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Tailwater effects on the characteristics of a square jet near a free-surface

Author(s): Girish Sankar; Ram Balachandar; Rupp Carriveau

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Keywords: Confined square jet; free surface; jet flow; tailwater effect; turbulence characteristics

Abstract: Characteristics of a square jet near a free surface were experimentally studied at four different tailwater depths. Velocity measurements were made with a two-component laser Doppler anemometer at five stations along the jet streamwise axis. A qualitative assessment was made of the location of jet impingement on the free surface. The results reveal that the tailwater depth has little influence on the mean velocity distribution beyond a certain depth. Turbulence intensities and shear stress profiles indicate jet anisotropy and higher spread rates than an axi-symmetric free jet. The analysis of third-order moments divulged a marked increase in the turbulent ejection and entrainment events for the jet as the tailwater depth increased and the effect of free surface confinement was reduced. A quadrant analysis confirmed that the confinement effect due to the proximity of the free surface acted to curtail the ability of the jet to eject or entrain fluid.


Year: 2008

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