Impacts of Non-Divergence-Free Flows On The Coalescence of Initially Distant Buoyant Scalars on a Turbulent Free Surface
Kenneth Pratt
Department of Civil, Environmental, and Architectural Engineering, University of Colorado Boulder
Date and time:
Thursday, November 5, 2015 - 2:00pm
Location:
ECCR 257
Abstract:
Lagrangian Coherent Structures (LCS) have been shown to play a predictive role in the coalescence of initially distant scalars in incompressible flows. Buoyant scalars on the free surface of a 3D incompressible turbulent fluid, however, are advected by a 2D compressible velocity field, resulting in scalar distributions that differ from those seen in a 2D incompressible flow. Our research uses both numerical and experimental approaches to investigate the coalescence of two initially distant reactive scalars to infer the impact of non-divergence-free behavior on buoyant scalar coalescence. Preliminary numerical results, utilizing incompressible and compressible chaotic 2D models, indicate that non-divergence-free behavior increases the likelihood of scalar coalescence and therefore enhances any interactions or reactions between the scalars. In addition, the shape and distribution of LCS is altered in compressible flows, which may explain the increased likelihood of scalar coalescence. Experimentally, we have constructed a 60 X 60 X 60 cm tank that generates three-dimensional turbulence via random pulsing of 36 jets on the tank bottom. Buoyant and initially uniformly distributed florescent particles are tracked on the free surface, and clustering statistics are computed as scalars cluster due to the non-divergence-free property of the free surface. From these results, we hope to elucidate the role of free-surface flow on the coalescence of initially distant buoyant scalars, and extend these results to oceanic mixing problems, such as the transport of phytoplankton blooms and oil spills.