LABORATORY MODEL STUDIES OF VERTICAL ROUND BUOYANT JETS IN SHALLOW CROSS-FLOWS

Laboratory experiments have been conducted on the behaviour of vertical round buoyant jets in shallow homogeneous cross-flows. Measured centre-line temperature profiles have been used to determine plume trajectories and minimum dilutions, for a range of experimental conditions. For momentum-dominated (z(M)/z(B) much greater than 1, where z(M) and z(B) are the momentum and buoyancy length scales respectively) shallow hows, trajectory plots show a power law dependence of (z/z(M)) upon (x/z(M)), where z is the vertical coordinate of the dilution minimum at a distance x downstream of the source. Power law indices for various submergence ratios H/D are in agreement with deep water counterparts. Values of the constants of proportionality are found to be significantly less than for deep water momentum-dominated far field (mdff) hows, thus confirming the role of bottom effects in shallow hows. Dimensionless plots of (mdff) centre-line dilutions against x/z for various H/D also showed a power law behaviour over a restricted range of (x/z), with the power law indices found to be in agreement with those from corresponding deep-water cases. Transitions in the dependence of the normalized dilution on (x/z) were obtained at low values of (x/z), this behaviour being ascribed to localized source effects. Shallow depth effects were found to be significant in increasing dilution, through their effect on the constant of proportionality in the power law relationship between the normalized dilution and (x/z). The usefulness of the length scales z(M) and z(B) in parameterizing mixed how cases is discussed.