions associated with: (1) The deflection and distortion of the branch‐flow velocity distribution prior to the exit of the branch flow into the main pipe; and (2) the increase in wall shear stress in the main pipe due to the local deformation of the main‐flow velocity distribution. The data show that the fully developed pipe flow is re‐established about 50 pipe diameters downstream from the pipe junction.