Elias Panides

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.

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