Investigation of equal and opposing flow junctions

Abstract

This paper presents an experimental study of a 90° channel junction with equal and opposing flow in the upstream main channel. The aim of the study is to predict the size of the recirculation zones in the downstream branch channel that are formed as the flow makes a 90° turn after colliding and the associated energy loss. Detailed three-dimensional velocity profiles are measured with an acoustic Doppler velocimeter in the upstream main channel and downstream branch channel for different width ratios of the main and branch channels and inlet Froude numbers. The velocity profiles are depth-averaged to determine the maximum width of the recirculation zones in the branch channel. The velocity and flow depth distributions in the main and branch channels near and within junctions are dependent on inlet Froude number and channel width ratio. An analytical model based on mass, momentum and energy principles is developed and used to predict the maximum width of the recirculation zones. The maximum relative error in the predicted maximum width of the separation zone is less than 6·5%.