Aerodynamic Instability and Atomization Processes of Liquid Sheets
C. F. Lee,* B. H. Liou* (Computat. Sci. & Engr.)
University of Illinois

Atomization of liquid sheets is of primary importance for many industrial applications. Models for prediction of instability and disintegration of liquid sheet jets are being developed. Aerodynamic instability that occurs at a disturbed two-phase interface is studied by using perturbation analysis. Detailed numerical simulation of the unstable waves on the two-phase interface is conducted to extend the analytical model well into the nonlinear breakup regime. The resulting models for sheet jets will be incorporated into a multidimensional code for computations of internal combustion engines.

Analysis of Flow and Transport in Subway Systems
W. E. Dunn,* B. R. Green
U.S. Army, DOE ANL 980072401

The flow in subway systems is influenced by many factors. Included among these are (a) the action of the trains, (b) the operation of the heating ventilating and cooling systems, (c) natural convection flows created by thermal gradients and height differentials within the system, (d) external wind, and (e) turbulence. This project is an experimental and numerical study of these flows with an eye toward better understanding and thus being able to more accurately predict transport within the system.

Atmospheric Boundary Layer Modeling
W. E. Dunn,* D. F. Brown
U.S. Army, DOE ANL 981402401

The atmospheric boundary layer is a convectively driven unstable turbulent boundary layer during the day and a stable turbulent boundary layer at night. The boundary layer is constantly changing owing to the diurnal cycle of solar heating of the ground. Our atmospheric boundary layer model treats (a) short wavelength solar heating, (b) long wavelength radiation exchange between the ground and the atmospheric, (c) sensible and latent convective heat transfer through a multilayer plant canopy, and (d) conduction to the ground. We are collecting high quality data at several sites around the country to validate and improve this model.

Buoyant Convection during Semiconductor Crystal Growth with a Magnetic Field
J. S. Walker*
National Aeronautics and Space Administration, NAG8-1453

During the crystal growth of an alloy of two semiconductors, one compound is rejected into the melt, producing variations in the composition of the melt. Since one compound has a much larger density than the other, the compositional variations drive a buoyant convection which may lead to unacceptable nonuniformities in the crystal. A strong magnetic field damps this convection, leading to much better crystals. Models are being developed to predict crystal properties as functions of magnetic field strength and of other parameters. Predictions will be compared to experimental results obtained at the NASA Marshall Space Flight Center.

Drop Dynamics and Speciation in Isolation of Metals from Liquid Wastes
A. J. Pearlstein,* A. Scheeline (Chemistry), M.-P. Shiue
U.S. Department of Energy, DE-FG07-97ER14837

High-temperature thermal treatment is a potentially promising approach to isolation of radioactive and otherwise hazardous metals from liquids. We are conducting computational and experimental investigations of the dynamics of liquid drops in high-temperature gas flows, with particular emphasis on how heat and mass transfer affect metal speciation. The computational work focuses on understanding how flow internal and external to drops affects transport and speciation, with particular emphasis on the drop's wake. This involves extending our previous work to higher density ratios, different viscosity ratios, accounting for thermal effects (e.g., variable surface tension), and ultimately, multicomponent mass transfer.

Effects of Rotation on Bridgman Solidification of Binary Alloys
A. J. Pearlstein,* H. Lee
National Science Foundation, CTS 9422770

'Freckling' and other compositional nonuniformities in directionally solidified alloys are of concern in producing single-crystal turbine blades and other high-strength components and electro-optic materials (e.g., mercury cadmium telluride). These defects have been related to a morphological instability and buoyancy-driven convection in the melt adjacent to the growing interface. To date, we have shown that rotation (acting through the Coriolis acceleration) can suppress convection in a horizontally unbounded layer, and (through the Coriolis and centrifugal accelerations) can affect the melt-solid interface curvature in a cylindrical ampoule.

Experimental Investigation of Refrigerant/Oil Flows Using an Ambient Pressure Flow Visualization Facility
T. A. Newell,* T. Shedd, X. Bai
22 Company Consortium: Air Conditioning and Refrigeration Center, National Science Foundation, EEC 96-12120

A flow visualization loop using refrigerant R123 is being constructed. A novel optical measurement system is being developed for nonintrusive measurement of two-phase flow parameters.

Falling Film Behavior-Maps to Include Vapor Shear, Dry-Out, and Flooding
A. M. Jacobi,* Y. Wei
NSF I/UCRC Air Conditioning and Refrigeration Center; American Society of Heating, Refrigerating and Air-Conditioning Engineers

When a liquid film falls from one horizontal tube to another below it, the flow may take the form of discrete droplets, jets, or a continuous sheet. This flow mode plays an important role in the wetting, heat transfer, and mass transfer characteristics of the falling-film heat exchanger, but there have been no reliable methods for predicting the mode behavior. This research is directed toward generalizing our earlier work on this topic in order to understand how a flow in the surrounding vapor affects the liquid falling-film mode.

