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

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.