Droplet formation under the effect of a flexible nozzle plate.

Droplet formation from a flexible nozzle plate driven by a prescribed-waveform excitation of a piezoelectric is numerically investigated using a computational fluid dynamics (CFD) model with the volume of fluid (VOF) method. The droplet generator with a flexible nozzle plate, which is free to vibrate due to the pressure acting on the plate, is modeled in a CFD computational domain. The CFD analysis includes the fluid-structure interaction between fluid and a flexible plate using large deflection theory. The problem is characterized by the nondimensional variables based on the capillary parameters of time, velocity, and pressure. The CFD model is validated with the experiment results. This study examines the characteristics of the applied waveforms and nozzle plate material properties to change the vibrational characteristics of the nozzle plate. The effect of fluid properties on the droplet formation process is also investigated focusing on surface tension and viscous forces. Increasing the impulse of the piezoelectric can be used to cause a higher droplet velocity and it is shown that the vibration of the nozzle plate has a strong effect on the droplet velocity, shape, and volume. Surface tension has a strong influence on the droplet formation characteristics in contrast to viscous forces. For the combination of a fluid with high surface tension and the most flexible nozzle plate, this system cannot cause the droplet ejected out of the nozzle.

Three-dimensional image reconstruction using interferometric data from a limited field of view with noise.

A reconstruction of phase objects using an algebraic reconstruction technique in an unconfined environment from multidirectional interferometric data is presented. The effect of noise on the data from the interference patterns is studied. It is shown that in the presence of noise the number of iterations need to be critically evaluated; otherwise the solution tends to diverge. Criteria used to quantify the noise are presented. Also shown is a relationship between noise and the required number of iterations, which yields the least error in reconstruction. This procedure is applied to experimentally obtained interferometric data.

Holocinematographic velocimetry: resolution limitation for flow measurement.

The goal of developing a holocinematographic velocimeter (HCV) is to provide a technique to study the evolution of instantaneous 3-D velocity profiles in turbulent flow fields. The method tracks individual seed particles that have been introduced into the flow. An imaging system using far-field holography is used to provide a full field of view tracking. Velocity information is determined from measured particle displacements of sequential hologram reconstruction. This study examines the resolution limits of far-field holographyas applied to the HCV. The results aid in the determination of required seeding concentrations, establish the ability to resolve particle centers, and illustrate the use of a dual TV camera system to aid resolution. A straightforward enhancement technique provides a means to eliminate noise and reduce out of image plane ambiguity.