Flow Diagnostics and Acoustic Behavior of a Fan-and-Coil Assembly
J. C. Dutton,* R. L. Weaver* (Theo. & Appl. Mech.), S. Balachandar* (Theo. & Appl. Mech.), A. M. Jacobi,* K. D. Smith, S. E. Zeller
NSF I/UCRC Air Conditioning and Refrigeration Center

This project is directed at obtaining a detailed understanding of the velocity, pressure, and acoustic fields surrounding a fan-and-coil unit that is typical of those found in AC/R systems. Mean, fluctuating, and spectral measurements of these quantities will be obtained in both the near- and far-fields. Using the flow and acoustical data, the role that the fan-coil unit plays in generating system noise will be determined. Furthermore, the flow features responsible for this noise will be identified, and methods will be recommended for managing the flow to avoid the generation of objectionable noise.

Fluctuation in Fully Developed Pipe Flow of a Dense Suspension and Transport Parameters
C. F. Lee,* Y. Xu
University of Illinois

Fully developed pipe flow of a dense suspension is characterized by low-frequency fluctuations in wavy stratified flow in a horizontal pipe. Upgrading synchronized measurements of laser Doppler velocimetry and phase Doppler particle analyzer gives components of fluctuating velocities and densities of particle suspensions where particle-particle interactions are significant when compared to particle-wall interactions. Data permits closure of the time-averaged equations for the predictions of stress components in a flowing suspension. Advances include optics and software for determining the local instantaneous density, velocity components, and diffusivities of particle clouds from their passage through the laser-measuring volume.

Fluid Mechanics of Electrodeposition to High Aspect Ratio Through-Holes in Printed Circuit Boards
A. J. Pearlstein,* D. L. Cotrell
National Science Foundation, CTS 94-22770

Rapid and uniform deposition of copper on the inner surface of high aspect ratio 'through-holes' of printed circuit boards is important in electronics manufacture. We are investigating a new approach using a rotating screw electrode (RSE) inside the hole. In addition to improving the electric field distribution, the RSE generates a 3-D flow that greatly enhances mass transfer. Experiments show that plating uniformity is excellent. In the theoretical work, we consider the Navier-Stokes equations for the time-dependent flow between the RSE and the through-hole wall. We have developed a numerical code to compute this flow, and are currently validating it.

Helical Flow-amplified Electrophoretic Separation of Enantiomers Differentially Complexed to Chiral Carriers
A. J. Pearlstein,* H. Gao, C. Tellez, K. D. Cole (NIST), V. L. Vilker (NIST)
National Science Foundation, CTS 9613241; NIST Coop. Agreement 70NANB740059

Many drugs, pesticides, and other biologically active compounds are chiral, existing in left- and right-handed mirror images called enantiomers. In most cases, the desired activity resides in one enantiomer. Thus, separation of enantiomers is of interest. Enantioselective complexation with a chiral carrier (e.g., vancomycin) gives rise to an effective electrophoretic mobility difference, which we will amplify using an axisymmetric annular swirl flow. Computational work will guide fabrication of an electrophoresis cell at NIST, and will focus on effects of diffusion, electric field strength, geometry, and swirl. Buoyant or electrohydrodynamic secondary flows will also be assessed.

Indium-Phosphide Crystal Growth by the Liquid-encapsulated Kyropoulos Process with a Magnetic Field
J. S. Walker*
National Aeronautics and Space Administration, NAG8-1453

Many optoelectronic devices require indium-phosphide (InP) crystals with small defect densities. Most crystal-growth processes involve large temperature gradients, and the associated thermal stresses produce large defect densities in the weak InP crystals. The liquid-encapsulated Kyropoulos process involves crystal growth with very small temperature gradients, so that the InP crystals have very small defect densities. A magnetic field is needed to stabilize the melt motion and to eliminate turbulent temperature fluctuations. Analytical and numerical models are being developed to guide process optimization. The purpose of the modeling effort is to complement an experimental program being conducted at an air force laboratory.

