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 ;f2 in., ;f7 in., and 1;f6 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 methods to determine drop size in annular flow. A new phenomenon of hindered droplet turbulence has been discovered.

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, miscelles, 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 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.

Gas absorption at an interface is of considerable interest in environmental and processing problems. It is controlled by flow fluctuations in the liquid in a region of about 200 microns thickness close to the interface. These fluctuations are greatly enhanced when waves are present. Experiments are being conducted to understand this process. A technique involving oxygen quenching of fluorescence is used to study the concentration field close to the interface. Optical methods are being developed to map out the instantaneous spatial variation of wave slope.

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( N ;s3) effort of the traditional approach.

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.

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.

Stokesian dynamics is being used to show the perturbations possible when a colloidal dispersion contains a few particles with a radius different from an otherwise monodisperse system. From the results we hope to explain the well known order/disorder transitions that occur when nominally monodisperse systems are subjected to increasing shear rates.

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.