VERTICAL ROUND AND ORTHOGONAL BUOYANT JETS IN A LINEAR DENSITY-STRATIFIED FLUID KYRIAKI KONSTANTINIDOU 1 121 Analypseos St, 38 333 Volos, Greece PANOS N. PAPANICOLAOU 2 Asst. Professor, Department of Civil Engineering, University of Thessaly Pedion Areos, 38 334 Volos, Greece Tel: 2421-74113, FAX: 2421-74169, e-mail: panospap@uth.gr ABSTRACT Turbulent round and orthogonal jets with rounded corners and aspect ratio 2:1, issuing into a linear density-stratified calm ambient fluid, have been investigated experimentally. The terminal height of rise and the mean elevation of the horizontal spreading have been measured in a series of experiments that extend from pure momentum jets to plumes. The data confirm the asymptotic analysis made for the two limiting flows, a jet and a plume. A round jet rose higher from an orthogonal one with the same initial kinematic characteristics. This result is congruent with earlier measurements showing that elliptical jets with a 2:1 axis ratio entrained almost twice as much (uniform) ambient fluid as the corresponding round ones. Experiments showed that the dimensionless terminal height of rise in round plumes is lower from that observed in orthogonal ones, meaning that they entrain more ambient fluid if they disperse vertically into a linear density stratification. The dimensionless rise height parameters are found to be different in jets and plumes for both types of nozzles round and orthogonal. A numerical study of the terminal height of rise of round buoyant jets showed that the entrainment coefficient measured earlier in a plume if applied to the flow can reproduce it quite accurately, while in the jet regime it has to be reduced drastically, in order to reproduce the experimental data. Keywords. Buoyant jet, round, orthogonal, linear density gradient, calm ambient, rise height, horizontal spreading, experiments, numerical solution. 1. INTRODUCTION The mechanics of a rising buoyant jet in a density stratified, calm ambient fluid, is of great theoretical and practical interest, especially when it is applied in the design of treated wastewater ocean outfalls, and in the smoke stack design. Both, the atmosphere and the oceans are density stratified. A buoyant jet discharge mixes with the surrounding ambient fluid as it propagates vertically up to an elevation where it becomes neutrally buoyant. The non-zero yet vertical kinematic momentum flux, will force it to a greater elevation, where its kinematic buoyancy flux becomes negative. At a certain elevation the vertical momentum flux vanishes (all the kinetic energy has been converted into potential energy). In the literature, this has been defined as "the terminal height of rise" (THR) of a buoyant jet in a density stratified fluid. Subsequently, since it becomes heavier from the surrounding fluid, it sinks and spreads horizontally around some mean elevation of neutral density. The terminal rise height of the jet 1 Present Address: Grad. Student, Department of Civil Engineering, Aristotle University of Thessaloniki 2 To whom correspondence should be addressed.