Code UG Weekly Notes 9-26-01

Physical Sciences Division
Weekly Highlights for Week Ending 9/26/2001)

** Indicates item is appropriate for the HQ senior staff
and may appear on the OBPR Web site:
http://SpaceResearch.nasa.gov

GENERAL

FOUR NEW HIRES IN BIOFLUIDS/BIOFLUIDS SENSORS AT GRC: Four scientists
recently joined the Microgravity Fluid Physics Branch of Microgravity
Science Division at NASA Glenn in biofluid mechanics and biofluid sensors
area. Dr. Rafat R. Ansari earned his Ph.D. in Biophysics from the University
of Guelph and University of Waterloo, Onatrio, Canada. Dr. Patricia Parsons
has a PhD in Biochemical Engineering Department of Chemical Engineering
from The Johns Hopkins University. Dr. David Fischer earned his MS in
EE from the Johns Hopkins University and Ph.D. in Optics from the University
of Rochester. Dr. Gregory Zimmerli has a PhD in Physics from the Pennsylvania
State University. They bring a broad range of expertise that include:
novel fiber-optic light scattering sensors and their use in studying phenomena
in fluid physics and biological sciences; novel model of angiogenesis
(the growth of new blood vessels) in the quail embryo; two-photon microscopy
and fluctuation correlation spectroscopy applicable for imaging and characterization
of biological samples; optical coherence Tomography for biocrystal growth
studies and tissue structure determination; and three-dimensional near-field
microscope for intracellular imaging, high-resolution cell adhesion studies
and biofilm measurements.

SHUTTLE FLIGHT PROGRAM

** SMOLDERING COMBUSTION GASCAN (MSC) RETURNS USEFUL DATA ON STS-105:
The GRC team retrieved the first of two reflight payloads of the MSC experiment,
payload G-774, at Kennedy Space Center the week of September 10, 2001.
It had flown as a Get-Away Special (GAScan) experiment aboard the STS-105
and returned in good condition. All indications are that the hardware
functioned as designed. G-774 had two polyurethane foam test sections;
one had forward flow of the oxidizer gas (in the direction of burn), the
other opposed. Both test section polyurethane foam pieces (the fuel) were
ignited. Glenn Research Center team of civil servants and contractors
downloaded the data successfully. Of special interest was the Ultrasonic
Imaging System (UIS), as this was its first test in space to "see"
the smolder front as it traversed the test pieces. The research team has
so far given a favorable report for the data.

Glenn Research Center team of civil servants and contractors built both
G-774 and G-775 units. During the same September 10th week, the team also
delivered and successfully integrated payload G-775 at KSC. It is to fly
aboard the Shuttle Endeavor, STS-108 (UF-1), scheduled for November 29,
2001, completing the reflight series.

The investigation on Microgravity Smoldering Combustion (MSC), led by
Prof. A. Carlos Fernandez-Pello of UC, Berkeley, has the objective of
validating the model for theoretical predictions of smolder propagation
in order to enhance our understanding of the smolder hazard. Smoldering
combustion is the initiation mode for many accidental fires and consequently,
is responsible for the loss of many lives. The NASA PAO commented on the
fact that some forty per cent of all household fires are started by smoldering
furniture. The possibility of a smoldering fire on a spacecraft is of
particular concern because the smolder fire could go undetected for a
considerable time.

ISS FLIGHT PROGRAM

PHYSICS OF COLLOIDS IN SPACE (PCS) ON ISS: After being powered on following
EXPRESS Rack 2’s successful "return to service" on Wednesday
(9/19/01), EXPPCS initiated a 72 hour run. During this run, EXPPCS has
re-homogenized the AB6 and AB13 binary colloid samples and has re-initiated
our detailed diagnostic runs on them. We had to restart the detailed runs
on AB6 and AB13 because important science had been missed by being powered
down (and not able to run our diagnostics on these crystallizing samples)
during last week’s national tragedy and failure of the 9/13/01 EXPRESS
Rack 2 software load.

DELTA PRELIMINARY DESIGN REQUIREMENTS REVIEW (?PDR) RESCHEDULED FOR LTMPEF:
The LTMPE Project ?PDR review will be used to evaluate the capability
of the Low Temperature Microgravity Physics Experiments Facility (LTMPEF)
preliminary design to meet the payload performance, interface, safety,
science and operations requirements, and to obtain agreement and approval
for the proposed design approach. The review will be performed on 27-8
September 2001 at the Old Pasadena Courtyard by Marriott hotel.

