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Measurements of surface shear stresses under a three-dimensional turbulent boundary layer using oil-film laser interferometry /Ailinger, Kevin Gerard, January 1990 (has links)
Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 60-61). Also available via the Internet.
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Flow control in adverse pressure gradient using supersonic microjetsKumar, Vikas, Alvi, Farrukh S. January 2003 (has links)
Thesis (M.S.)--Florida State University, 2003. / Advisor: Dr. Farrukh S. Alvi, Florida State University, FAMU-FSU College of Engineering, Dept. of Mechanical Engineering. Title and description from dissertation home page (Aug. 27, 2004). Includes bibliographical references.
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Numerical investigation of transition control of a flat plate boundary layer.Kral, Linda Dee. January 1988 (has links)
A numerical model has been developed for investigating boundary layer transition control for a three-dimensional flat plate boundary layer. Control of a periodically forced boundary layer in an incompressible fluid is studied using surface heating techniques. The spatially evolving boundary layer is simulated. The Navier-Stokes and energy equations are integrated using a fully implicit finite difference/spectral method. The Navier-Stokes equations are in vorticity-velocity form and are coupled with the energy equation through the viscosity dependence on temperature. Both passive and active methods of control by surface heating are investigated. In passive methods of control, wall heating is employed to alter the stability characteristics of the mean flow. Both uniform and nonuniform surface temperature distributions are studied. In the active control investigations, temperature perturbations are introduced locally along finite heater strips to directly attenuate the instability waves in the flow. A feedback control loop is employed in which a downstream sensor is used to monitor wall shear stress fluctuations. Passive control of small amplitude two-dimensional Tollmien-Schlichting waves and three-dimensional oblique waves are numerically simulated with both uniform and nonuniform passive heating applied. Strong reductions in both amplitude levels and amplification rates are achieved. Active control of small amplitude two-dimensional and three-dimensional disturbances is also numerically simulated. With proper phase control, in phase reinforcement and out of phase attenuation is demonstrated. A receptivity study is performed to study how localized temperature perturbations are generated into Tollmien-Schlichting waves. It is shown that narrow heater strips are more receptive in that they maximize the amplitude level of the disturbances in the flow. It is also found that the local temperature fluctuations cause mainly a strong normal gradient in spanwise vorticity. Control of the early stages of the nonlinear breakdown process is also investigated. Uniform passive control is applied to both the fundamental and sub-harmonic routes to turbulence. A strong reduction in amplitude levels and growth rates results. In particular, the three-dimensional growth rates are significantly reduced below the uncontrolled levels. Active control of the fundamental breakdown process is also numerically simulated. Control is achieved using either a two-dimensional or three-dimensional control input.
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Layer-by-Layer Assembly of Clay-filled Polymer Nanocomposite Thin FilmsJang, Woo-Sik 14 January 2010 (has links)
A variety of functional thin films can be produced using the layer-by-layer
assembly technique. In this work, assemblies of anionic clay and cationic polymer were
studied with regard to film growth and gas barrier properties. A simple, yet flexible
robotic dipping system, for the preparation of these thin films, was built. The robot
alternately dips a substrate into aqueous mixtures with rinsing and drying in between.
Thin films of sodium montmorillonite clay and cationic polymer were grown and studied
on poly(ethylene terephthalate) film or a silicon wafer. After 30 clay polymer bilayers
were deposited, the resulting transparent film had an oxygen transmission rate (OTR)
below 0.005 cm3/m2/day/atm. This low OTR, which is unprecedented for a clay-filled
polymer composite, is believed to be due to a ?brick wall? nanostructure comprised of
completely exfoliated clay bricks in polymeric ?mortar?. The growth of polymer and clay
assemblies is then shown to be controlled by altering the pH of polyethylenimine (PEI).
Growth, oxygen permeability, and mechanical behavior of clay-PEI assemblies were
studied as a function of pH in an effort to tailor the behavior of these thin films. Thicker
deposition at high pH resulted in reduced oxygen permeability and lower modulus, which
highlights the tailorability of this system.
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Environmentally Benign Flame Retardant Nanocoatings for FabricLi, Yu-Chin 2011 May 1900 (has links)
A variety of materials were used to fabricate nanocoatings using layer-by-layer
(LbL) assembly to reduce the flammability of cotton fabric. The most effective
brominated flame retardants have raised concerns related to their toxicity and
environmental impact, which has created a need for alternative flame retardant
chemistries and approaches. Polymer nanocomposites typically exhibit reduced mass
loss and heat release rates, along with anti-dripping behavior, all of which are believed
to be due to the formation of a barrier surface layer. Despite these benefits, the viscosity
and modulus of the final polymeric material is often altered, making industrial
processing difficult. These challenges inspired the use of LbL assembly to create densely
layered nanocomposites in an effort to produce more flame-retardant coatings.
Laponite and montmorillonite (MMT) clay were paired with branched
poly(ethylenimine) to create thin film assemblies that can be tailored by changing pH
and concentration of aqueous deposition mixtures. Both films can be grown linearly as a
function of layers deposited, and they contained at least 70 wt percent of clay. When applying
these films to cotton fabric, the individual fibers are uniformly coated and the fabric has significant char left after burning. MMT-coated fabric exhibits reduced total heat release,
suggesting a protective ceramic surface layer is created.