Instantaneous Measurements of Molecular Mixing in High Reynolds Number Shear Flows
J. C. Dutton,* R. P. Lucht,* T. R. Meyer
National Science Foundation, CTS 94-23280

The objectives of this research are the development and application of a technique for quantitative measurements of the structure of high Reynolds number gaseous shear flows (forced and unforced jets and shear layers). The extent of mixing at the molecular as well as the macroscopic level in shear flows is measured instantaneously by using two lasers and two cameras to excite and then detect LIF from NO and acetone simultaneously. Quantitative measurements of molecular mixing are of tremendous importance, particularly in chemically reacting systems, for which mixing of the fuel and oxidant streams at the molecular level is required to initiate reactions.

Magnetic Damping for Crystal Growth in Space
J. S. Walker*
National Aeronautics and Space Administration, NAG8-1453

Any crystal growth experiment in an earth-orbiting vehicle is subjected to chaotic accelerations called g-jitters. A magnetic field can be used to suppress the melt motions driven by g-jitters in order to achieve optimal crystal properties. Models are being developed for the magnetically damped melt motions and for the associated transport of dopants that determine the electrical properties of the crystal. Model predictions will be used to design magnet damping furnaces for experiments on the International Space Station.

Magnetic Stabilization of Thermocapillary Convection during Floating Zone Crystal Growth
J. S. Walker,* B. C. Houchens
National Aeronautics and Space Adminstration, NAG8-1453

In the floating zone process, there is a zone of molten semiconductor between a melting feed rod and a growing crystal. The thermocapillary convection is driven by the change of the temperature-dependent surface tension along the free surface of the floating zone. Floating zone crystal growth in space is very promising, but it is currently limited by an instability in the thermocapillary flow, leading to an oscillatory flow with adverse effects on the crystal. A magnetic field can be used to stabilize the flow and to eliminate the adverse effects of the oscillatory flow. Models are being developed to guide the selection of the optimal magnetic field.

Planar Visualization and Measurements of Axisymmetric, Supersonic Base Flows
J. C. Dutton,* C. J. Bourdon
U.S. Army Research Office, DAAG55-97-1-0122

Planar visualizations and measurements of the large-scale turbulent structures in axisymmetric, supersonic base flows are being obtained by means of Rayleigh/Mie scattering and planar laser-induced fluorescence (PLIF). We have obtained similar visualizations for planar, supersonic base flows, but the focus here is to investigate the extra rates of strain that occur in axisymmetric flows. In addition, the effects of afterbody boattailing and mass bleed into the separated region will be studied. Both of these flowfield manipulations are known to increase base pressure, but their effects on the detailed turbulent structure of the near wake are currently unknown.

Quantitative Visualization of Convective Heat and Mass Transfer in Complex Internal Flow
J. G. Georgiadis,* R. O. Buckius,* K. W. Moser, D. J. Holdych
National Science Foundation, CTS 95-21509; National Center for Supercomputing Applications

In applications with complex internal flows, it is the unpredictability of the tortuous fluid particle trajectories that produces enhanced heat and mass transfer, beyond the level of simple molecular diffusion. The research program consists of a combination of noninvasive measurements with magnetic resonance imaging (MRI) and numerical simulation using lattice-Boltzmann methods (LBM) of such internal flows. The key objectives are: (1) to develop a noninvasive methodology to probe convective transport in complex flows using a combination of MRI and LBM and (2) to understand and quantify the mechanisms of heat/mass transport enhancement in stirring processes.

Simultaneous Measurements of Pressure, Temperature, and Velocity Using CARS in High-Speed Flows
J. C. Dutton,* R. P. Lucht,* J. P. Kuehner
U.S. Army Research Office, DAAG55-97-1-0194

The objective of this research is the development and application of a new nonintrusive optical measurement technique for spatially and temporally resolved measurements of pressure, temperature, and velocity in high-speed flows. A high-resolution coherent anti-Stokes Raman scattering (CARS) technique will be developed. Pure rotational Raman resonances of the nitrogen molecule will be probed using CARS in a counterpropagating pump beam configuration. Velocity will be determined from the relative frequency shift between the pure rotational lines, and pressure and temperature from the resonance lineshapes and relative spectral intensities.

Simultaneous Pressure, Temperature, and Density Measurements Using CARS in High-Speed Flows
J. C. Dutton,* R. P. Lucht,* M. A. Woodmansee
U.S. Army Research Office, DAAH04-95-1-0276

The objective of this research program is the development and application of a new non-intrusive optical diagnostic technique for spatially and temporally resolved measurements of pressure, temperature, and density in high-speed flows. The high-resolution N2 CARS technique takes advantage of the line-broadening effects and population shifts of the rotational structure near the nitrogen (v=0?1) Q-branch, which are pressure- and temperature-sensitive. To extract the thermodynamic quantities from the high-resolution (Dw0.1 cm-1) CARS spectra, theoretical spectra are fit to the experimental spectra in a least-squares manner. Further, in this least-squares fit, pressure and temperature are left as adjustable parameters; density is then determined through the ideal gas equation-of-state.

