Abstract: Background turbulence disrupts the jet structure resulting in its rapid decay (mean velocity and passive scalar concentration) and a reduced entrainment, before jet breakdown when only turbulent diffusion acts. The effect of the background turbulence is characterized by its relative length scale, L, and turbulence intensity, ξ, with ξ dominating the jet dynamics in the self-similar region. Large scales of the ambient turbulence advect the jet. Jet breakdown occurs at ξ = 0.5, while for ξ < 0.5, entrained small scales cause faster decay of the jet’s large vortical structures and transfer of their energy to smaller scales. They also increase the jet rms increasing the radial scalar transport and differential diffusion, thereby increasing the mixing. Entrainment occurs across the turbulent/turbulent interface, the TTI, identified by a larger sharp jump in mean and rms passive scalar concentration, which is longer, more tortuous and has a higher fractal dimension than its quiescent counterpart, the TNTI.

Curriculum Vitae: Susan Gaskin is a Brace Professor in Civil Engineering at McGill University. Her main focus of research is experimental environmental fluid mechanics with a focus on the fundamental processes of turbulent entrainment and mixing particularly of jets in turbulent ambient flows, turbulent ambient flows being ubiquitous in the environment and common in industrial flows.  She is also interested in the hydraulics of hydropower, river engineering particularly fluvial erosion of cohesive sediments and, in water resources management, basin wide hydrologic modelling, sustainable water supply and the health impacts of trace metals therein.