Advected turbulent line thermal driven by concentration difference

Abstract

The spatial evolution of an advected line thermal driven by concentration difference - a turbulent buoyant body of fluid, for which small density difference is caused by a proportional variation in scalar concentration, horizontally introduced at no excess momentum into a horizontal ambient current, is studied using the standard two-equation k-ε model with a buoyancy expansion. The numerical results show that the advected line thermal is characterized longitudinally by a flat trajectory with scalar dilution taking place essentially near the jet exit, and transversely by a vortex-pair flow and a kidney-shaped concentration structure with double peak maxima corresponding to stronger buoyancy effect; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless distance of around 10; the aspect ratio for the kidney-shaped sectional thermal is found to be around 1.2-1.4; the predicted flow feature and mixing rate are well supported by asymptotic dimensional analysis and related experimental data. The analogy between a steady advected line thermal and corresponding time-dependent line thermal is also found reasonable by a special exploration into the horizontal velocity distribution and the significance of horizontal diffusion effect of the advected line thermal. Only about half of the vertical momentum resulting from the buoyancy effect is found contained in the advected line thermal, corresponding to an added virtual mass coefficient of approximately 1 for the sectional thermal. © 2002 Elsevier Science B.V. All rights reserved.