Small molecule, POSS-based LbL thin films were also successfully deposited on
cotton fabric. With less than 8 wt percent added to the total fabric weight, more than 12 wt percent
char remained after microscale combustion calorimetry. Furthermore, afterglow time
was reduced and the fabric weave structure and shape of the individual fibers were
highly preserved following vertical flame testing. A silica-like sheath was formed after
burning that protected the fibers.
Finally, the first intumescent LbL assembly was deposited on cotton fabric. SEM
images show significant bubble formation on fibers, coated with a 0.5 wt percent PAAm/1
wt percent PSP coating after burning. In several instances, a direct flame on the fabric was
extinguished. The peak HRR and THR of coated fabric has 30 percent and 65 percent reduction,
respectively, compared to the uncoated control fabric. These anti-flammable
nanocoatings provide a relatively environmentally-friendly alternative for protecting
fabrics, such as cotton, and lay the groundwork for rendering many other complex
substrates (e.g., foam) flame-retardant without altering their processing and desirable
mechanical behavior.
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Analysis of mixing layer heights inferred from radiosonde, wind profiler, airborne lidar, airborne microwave temperature profiler, and in-situ aircraft data during the Texas 2000 air quality study in Houston, TXSmith, Christina Lynn 29 August 2005 (has links)
The mixing layer (ML) heights inferred from radiosondes, wind profilers,
airborne lidar, airborne microwave temperature profiler (MTP), and in-situ aircraft data
were compared during the Texas 2000 Air Quality Study in the Houston area. The
comparisons and resulting good agreement between the separate instruments allowed for
the spatial and temporal evolution of the ML height distribution to be determined across
the Houston area on September 1, 2000.
A benchmark method was created for determining ML heights from radiosonde
data. The ML heights determined using this method were compared to ML heights
determined using wind profiler data. The airborne lidar and MTP heights were also
compared to the wind profiler heights. This was the first time the MTP was used for
estimating ML heights. Because of this, the MTP heights were also compared to the ML
heights determined by in-situ aircraft data.
There was good agreement between the ML estimates when the instruments were
co-located. The comparisons between the benchmark method and the wind profilers
were independent of the quality of the profiler heights. The statistics for lidar and the
wind profilers were better for the inland profiler comparisons. Even so, the results for
coastal profilers were similar to the other comparisons. The results between the MTP
and the wind profilers were comparable with the results found between the other
instruments, and better, in that the statistics were similar for the both the inland and
coastal profilers. The results between the MTP and in-situ aircraft data provided
additional support for the use of MTP for determining ML heights.
The combination of the inland and coastal wind profilers with the airborne
instruments provided adequate information for the spatial and temporal evolution of the
ML height to be determined across the Houston area on September 1, 2000. By
analyzing the ML height distribution, major features were evident. These features
included the shallow ML heights associated with the marine air from Galveston Bay and
the Gulf of Mexico, and the sharp gradient of increasing ML heights north of Houston
associated with the variation in the inversion depth found on this day.
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Layer-by-layer assembly of electrically conductive polymer thin filmsJan, Chien Sy Jason 17 September 2007 (has links)
Layer-by-layer (LbL) assembly was used to produce highly conductive thin films
with carbon black (CB) and polyelectrolytes. The effects of sonication and pHadjustment
of the deposition mixtures on the conductivity and transparency of deposited
films were studied. Drying temperature was also evaluated with regard to thin film
resistance. Sonication and oven drying at 70oC produced films with the lowest sheet
resistance (~ 1500 é/sq), which corresponds to a bulk resistivity of 0.2 éâÂÂ
cm for a 14-
bilayer film that is 1.3 üm thick. Increasing the pH of the PAA-stabilized mixture and
decreasing the pH of the PEI-stabilized mixture resulted in films with 70% transparency
due to thinner deposition from increased polymer charge density. Varying the number
of bilayers allows both sheet resistance and optical transparency to be tailored over a
broad range.
Variation of deposition mixture composition led to further reduction of sheet
resistance per bilayer. A 14 bilayer film, made from mixtures of 0.25wt% carbon black
in 0.05wt% PAA and plain 0.1wt% PEI, was found to have a sheet resistance of
approximately 325 é/sq. Bulk resistivity was not improved due to the film being 8 üm
thick, but this combination of small thickness and low resistance is an order of magnitude better than carbon black filled composites made via traditional melt or
solution processing. Applications for this technology lie in the areas of flexible
electronics, electrostatic charge dissipation, and electromagnetic interference shielding.
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An experimental study of coherent structures in a three-dimensional turbulent boundary layer /Ha, Siew-Mun, January 1993 (has links)
Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 70-74). Also available via the Internet.
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Investigation of separation and reattachment of a turbulent shear layer flow over a backward-facing step /Kim, Jeongbin John. January 1978 (has links)
Thesis (Ph. D.)--Stanford University, 1978. / "Printed in 2003 by digital xerographic process on acid-free paper"--P. after T.p. Includes abstract (p. iv). Includes bibliographical references (p. 213-217). Also issued in print.
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Investigation of separation and reattachment of a turbulent shear layer flow over a backward-facing step /Kim, Jeongbin John. January 1978 (has links)
Thesis (Ph. D.)--Stanford University, 1978. / "Printed in 2003 by digital xerographic process on acid-free paper"--P. after T.p. Includes abstract (p. iv). eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (p. 213-217).
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