ENERGY-LOSS AT COMBINING PIPE JUNCTION

Energy loss data for a 90-degrees 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 upstre am 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 bra nch to main-pipe discharge Q(b)/Q(d) ranging from 0 to 1. At flow situ ations defined by these ranges there are few energy loss data availabl e and no satisfactory theory. The study includes an investigation of s pecific flow features at the junction including the velocity and press ure 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 assoc iated with: (1) The deflection and distortion of the branch-flow veloc ity distribution prior to the exit of the branch flow into the main pi pe; 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 pi pe diameters downstream from the pipe junction.