Flow Separation Downstream of Equal and Opposing Flow Junctions in Open Channels

It is common in different open channel flow systems, such as cooling tower basins, irrigation systems, and other water distribution systems, for two flows of equal magnitude to collide and then turn 90-degrees into a downstream channel. When this occurs two separation zones are formed in the downstream channel. This separation is often of interest during the design or evaluation of these types of structures to evaluate the potential for a hydraulic jump or choked flow conditions to occur. Numerous studies of open channel junctions have been conducted but very little information exists for the particular case of two opposing flows which collide and turn 90-degrees. This paper presents the results of a physical model study to evaluate the separation zones in this hydraulic phenomenon. The physical model study was used to validate an analytical method of the opposing flow condition. There was good agreement between analytical method and the physical model. The validated analytical method approach can be used to predict the maximum width of the separation zone. This paper summarizes the results of these studies and presents an analytical tool which can be used to asses the potential for hydraulic jumps or choked flow conditions in cooling towers, irrigation channels, and a variety of other water distribution applications.