Scientific and Technical Aerospace Reports Volume 39 April 6, 2001

we have examined the dynamical behavior and stability of a variety of liquid bridge configurations with emphasis on bridges that
are held between coaxial circular supports, although liquid configurations in partially filled containers are also considered. The
poster presentation will summarize our experimental, theoretical and numerical work on the stability and dynamics of liquid
bridges, with particular emphasis on nonaxisymmetric bridges and axisymmetric bridge configurations that lose stability to nonaxisymmetric
perturbations.
Author (revised)
Dynamic Stability; Liquid Bridges; Interfacial Tension; Numerical Stability
20010024964 Michigan Univ., Dept. of Aerospace Engineering, Ann Arbor, MI USA
Droplet Formation by Vortex Rings
Kim, Choongil, Michigan Univ., USA; Bernal, Luis P., Michigan Univ., USA; Proceedings of the Fifth Microgravity Fluid Physics
and Transport Phenomena Conference; December 2000, pp. 1280-1282; In English; See also 20010024890; No Copyright; Abstract
Only; Available from CASI only as part of the entire parent document
An experimental investigation of droplet formation by vortex rings impinging normal to a liquid/air or a liquid/liquid interface
has been conducted. Experiments included microgravity drop tower tests and 1-G tests to determine the effect of Weber number,
Reynolds number, as well as density ratio, and viscosity ratio on the interaction. Microgravity is an ideal environment to experimentally
study the dynamics of fluid interfaces. of particular interest is the dynamics of droplet formation by vortical flows under
surface tension controlled dynamics. These flow phenomena arise in a wide variety of engineering problems both in space systems
and on Earth. For example, liquid atomization is an important component of many systems including: aerosol generators for drug
delivery, fuel injectors, paint sprays, and inkjet printers. In these applications surface tension is the dominant stabilizing force of
the liquid interface because the drop size is very small. In microgravity, these flow processes can be studied at much larger scale
which facilitates experimental observation. The interaction of a vortex ring with the interface between immiscible fluids is a relatively
simple flow configuration where the phenomena of liquid breakup and droplet formation can be studied in controlled experiments.
The microgravity experiments were conducted in the 2.2 s drop tower at NASA Glenn Research Center. The drop tower
rig was equipped with a fluid test cell (15 cm # 15 cm # 300 cm) and a piston-type vortex ring generator attached to the bottom
of the test cell. The piston diameter is 1.9 cm. The fluid interface was stabilized with a knife-edge. The flow was visualized using
flat panel light source and a standard format video camera. For the drop tower experiments a control box detects the release of
the drop tower rig and initiates the vortex ring motion and timing lights shown in all the video recordings. The 1-G experiments
were conducted in the same rig. One of the main focus of the research is to determine the effects of density and viscosity ratio.
The tests results show two very distinct behaviors. At very small density and viscosity ratio, for a gas/liquid interface ratio, the
interaction results in a long liquid column that breaks into one or more small droplets at both ends of the column as illustrated.
The diameter of the droplets is significantly less than the initial vortex ring diameter. In this case change of the liquid viscosity
does not change the flow evolution significantly. In contrast, for a density ratio of order one, i.e. liquids of matched density, the
vortex ring propagates through the interface and forms a droplet and smaller secondary droplets as illustrated. The droplet shape
is approximately spherical and, the dye patterns inside the droplet indicate that the fluid inside the droplet carries some vorticity
from the initial vortex ring. For density ratio of order one, the effect of viscosity ratio is to change the size and structure of the
liquid column during droplet formation and the number and size of satellite droplets formed. These effects are characterized in
terms of the Ohnesorge number defined as Oh = mu(sub 1)/(rho(sub 1)(sigma)D)(sup 0.5). As the Ohnesorge number is increased,
the liquid column thickness becomes thinner and the duration of lower fluid column within the upper layer fluid is shorter as
shown. These results suggest that density and viscosity ratio effects are more important than previously recognized in computational
and experimental studies of multiphase flows.
Author (revised)
Experimentation; Drop Towers; Drop Size; Vortex Rings; Liquid-Liquid Interfaces; Liquid-Vapor Interfaces; Liquid Atomization
20010024965 Washington Univ., Dept. of Chemical Engineering, Seattle, WA USA
Thermophoretic Force Measurements on Single Spherical and Nonspherical Particles
Davis, E. James, Washington Univ., USA; Zheng, Feng, Washington Univ., USA; Proceedings of the Fifth Microgravity Fluid
Physics and Transport Phenomena Conference; December 2000, pp. 1283-1285; In English; See also 20010024890; No Copyright;
Abstract Only; Available from CASI only as part of the entire parent document
Thermophoretic forces (TF) play important roles in many areas including microparticle transport phenomena under microgravity
conditions. However, to our knowledge no experimental study has been done on the dependence of thermophoretic force
on particle shape. We have measured the thermophoretic force on two- and three-sphere aggregates, as well as single spheres of
polystyrene latex (PSL) particles in nitrogen gas in the transition regime (Knudsen number 0.1 to 10). Our data indicate that particle
aggregation may be accelerated by thermophoresis. Wang and Davis have successfully used an electrodynamic balance
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