Peter Hamlington, Department of Mechanical Engineering, University of Colorado Boulder
The Structure and Dynamics of Puffing Plumes
The near-field characteristics of highly buoyant plumes, commonly referred to as lazy plumes, remain relatively poorly understood across a range of flow conditions, particularly compared to our understanding of far-field characteristics. Buoyant plumes are found in a wide range of naturally occurring phenomena (e.g., volcanic eruptions, hydrothermal vents, and fire plumes) and engineering applications (e.g., heat treatment processes, desalination plants, and space heaters). The distinguishing feature of these flows is the presence of a dominant buoyant force resulting from density variations in the presence of a gravitational field. In each of these flows, when lower density fluid is injected into higher density ambient fluid, the plume contracts laterally, producing large coherent vortical structures that rise vertically, opposite to the direction of gravity. This process repeats continuously, resulting in a characteristic “puffing” behavior. The frequency at which vortices are shed is the most studied characteristic of this instability, and much research has been devoted to developing scaling relations for the frequency based on plume inlet parameters. In this talk, we use three-dimensional numerical simulations of buoyant plumes across a range of conditions and configurations to characterize the effects of inlet shape, inlet Richardson and Reynolds numbers, and two-plume interactions on the puffing frequency. We focus, in particular, on the development of scaling relations for the puffing frequency, the identification of the laminar to turbulent flow transition, and the role of Rayleigh-Taylor instabilities in the plume structure and dynamics.