Experimental study of tailwater level and asymmetry ratio effects on three-dimensional offset jets
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Date
2014-08-27
Authors
Durand, Zacharie
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Abstract
Supercritical fluid jets provide a complex flow pattern and are present in many engineering applications. To date, studies have focused on wall jets, free jets, and two-dimensional offset jets. As a result, our understanding of three-dimensional offset jets is lacking. A deeper understanding of three-dimensional offset jets is important as they are seen in many engineering applications. Understanding the flow patterns of three-dimensional offset jets will aid hydraulic engineers to reduce anthropogenic effects when designing new and rehabilitating older hydraulic structures. The purpose of this study was to evaluate the effects of tailwater level and asymmetry ratio on three-dimensional offset jets.
A physical model was constructed and three sets of experiments were conducted. Each set of experiments evaluated the effects of the Reynolds number, tailwater level, or asymmetry ratio. Velocity measurements were taken with an acoustic Doppler velocimeter. The acoustic Doppler velocimeter measured all three components of velocity which allowed the calculation of all six components of Reynolds shear stresses and ten components of triple velocity correlation.
The effects of Reynolds number, tailwater level, and asymmetry ratio on streamwise flow development, distributions of mean velocities, and distribution of turbulence statistics were evaluated. Reynolds number effects were found to be insignificant at Reynolds number greater than 53,000. Two different trends were observed in the behavior of three-dimensional offset jets at different tailwater levels. At low tailwater levels the jet will not reattach to the channel bottom as it does at higher tailwater levels. Increasing the asymmetry ratio of an offset jet will make the jet curve towards the channel wall and bottom faster. Once reattached to the wall the velocity decay rate is greatly reduced.
The results found in this study will be useful to a hydraulic engineer designing new or rehabilitating older hydraulic structures which have flow characteristics similar to that of three-dimensional offset jets. The data acquired during this study adds to the available data usable for calibration and validation of turbulence models. All three components of velocity were measured simultaneously which allowed to calculation of the six Reynolds shear stresses and ten triple velocity correlation terms. All velocities and turbulence statistics in this study were measured simultaneously which provides a data set that has rarely been seen before.
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Keywords
Three-dimensional offset jet, Acoustic Doppler velocimeter, Reynolds number, Tailwater level, Asymmetry Ratio, Offset Jets, Wall Jets, Free Jets