Joseph D. Olles

Optical performance of an oscillating, pinned-contact double droplet liquid lens

Liquid droplets can produce spherical interfaces that are smooth down to the molecular scale due to surface tension. For typical gas/liquid systems, spherical droplets occur on the millimeter and smaller scales. By coupling two droplets, with contact lines pinned at each edge of a cylindrical hole through a plate, a biconvex lens is created. Using a sinusoidal external pressure, this double droplet system (DDS) can be readily forced to oscillate at resonance. The resulting change in the curvatures of the droplets produces a time-varying focal length. Such an oscillating DDS was introduced in 2008 [Nat. Photonics 2, 610 (2008)]. Here we provide a more comprehensive description of the systems optical performance, showing the effects of liquid volume and driving pressure amplitude on the back focal distance, radii of curvature, object distance, and image sharpness.

kHz Rate Digital In-line Holography Applied to Quantify Secondary Droplets from the Aerodynamic Breakup of a Liquid Column in a Shock-Tube

The breakup of liquids due to aerodynamic forces has been widely studied. However, the literature contains limited quantified data on secondary droplet sizes, particularly as a function of time. Here, a column of liquid water is subjected to a step change in relative gas velocity using a shock tube. A unique digital in-line holography (DIH) configuration is proposed which quantifies the secondary droplets sizes, three-dimensional position, and three-component velocities at 100 kHz. Results quantify the detailed evolution of the characteristic mean diameters and droplet size-velocity correlations as a function of distance downstream from the initial location of the water column. Accuracy of the measurements is confirmed through mass balance. These data give unprecedented detail on the breakup process which will be useful for improved model development and validation.

Phase behavior of oscillating double droplets

Double droplet systems are comprised of two coupled spherical interfaces. These systems are effective harmonic oscillators, due to their low dissipation and fast response; features enabled by their pinned contact lines. Here, millimeter scale coupled droplets of water are actuated with a sinusoidal driving pressure. The phase and transient behavior of the driven double droplet system is characterized. With the exact position of the double droplets determined, implementation of devices such as tunable lenses, thermal switches, and liquid adhesion mechanisms can be realized.

Characterizing the propensity of hypervelocity metal fragments to initiate plastic bonded explosives

The off-normal detonation behavior of two plastic-bonded explosive (PBX) formulations was studied using explosively-driven aluminum fragments created by two types of detonators. A generic aluminum-cupped detonator contained 100 mg of PETN which was sufficient to fragment the aluminum into hundreds of sub-mm particles moving at hypersonic velocity; for comparison, a Teledyne RISI® RP-80 was also tested which generated a more substantial flyer plate of aluminum. Low-density polystyrene foam was used as a witness material with subsequent computed tomography analysis to characterize the distribution of particles post-test. Precise digital in-line holography experiments were conducted in situ to measure three-dimensional shape and size of the fastest-moving fragments as they impacted PBXs. Fragments showed significant variability in size, shape and distribution or clustering. Depending on the shot, single or multiple shock impacts could be imparted to the PBX from the generic detonator fragments, or clusters, ...

Characterizing the growth to detonation in HNS with small-scale PDV “cutback” experiments

For many decades, cutback experiments have been used to characterize the equation of state and growth to steady detonation in explosive formulations. More recently, embedded gauges have been used to capture the growth to steady detonation in gas-gun impacted samples. Data resulting from these experiments are extremely valuable for parameterizing equation of state and reaction models used in hydrocode simulations. Due to the extremely fast growth to detonation in typical detonator explosives, cutback and embedded gauge experiments are particularly difficult, if not impossible. Using frequency shifted photonic Doppler velocimetry (PDV) we have measured particle velocity histories from vapor-deposited explosive films impacted with electrically driven flyers. By varying the sample thickness and impact conditions we were able to capture the growth from inert shock to full detonation pressure within distances as short as 100 µm. These data are being used to assess and improve burn-model parameterization and equ...