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Objectives:
To study the formation
and dispersion of a diesel fuel in water emulsion in a confined tank.Two
flow models are considered: 1) entrainment
due to the impingement of an interface with a vertical jet,
2) entrainment of droplets
due to shear between the fuel and water layers. Dispersion
and emulsion stability in isotropic turbulence are also considered.
Motivation
This research is
motivated by the desire of the United States Navy to minimize environmental
discharge of small quantities of fuel that results when refilling compensated
fuel tanks.Many combatant ships
use compensated fuel tanks (arranged in a series) that fill with seawater
from the bottom as fuel is withdrawn from the top, dramatically improving
seaworthiness.This experimental
research is being fed into numerical analysis being performed separately.
Impingement
Mechanism
Principal
Investigator:
Pete
Friedman
The formation and
dispersion of fuel droplets in water due to the impingement of an interface
with a jet has been experimentally investigated with an impingement test
chamber (Figure
1).The macroscopic
flow structure around the interaction between the jet and the interface
has been analyzed and is published in Friedman
and Katz (1999). Flow
behavior is classified into four flow regimes as a function of Richardson
number and to a lesser extent Reynolds number (Figure
2).In flow regime
1, the jet slightly deforms the interface but remains attached (Figure
3).Flow regime 2
occurs when the flow separates at the edge of the interfacial deformation(Figure
4).In flow regime
3, the cavity becomes unstable and alternately collapses and reforms (Figure
5).Flow regime 4
(not shown) occurs when the jet penetrates through to the upper tank wall.Entrainment
mechanisms including the conditions or onset of entrainment (Figure
6) and the resulting emulsion properties—most notably droplet
diameters have been analyzed as a function of flow conditions (sample shown
in Figure
7) and fluid properties (Figure
8) and submitted for publication in Friedman
et al (in review). The data collapse nicely as shown in
(Figure
9).
Although this research
is motivated by the relatively narrow problem of an interface between immiscible
fluids impinged with a jet, many of the conclusions have a far broader
application.One study result, the
depth of penetration from the jet has particularly broad application.A
penetration depth correlation for a diverse set of systems (Figure
10) has been submitted for publication in Friedman
and Katz (in review).Future
work will focus on understanding the dispersion and stability of the emulsion
created.Part of the investigation
is to determine the behavior of droplets in isotropic turbulence.Droplets
with a velocity on the order of the velocity of the turbulent fluctuations
tend to remain in solution and be transported.
Shear
Mechanism
Principal
Investigator:
Xiongjun Wu
The
entrainment of droplets due to the shear at an immiscible fluid interface
is being studied in a shear test facility (Figure
11).Since
Kelvin expanded Helmholtz’s theoretical study into stratified shear flow
with layers of different densities, substantial number of studies, both
theoretical and experimental, have been conducted to understand the mechanism
of entrainment and mixing of stratified shear flows. However most of these
studies have concentrated on miscible stratified shear flows. In contrast
to the relatively well established physics of the miscible stratified shear
flows, in which droplet formation and its subsequent dynamics are not a
major issue, our understanding of the immiscible stratified shear flows,
especially those with substantial changes in density and viscosity, is
incomplete.To date we have determined
the flow structure (Figure
12), vorticity distributions (sample shown in Figure
13), and droplet
formation mechanisms using PIV (Figure
14) and published
these results in Wu and
Katz (1999).Additional
results including droplet size distributions inside, above and below the
mixture layer (Figure
15,Figure
16and Figure
17) have been analyzed
and are being prepared for publication.
The
shear problem has applications beyond the current research. Stratified
shear flows occur in a wide range of situations on various scales, from
the large-scale geophysical flows such as deepening of upper-ocean mixed
layer, thickening of sediment suspension layer, and growth of planetary
boundary layer to the small-scale engineering flows such as oil spills,
discharge of buoyant thermal jet from power plant and combustible mixtures
in internal combustion engines.
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Impingement publications:
Friedman,
P. D. and Katz, J., 1999, “The Flow and Mixing Mechanisms Caused by the
Impingement of an Immiscible Interface with a Vertical Jet,” Physics
of Fluids, Vol. 11, pp. 2598-2606.
Friedman,
P. D. and Katz, J., “Rise Height for Negatively Buoyant Fountains and Depth
of Penetration for Negatively Buoyant Jets Impinging an Interface,” To
Be Published.
Friedman,
P. D., Winthrop, A. L. and Katz, J., “Droplet Formation and Size Distributions
From an Immiscible Interface Impinged with a Negatively Buoyant Jet,” To
Be Published.
Shear Publications:
Wu,
X. and Katz, J., 1999, “On the Flow Structures and Mixing Phenomenon in a Fuel/Water Stratified Shear Flow,” Proceedings, 3rd ASME/JSME
Joint Fluids Engineering Conference, July 18-23, 1999, San Francisco,
Ca.
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