Gerald A. Domoto

Laser induced short plane acoustic wave focusing in water

Laser induced high frequency acoustic wave generation, propagation, and focusing in water are studied. A large area, flat, and short duration acoustic wave was generated by the thermoelastic interaction of a homogenized short pulsed laser beam with the liquid-solid interface and propagated at the speed of sound. Laser flash Schlieren photography was used to visualize the transient interaction of the flat acoustic wave with a cylindrical concave lens and the subsequent acoustic wave focusing. Numerical simulations showed the acoustic wave could be focused to several tens of microns in size and 7bars in pressure.

Compressible flow of liquid in a standing wave tube

Particle image velocimetry (PIV) has been applied to the study of acoustic flow of liquid in a standing wave tube. Even though liquid compressibility is very small, the liquid must be treated as compressible in this case. With the finite compressibility of liquid in mind, a series of different standing wave modes can be formed by pressure waves emanated at specific driving frequencies from a bimorph piezo disk at the end of the tube. In this paper, the first three natural standing wave modes were visualized using 1 μm diameter fluorescent microspheres seeded in the liquid. The variation of the flow field in the acoustic boundary layer near the wall was measured using PIV. Water was first used as a working fluid. Experiments were then carried out with a glycerol-water mixture (50%-50% by volume) to examine the effect of viscosity change on the wave propagation and flow structure inside the tube. The experimental results are compared with theoretical model predictions.

Laser induced plane acoustic wave generation, propagation, and interaction with rigid structures in water

Short pulsed laser induced single acoustic wave generation, propagation, interaction with rigid structures, and focusing in water are experimentally and numerically studied. A large area short duration single plane acoustic wave was generated by the thermoelastic interaction of a homogenized nanosecond pulsed laser beam with a liquid-solid interface and propagated at the speed of sound in water. Laser flash schlieren photography was used to visualize the transient interaction of the plane acoustic wave with various submerged rigid structures [(a) a single block, (b) double blocks, (c) 33° tilted single block, and (d) concave cylindrical acoustic lens configurations]. Excellent agreement between the experimental results and numerical simulation is observed. Our simulation results demonstrate that the laser induced planar acoustic wave can be focused down to several tens of micron size and several bars in pressure.

Free-surface Taylor vortices

The hydrodynamic instability of a viscous incompressible flow with a free surface is studied both numerically and experimentally. While the free-surface flow is basically two-dimensional at low Reynolds numbers, a three-dimensional secondary flow pattern similar to the Taylor vorticies between two concentric cylinders appears at higher rotational speeds. The secondary flow has periodic velocity components in the axial direction and is characterized by a distinct spatially periodic variation in surface height similar to a standing wave. A numerical method, using boundary-fitted coordinates and multigrid methods to solve the Navier-Stolces equations in primitive variables, is developed to treat two-dimensional free-surface flows

Dynamics of a wire in positive corona discharge

This theoretical and experimental investigation studies the corona induced oscillation of a wire located near a ground plane. The corona is created by a high, positive dc, potential difference between the wire and the plane. The motion of 1.5 and 3.5 mil inch diameter wires is optically measured. The effects of voltage, mechanical tension, spacing, and several other primary operating parameters are explored experimentally. Neutral stability curves are determined. A theoretical model of the wire motion is presented. The model considers the high voltage driver circuitry, the conduction of current through air and the wire dynamics. The wire motion is obtained numerically. The model is linearized and a stability analysis is performed. The constraints on the operating parameters that are necessary for stable equilibrium are discussed. The results are compared to measured data.

Pulsed laser induced acoustic wave propagation and interaction in liquid: experiment and simulation

In-situ experimental work on laser induced pressure waves in water is presented in this paper. A double frequency Nd:YAG laser(532 nm, 4 ns pulse width) was irradiated on a chromium thin film on quartz substrate in contact with water. A plane pressure wave with high temporal and spatial resolution was generated by the laser induced thermoelastic stress around 8~12 mJ/cm2 below the regime of shock wave generation. The pressure wave was observed to propagate at the speed of sound in water. The plane acoustic wave could be interacted and focused with solid structures. FEM numerical simulations of the aforementioned phenomena are also carried out to solve the 2D transient wave equation and compared with the experimental results.

Numerical Method of Unsteady Viscous Microchannel Fluid Flows

This paper presents a numerical method for predicting 2-D and 3-D slightly compressible flow along microchannels, in which, one dimension is much smaller than the others (such as in ink jet printerheads). Both the configuration and the slightly compressible character of the fluid are very typical in practice and are amenable to simplification of the Navier-Stokes equations for more efficient calculation. Based on assumptions of these particular configurations and the fluid property, simplified systems of Navier-Stokes equations are obtained. Bicharacteristic based numerical calculations are developed to solve the systems of simplified, slightly compressible, viscous, Navier-Stokes equations. Two dimensional results are compared with analytical solutions. Three-dimensional results are compared with the results of commercial CFD code. Satisfactory agreements have been obtained and great efficiency has been achieved.Copyright

Numerical Computation of Fluid Flow and Heat Transfer in Microchannels

A finite difference numerical approach for solving slightly compressible, time-dependent, viscous laminar flow is presented in this study. Simplified system of Navier-Stokes equations and energy equation are employed in the study in order to perform more efficient numerical calculations. Fluid flow and heat transfer phenomena in two dimensional microchannels are illustrated numerically in this paper. This numerical approach provides a complete numerical simulation of the development of the fluid flow and the temperature profiles through multi-dimensional microchannels.Copyright

Numerical simulation of charge transport in ionographic printing

The utilization of air entrainment for transport and control of charge deposition in ionographic printing is investigated numerically. The geometries considered can be thought of as a charge generation region followed by an air entrainment region followed by an ion projection region. The air entrainment region provides a zone in the ion flow path where moderate electrode voltages can be applied to achieve stable and accurate control and modulation of the ion current levels. Results of the numerical simulations showing effects of air flow and modulation voltage on ion trajectories are presented.