Humberto Bocanegra Evans

Measuring droplet size distributions from overlapping interferometric particle images

Interferometric particle imaging provides a simple way to measure the probability density function (PDF) of droplet sizes from out-focus images. The optical setup is straightforward, but the interpretation of the data is a problem when particle images overlap. We propose a new way to analyze the images. The emphasis is not on a precise identification of droplets, but on obtaining a good estimate of the PDF of droplet sizes in the case of overlapping particle images. The algorithm is tested using synthetic and experimental data. We next use these methods to measure the PDF of droplet sizes produced by spinning disk aerosol generators. The mean primary droplet diameter agrees with predictions from the literature, but we find a broad distribution of satellite droplet sizes.

Flow Around an Autonomous Underwater Vehicle With Bio-Inspired Coating

Flow separation is a major factor in the form drag experienced by a moving object. In particular, suppressing or reducing flow separation is critical in the reduction of energy expenditure of autonomous underwater vehicles. Previous research suggests that bio-inspired micro-fibrillar structures are capable of reducing the boundary layer separation in a turbulent flow. Here, we present laboratory measurements using particle tracking velocimetry near the wall of two submersible vessel models: one coated with an array of micro-fibers and a second one with smooth walls. The flow around the vessels was enticed by the ordered micro-fibers to retain higher velocities near the wall of the vessel. The experiments suggest that separation of the flow may be reduced by the use of the bio-inspired micro-fibers. Keywords—Bio-inspired, Drag reduction, Flow Separation,