| Summary: | The turbulent motions of buoyant plumes and momentum jets are ubiquitous in both the natural and built environments where a stable density stratification typically persists. The fluid mechanics of turbulent plumes and jets in stratified environments encompasses a fascinating and exigent field of research motivated by an extensive range of practical applications that include low-energy building ventilation, urban air quality management and the dispersion of pollutants in natural water bodies and the atmosphere. Merely as a consequence of vertical variations in the density of the ambient fluid, variations which often occur rapidly with depth in a shallow transitional layer (e.g. oceanic thermoclines and atmospheric inversions) separating two fluid masses, the fundamental behaviour of plumes and jets (in otherwise uniform environments) can be profoundly modified. This thesis investigates theoretically two intrinsic facets of turbulent plumes and jets in stratified environments. First, we examine the classic transport phenomenon of turbulent entrainment across a density interface driven by the localised impingement of a vertically-forced high-Reynolds-number jet. By developing theoretical models, we capture and elucidate the dominant physics at the heart of this complex physical process. Notably, the predictions of these models are in close agreement with existing experimental measurements. By unravelling the effects of confinement imposed by the physical boundaries of a box on the dynamics of interfacial entrainment, we highlight underlying physical reasons for the controversy surrounding the law governing the rate of entrainment across an interface. Second, we examine the time-dependent density stratification that develops in a confined environment following the activation of two turbulent plumes of unequal strengths. We show that the buoyancy of a bounded fluid layer can exceed, or overshoot, its steady value and that the plumes can induce a bulk overturning of the buoyant region. Finally, we discuss the wider context of this research and its application in engineering, the atmospheric sciences and oceanography.
|
|---|