Smart Mesoflaps for Aeroelastic Transpiration to Control Shock/Boundary-Layer Interactions
J. C. Dutton,* E. Loth* (Aero. & Astro. Engr.), D. L. Gefroh, E. S. Hafenrichter
Air Force Office of Scientific Research, F49620-98-1-0381; Defense Advanced Research Projects Agency, F49620-98-1-0490

This project investigates the feasibility and performance of a novel 'smart mesoflap' system to control the shock/bounday-layer interactions typical of supersonic mixed-compression inlets. In the experimental aerodynamics portion of this investigation, an array of flaps will be examined in a Mach 2.5 supersonic wind tunnel with a flow containing an oblique shock/boundary-layer interaction. Detailed flow diagnostics, including schlieren/shadowgraph photography, laser Doppler velocimetry, and pressure-sensitive paint, will be used to determine the effectiveness of the mesoflap system. Investigations of a normal shock interaction at Mach 1.45 will also be conducted.

Stability and the Transition to Three-dimensionality in Flows Past Axisymmetric Bluff Bodies
A. J. Pearlstein,* W. J. Mantle
National Science Foundation, CTS 94-22770

At low Reynolds numbers (Re), flow past axisymmetric bodies is steady, axisymmetric, and attached. For bluff bodies (e.g., spheres, raindrops, torpedoes), the flow separates as Re increases; ultimately, transition to unsteady, nonaxisymmetric flow occurs. We have studied this transition computationally for a fixed sphere; the steady, axisymmetric flow becomes unstable with respect to an oscillatory helical instability at Re = 175.1. The critical Re and predicted Strouhal number (dimensionless frequency) agree well with previous experiments. We are extending this work to the case where the body falls or rises freely under the action of gravity. In that case, the rigid body motion can couple to the flow disturbances, leading to a lower critical Re.

Stability of the Wake behind a Rotating Circular Cylinder
A. J. Pearlstein,* F. Petteni, L. Wang
University of Illinois

We are conducting computational investigations of the stability of the steady (asymmetric) 2-D flow past a rotating cylinder, as well as the time-periodic 2-D flow to which it loses its stability as the Reynolds number (Re) is increased. To date, we have shown that the critical Re at which the steady flow becomes unstable to 2-D disturbances depends nonmonotonically on the dimensionless rotation rate, and that the frequency of the critical mode that evolves from the Hopf bifurcation has several discontinuities along the stability boundary, corresponding to transitions from one mode to another.

Thermoelectric Effects during Semiconductor Crystal Growth with a Magnetic Field
J. S. Walker*
National Aeronautics and Space Administration, NAG8-1453

Single crystals composed of alloys of two semiconductors are important for devices to interface between optical and electrical signals. During the growth of these crystals from a liquid, temperature gradients produce voltage gradients that drive circulation of electric current through the liquid because of the nonuniform thermoelectric properties of the alloy. Strong magnetic fields are often applied during crystal growth in order to stabilize the liquid motion, and these magnetic fields interact with the thermoelectric currents to drive additional melt motions. Models are being developed to predict the thermoelectric effects during crystal growth with a strong magnetic field.

Three-dimensional Vortex Shedding from Circular Cylinders
S. P. Vanka,* G. Luo
U.S. Office of Naval Research, N00014-96-1-0697

We are studying the three-dimensional structure of vortex shedding from a circular cylinder placed in a spanwise sheared free stream. Computations are being performed using a high-order accurate numerical scheme and high performance parallel computers.

Three-dimensional, Supersonic Base Flows
J. C. Dutton,* B. A. Boswell
U.S. Army Research Office, DAAG55-97-1-0122

This project seeks to obtain nonintrusive, laser-based diagnostic measurements to identify the important flow mechanisms in three-dimensional base flows that are representative of high-speed objects flying at angle-of-attack. Important questions to be addressed include the steadiness of the overall flowfield, the interaction of the lee-side vortical flow with the base flow recirculation region, and the size and shape of the separated flow regions. Measurement methods used include schlieren/shadowgraph photography, surface streakline visualizations, LDV, planar Rayleigh/Mie scattering, pressure-sensitive paint, and PIV.

Void Fraction and Pressure Drop in Microchannels
T. A. Newell,* P. S. Hrnjak,* V. Nino, W. Payne
NSF I/UCRC Air Conditioning and Refrigeration Center

Void fraction and pressure drop of different microchannel tubes is being investigated. A variety of refrigerants at different mass flow rates and quality are examined.