Turbulent Underflow in a Short Channel of Limited Depth

The flow characteristics of a turbulent underflow in a horizontal channel of limited depth are explored analytically and experimentally under a variety of upstream and downstream control conditions. Freshwater and salt water are used in the physical model to simulate a stable density stratification, and a contraction is adopted as a downstream control device. Three typical flow situations, respectively, distinguished as drowned internal jump, free internal jump, and flow instability, are observed depending on the nature of the interaction between the upstream and downstream controls. The hydraulic properties of each one of the flow situations are reviewed, and the experimental observations are compared with the results obtained from a hydraulic analysis. Maximum turbulent mixing is demonstrated to occur at a particular value of the discharge densimetric Froude number. Further increase of discharge densimetric Froude number is expected to result in a decrease in turbulent mixing and eventually to provoke a flow instability.