Effect of Pipe Size in Two-Phase Flow
T. J. Hanratty,* B. Woods, L. Pan, E. Hurlburt
U.S. Department of Energy, DE-FG02-86ER13556

The influence of pipe diameter on flow regime transitions and on the modeling of stratified, slug, and annular flows is being studied. Two flow facilities are available. One has horizontal pipes with diameters of 1 in., 2 in., and 4 in. The other is a vertical system with pipes of 3/8 in., 3/4 in., and 1 1/2 in. Accomplishments include the development of a theory to predict the transition from stratified to slug flow, the development of an interpretation of entrainment measurements for annular flow in terms of the fundamental rate processes, the development of an understanding of the wave patterns in stratified flow, and the use of photographic and immersion methods to determine drop size in annular flow.

Wall Turbulence
T. J. Hanratty,* R. J. Adrian,* D. Heist, Z. C. Liu, M. Warholic, D. Papavassiliou, W. Sulzby
National Science Foundation, CTS 92-00936 (In conjunction with the Department of Theoretical and Applied Mechanics)

Laboratory and supercomputer experiments are being used to understand the structure of turbulence close to a wall. Highly organized flows are being identified that are responsible for the sustaining of wall turbulence. The effect of external influences, such as pressure gradients, drag-reducing agents, micelles, and imposed flow oscillations, on these structures is being studied. New photographic techniques (PIV) are being exploited to obtain simultaneous measurements at as many as 12,000 points.

Turbulent Flow Over Wavy Surfaces
T. J. Hanratty,* M. Warholic, Y. Na, D. Heist
National Science Foundation, CTS 92-00936

Turbulent flow over wavy surfaces is being studied both in the laboratory and by a direct numerical simulation. A particular emphasis during the year is the separated region that exists for large-amplitude waves. This well-defined separation bubble is being studied to provide the physical understanding needed to compute and control separated flows. The flow in the separated region is highly three-dimensional and seldom resembles the pattern indicated by the time-averaged streamlines. Work has been initiated to study the effect of waves on heat transfer and the effect of a moving wavy wall.

Mechanics of Suspensions
J. J. L. Higdon,* E. Guckel, M. Viera
Mobil Corp.

Concentrated suspensions of microscopic particles are encountered throughout the chemical process industry. The goal of this project is to characterize the rheology and sedimentation behavior of these systems, with special attention given to suspensions with nonhydrodynamic interparticle forces and particles of nonspherical shape, e.g., fibers and platelets. We are developing novel computational algorithms for large-scale many-body simulations to investigate these systems. Our methods follow the basic approach of the well-known Stokesian dynamics algorithm, but yield an operational count O(N) as opposed to the O(N3) effort of the traditional approach.

Inertial, Viscous, and Acoustic Effects on Drop Displacement Processes
J. J. L. Higdon,* P. Dimitrakopoulos, D. Graham
National Science Foundation, CTS 95-22724

The displacement of a fluid bubble or droplet from a solid substrate is an important phenomenon in a variety of processes ranging from enhanced oil recovery to precision coating operations. In this project, we are investigating the yield conditions for droplet displacement in both the viscous and inertial regimes. Additional studies are being conducted to assess the effect of fluctuating pressure fields associated with acoustic waves. Numerical computations are performed using finite-element and spectral boundary element techniques.

Rheology and Structure of Liquid Foams
J. J. L. Higdon,* E. Metsi
American Chemical Society, Petroleum Research Fund

Liquid-liquid or liquid-gas foams exhibit an interesting range of rheological behavior including yield stresses, wall slip, and stress discontinuities. In addition, the structure and length scales of a foam undergo continuous evolution under the action of shear. The goal of this project is to develop efficient algorithms for the simulation of foam rheology. These algorithms require detailed resolution of the microscopic fluid flows within a large-scale system which captures the disorder and range of length scales present in realistic foam flows.

Rheology in a Potential Vortex
W. R. Schowalter,* K. Sarkar
University of Illinois; Monsanto Co.

Vortex flows offer a special flow history for viscoelastic materials because of the revolution of principal axes of strain rate without a corresponding rotation of the fluid. We have computed the pulsating shape of a viscoelastic drop in a potential vortex. Phase differences between principal axes of the deformed drop and principal axes of strain rate provide new insights pertinent to rheology of complex fluids. We hope to relate the results to the unusual behavior of complex fluids in turbulent flows.

Solvation Forces in Protein Crystallization
C. F. Zukoski,* D. Rosenbaum, M. Farnum, E. Kokkoli
National Aeronautics and Space Administration, NAG 8-976

Manipulating the tertiary structures of proteins is crucial to many biological technologies. X-ray diffraction is the technique of choice to gain such insight. However, proteins are notoriously difficult to crystallize and, as a result, data on tertiary structures remain limited. In this study, we investigate protein/protein interactions mediated by the solvent to learn better how to induce crystallization. Our work focuses on using continuous phase chemical potential as a variable in controlling the ordering process.

Effect of Free Polymer on Protein Interaction Potentials
C. F. Zukoski,* A. Kulkarni
National Aeronautics and Space Administration, NAG 8-976

Protein crystals are often produced through the addition of soluble polymers to protein suspensions. In this study, the effects of polymer molecular weight and concentration on the strength of protein interactions is investigated. An unexpected minimum in protein solution second virial coefficient is observed. This phenomenon is intimately related to polymer depletion forces and polymer density fluctuations resulting from the proximity of a polymer solution phase boundary.