Estimation of overall droplet size distribution from a local droplet size distribution for a jet in crossflow: Experiment and multiphase large eddy simulations

A local droplet size distribution (DSD) from a jet in crossflow can overestimate or underestimate the overall DSD in the plume based on the measurement location. The overall DSD is crucial to evaluate the fate of oil droplets in the water column for a proper countermeasure following an oil spill. We present experimental results of a vertical oil jet in crossflow with a jet velocity of 2.4 m/s and a crossflow speed of 0.31 m/s, resulting jet-to-crossflow velocity ratio of 7.7 and a jet Reynolds number of 13,400. We measured the droplet size near the top and bottom boundaries of the plume while filming the whole plume. We conducted multiphase large eddy simulations coupled with a population balance model considering the relative velocity among the phases in the momentum and volume fraction equations. The computed plume boundaries and the DSD from the simulations agreed well with the measurements. The Sauter mean diameter and DSD considering all droplets across the plume cross-sections were found to be changing slightly beyond s/D≈15. By considering different plume cross-sections for s/D> 15 and different droplet breakage rates, the overall DSD in a plume cross-section can be obtained locally near thevertical centerline of the plume cross-section (y/D = 0) at (58.8 ± 6.2)% of the plume cross-section height from the bottom boundary of the plume. The trajectory of the local DSD representing the overall DSD was found slightly below the plume trajectory.