Concentration and Velocity Structure of Self-Preserving Steady Round Buoyant Turbulent Plumes in Crossflow

The structure of self-preserving steady round buoyant turbulent plumes in uniform crossflows were studied. The experiments involved a round salt-containing (sodium phosphate) water source jet injected into an ethyl-alcohol/water crossflow to match the refractive indices of the two flows in a water channel. Planar-Laser-Induced Fluorescence (PLIF) was used to measure mean and rms fluctuating concentrations of source fluid whereas Particle-Image-Velocimetry (PIV) was used to measure mean and rms fluctuating velocities, both over cross-sections of the flow. Self-preserving behavior was reached when the plumes were deflected into nearly the crossflow direction, yielding counter-rotating vortex systems similar to self-preserving line thermals. As a result, achieving self-preservation was strongly affected by the source/crossflow velocity ratio, e.g., the self-preserving region was observed for (x$_{c}$-x$_{os})$/d greater than the following values: 25 (u$_{o}$/v$_{\infty }$=5), 110 (u$_{o}$/v$_{\infty }$=50) and 170 (u$_{o}$/v$_{\infty }$=100). At self-preserving conditions, it was possible to construct contour plots of concentration and velocity properties over the flow cross section using scaled self-preserving variables. Another interesting property of these flows is their surprisingly rapid mixing; this was indicated by a flow width for plumes in crossflows that was 2.7 times larger than that of plumes in still surroundings.