SCIENCE HIGHLIGHTS

COMBUSTION SCIENCE:

NUMERICAL STUDY OF BUOYANCY AND DIFFERENTIAL DIFFUSION EFFECTS ON TRIPLE
FLAMES: The objective of this study, led by Prof. J.-Y. Chen of UC Berkeley,
is to investigate numerically the influence of gravity and differential
diffusion on the structure and dynamics of triple flames with inert dilution.
An improved understanding of flame ignition and stabilization will lead
to better control strategies in suppressing accidental fires. First, an
existing Direct Numerical Simulations (DNS) code of turbulent combustion
is modified for modeling two-dimensional triple flames. Results from the
inviscid linear instability analysis of triple flames with/without gravity
effects have been further analyzed. Fourier analysis of the temperature
history at a fixed location was conducted. As the triple flame is unstable,
only a limited time series data is computed before the flame leaves the
computational domain. A preliminary examination of the possible unstable
mechanisms leading to the movement of triple flames downstream has been
conducted by studying the quantity (Vfx-U) in the axial direction where
Vfx is the triple flame propagation speed in the axial direction. The
results show that for a unstable triple flame the flame propagation speed
is smaller than local fluid velocity during most of the time. In addition,
a plot of (Vfx-U) against the inclination angle of the triple flame with
respect to the centerline shows that triple flame propagation speed in
the axial direction component is greatly reduced by the inclination angle.
The corresponding results for a triple flame with initially unstable condition
but without gravity show the reverse trends as the flame becomes stable.

FLUID PHYSICS:

MISCIBLE DROPLETS IN A POROUS MEDIUM AND THE EFFECTS OF KORTEWEG STRESSES:
Fluid Physics PI Prof. Meiburg (University of California at Santa Barbara,
Santa Barbara) presented numerical simulation results for the displacement
of a drop in a porous medium. The drop is surrounded by a more viscous
fluid with which it is fully miscible. The simulations are based on a
set of augmented HeleShaw equations that account for nonconventional,
so-called Korteweg stresses resulting from locally steep concentration
gradients. Globally, these stresses tend to stabilize the displacement.
However, there are important distinctions between their action and the
effects of surface tension in an immiscible flow. Since the Korteweg stresses
depend on the concentration gradient field, the effective net force across
the miscible interface region is not just a function of the drop’s geometry,
but also of the velocity gradient tensor. Locally high strain at the leading
edge of the drop generates steep concentration gradients and large Korteweg
stresses. Around the rear of the drop, the diffusion layer is much thicker
and the related stresses smaller. The drop is seen to form a tail, which
can be explained based on a pressure balance argument similar to the one
invoked to explain tail formation in HeleShaw flows with surfactant. The
dependence of such flows on the Peclet number is complex, as steeper concentration
gradients amplify the growth of the viscous fingering instability, while
simultaneously generating larger stabilizing Korteweg forces. These results
are reported in the following paper:
Ching-Yao Chen, Lilin Wang, and Eckart Meiburg "Miscible droplets
in a porous medium and the effects of Korteweg Stresses," Physics
Of Fluids Volume 13, Number 9 September 2001

A PERTURBATION ANALYSIS OF THE STABILITY OF LONG LIQUID BRIDGES BETWEEN
ALMOST CIRCULAR SUPPORTING DISKS: Fluid Physics PI Prof. Alexander (National
Center for Microgravity Research on Fluids and Combustion, Case Western
Reserve University) consider the stability of an isothermal liquid mass
of constant properties (density and surface tension) held by capillary
forces between two solid disks placed a distance L apart (the so-called
liquid bridge model). For a weightless liquid bridge that is a right circular
cylinder, the well-known Rayleigh stability limit holds, and the liquid
column becomes unstable when its length is larger than its circumference.
Many perturbations from this ideal configuration have been studied in
the past, but the supporting disk shape has always been assumed circular.
In this Brief Communication the influence of noncircular supports on stability
limits of almost cylindrical liquid bridges is analyzed through an asymptotic
analysis. Closed form expressions for the stability limits are presented.
The results obtained show that when a noncircular disk is the only effect
considered the maximum stable length of the column is reduced (as one
could expect) but when it is combined with other nonsymmetric effects,
the maximum stable length of the bridge depends on the combination of
the different effects considered, and there can be situations in which
the resulting configuration is more stable than it would be with only
one perturbation. This happens when two non-symmetric effects act simultaneously
with opposite senses. When both disks are equal in shape (either circular
or non-circular), to the leading order considered here, the stability
limit does not change no matter the relative orientation of one of the
disks with respect to the other. Higher approximations should be considered
to elucidate how this twisting effect affects (marginally) the liquid
bridge stability. These results are reported in the following paper:
J. Meseguer, J. M. Perales and J. I. D. Alexander "A perturbation
analysis of the stability of long liquid bridges between almost circular
supporting disks," Physics Of Fluids Volume 13, Number 9 September
2001

UPCOMING EVENTS

September 27-8, 2001 Delta PDR for the Low Temperature Microgravity Research
Facility, Old Pasadena Courtyard by Marriott Hotel, Pasadena, CA

October 14-18, 2001, 17th Interdisciplinary Laser Science Conference,
Long Beach Convention Center
Long Beach, CA

March 18-22, 2002, 2002 American Physical Society March Meeting, Indianapolis,
IN

April 20-23, 2002, 2002 American Physical Society April Meeting, Albuquerque,
NM

April 22-25 2002 , 2002 Applied Computational Research Society Joint
Meeting, Computational Micro And Nano Technology, International Conference
on Computational Nano Science, Modeling & Simulation of Microsystems,
San Juan Marriott Resort, San Juan, Puerto Rico http://www.cr.org

Additional meetings and symposia can be found at: http://microgravity.grc.nasa.gov/ugml/ugmltext.htm