Project 3. Oil Jet in Crossflow - Droplet Size Distribution

In the first part of the project, large-eddy simulations were conducted using the Mixture multiphase model for the release of diesel oil from a one-inch (2.5 cm) vertical pipe in a crossflow at 0.27 m/s. The ratio of jet velocity to crossflow speed was 5.0 and the Reynolds number based on jet velocity and pipe diameter was 7100. The impact of the oil buoyancy was captured by adding a transport term to the volume fraction equation. The interactions between the jet and crossflow yielded small-sized flow structures near the upper boundary of the plume. The wake vortices initiated from the leeward side of the plume showed an alternating vorticity pattern in the wake. The shear layer vortices were induced by Kevin-Helmholtz instabilities mostly on the windward side of the plume. The formation of counter-rotating vortex pair (CVP) altered greatly the hydrodynamics of the jet from that of a vertical jet to manifest flow reversals in all directions. The formation of CVP is likely to enhance the mixing of chemicals and droplets within the plume.

Published paper for details: Daskiran, C., Cui, F., Boufadel, M.C., Zhao, L., Socolofsky, S.A., Ozgokmen, T., Robinson, B. and King, T., 2020. Hydrodynamics and dilution of an oil jet in crossflow: The role of small-scale motions from laboratory experiment and large eddy simulations. International Journal of Heat and Fluid Flow, 85, p.108634.

In the second part, two Lagrangian particle tracking techniques were explored, one with the inertia of the droplet is considered and the other that treats the droplets as massless particles with rising velocities corresponding to their size. We did not note a large difference between the two approaches. The droplets showed stronger segregation in the vertical direction, which renders the usage of a Gaussian distribution approximation in the vertical inapplicable. The droplets 500 microns and larger escape the vortex while smaller ones get trapped within the vortex. A similar outcome was observed using a vortex trapping function based on inward-outward force balancing at the elevation of the vortex core. The CVP altered the distribution of droplets of 1 mm and smaller significantly, and bimodal concentration distributions with peaks near the CVP vortex cores and minimum concentration near the center plane were obtained in the lateral-horizontal direction. Therefore, measurements of the oil droplet size distribution (DSD) in the center plane of crossflow jets could underestimate the number of small droplets in the whole plume.

Published paper for details: Daskiran, C., Cui, F., Boufadel, M.C., Socolofsky, S.A., Katz, J., Zhao, L., Ozgokmen, T., Robinson, B. and King, T., 2021. Transport of oil droplets from a jet in crossflow: Dispersion coefficients and Vortex trapping. Ocean Modelling, 158, p.101736.