Experimental Investigation of Three-Dimensional Nonbuoyant Rectangular Jets

The behavior of a nonbuoyant three-dimensional rectangular water jet with aspect ratios of 5, 10, and 20 were investigated based on experimental results of the mean velocity field obtained by particle image velocimetry. The theoretical centerline velocity equation derived from the point source concept using the spreading rate for the axisymmetric jet gave velocity results that agreed well with the measured centerline velocity, and provided the potential core region, two-dimensional region, and axisymmetric region. The similarities of the measured cross-sectional velocity profiles along both major and minor axes were verified. In the two-dimensional region, the Gaussian constant and Strouhal number tended to be preserved, and the spreading rate decreased at the end of the two-dimensional region. In the transition zone between the two-dimensional and the axisymmetric regions, the centerline velocity decay rate and the spreading rate were observed to drop, whereas the Gaussian constant and Strouhal number were found to increase with axial distance. The range of the two-dimensional region demarcated by the criterion of the theoretical centerline velocity decay was very similar to those based on the conservations of the Gaussian constant and Strouhal number, and that based on the change in the spreading rate along the minor axis.