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Particle Image Velocimetry (PIV) measurements in the wake of a cascade of compressor blades at stallQuesenbury, Robert C. 03 1900 (has links)
Approved for public release, distribution unlimited / The flow around second generation controlled-diffusion compressor blades in cascade at stall was examined through the use of a Particle Image Velocimeter (PIV). This examination was conducted from the trailing edge of the blade well into the wake region. Flow visualization techniques were used to observe and record the behavior of the region of flow separation. The PIV data showed that the separated regions continued to grow up to approximately 10% of blade chord length past the trailing edge. Past this point, these areas began to show signs of becoming entrained in the free stream. The flow visualization highlighted the extent of the backflow. The PIV measurements documented the velocity profiles within the wake region.
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An experimental investigation of a fighter aircraft model at high angles of attackLeedy, David Humbert 09 1900 (has links)
Approved for public release; distribution is unlimited / A low speed wind tunnel investigation was conducted to
examine the aerodynamic characteristics of the flowfield
around a three percent scale YF-17 lightweight fighter
prototype model at high angles of attack using flow
visualization and force and moment measurements. Smoke
filaments, injected into the wind tunnel test section, were
illuminated by a laser sheet to highlight flow phenomena
about the model. Force and moment measurements were made
using a precision six-component strain gage balance. The
investigation marked the first attempt at qualitative flow
analysis using the laser sheet flow visualization system
recently installed in the Naval Postgraduate School low speed
wind tunnel facility. The investigation was undertaken to
specifically identify flow phenomena and/or regions of
interest that may have bearing on the design and performance
of supermaneuverable aircraft. The data indicate a good
correlation between the observed flow phenomena and force and
moment measurements at various angles of attack, thus
establishing the credibility of such experimental
investigations for high angle of attack aerodynamic research. / http://archive.org/details/experimentalinve00leed / Lieutenant Commander, United States Navy
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Design of micromixer and microfludic control systemUnknown Date (has links)
Micromixer is one of the most significant components of microfluidic systems,
which manifest essential applications in the field of chemistry and biochemistry. Achieving
complete mixing performance at the shortest micro channel length is essential for a
successful micromixer design. We have developed five novel micromixers which have
advantages of high efficiency, simple fabrication, easy integration and ease for mass
production. The design principle is based on the concept of splitting-recombination and
chaotic advection. Numerical models of these micromixers are developed to characterize
the mixing performance. Experiments are also carried out to fabricate the micromixers
and evaluate the mixing performance. Numerical simulation for different parameters such
as fluids properties, inlet velocities and microchannel cross sectional sizes are also
conducted to investigate their effects on the mixing performance. The results show that
critical inlet velocities can be predicted for normal fluid flow in the micromixers. When the inlet velocity is smaller than the critical value, the fluids mixing is dominated by
mechanism of splitting-recombination, otherwise, it is dominated by chaotic advection. If
the micromixer can tolerate higher inlet velocity, the complete mixing length can be further
reduced. Our simulation results will provide valuable information for engineers to design
a micromixer by choosing appropriate geometry to boost mixing performance and broaden
implicational range to fit their specific needs. Accurate and complicated fluidic control,
such as flow mixing or reaction, solution preparation, large scale combination of different
reagents is also important for bio-application of microfluidics. A proposal microfluidic
system is capable of creating 1024 kinds of combination mixtures. The system is composed
of a high density integrated microfluidic chip and control system. The high density
microfluidic chip, which is simply fabricated through soft lithography technique, contains
a pair of 32 flow channels that can be specifically addressed by each 10 actuation channels
based on principle of multiplexor in electronic circuits. The corresponding hardware and
software compose the control system, which can be easy fabricated and modified,
especially for prototype machine developing. Moreover, the control system has general
application. Experiments are conducted to verify the feasibility of this microfluidic system
for multi-optional solution combination. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2013.
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A study of the mechanism for vortex breakdown and some measures for its controlJones, Michael Charles, 1971- January 2002 (has links)
Abstract not available
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A study of inverted wings with endplates in ground effectRicapito, David, Mechanical & Manufacturing Engineering, Faculty of Engineering, UNSW January 2007 (has links)
An inverted wing with various endplate configurations was investigated at two different angles of incidence. A moving ground was designed and constructed for use in the UNSW T1 wind tunnel. The test cases were investigated in ground effect using the moving ground. Measurements and observations were obtained using laser sheet flow visualisation and laser doppler anemometry. Computational fluid dynamics models of the test cases were run to gain further understanding of the flow field generated when using inverted wings with endplates. The computational fluid dynamics models correlated well to the experimental results.
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Quantitative flow visualization system for gas-liquid two phase flows /Hiscock, John E., January 2000 (has links)
Thesis (M.Eng.)--Memorial University of Newfoundland, 2000. / Restricted until November 2001. Bibliography: leaves 120-124.
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Dynamic behaviour of brain and surrogate materials under ballistic impactSoltanipour Lazarjan, Milad January 2015 (has links)
In the last several decades the number of the fatalities related to criminally inflicted cranial gunshot wounds has increased (Aarabi et al.; Jena et al., 2014; Mota et al., 2003). Back-spattered bloodstain patterns are often important in investigations of cranial gunshot fatalities, particularly when there is a doubt whether the death is suicide or homicide. Back-spatter is the projection of blood and tissue back toward the firearm. However, the mechanism of creation of the backspatter is not understood well. There are several hypotheses, which describe the formation of the backspatter. However, as it is difficult to study the internal mechanics of formation of the backspatter in animal experiments as the head is opaque and sample properties vary from animal to animal. Performing ballistic experiments on human cadavers is rarely not possible for ethical reasons. An alternative is to build a realistic physical 3D model of the human head, which can be used for reconstruction of crime scenes and BPA training purposes. This requires a simulant material for each layer of the human head. In order to build a realistic model of human head, it is necessary to understand the effect of the each layer of the human head to the generation of the back-spatter. Simulant materials offer the possibility of safe, well‐controlled experiments. Suitable simulants must be biologically inert, be stable over some reasonable shelf‐life, and respond to ballistic penetration in the same way as the responding human tissues. Traditionally 10-20% (w/w) gelatine have been used as a simulant for human soft tissues in ballistic experiments. However, 10-20% of gelatine has never been validated as a brain simulant. Moreover, due to the viscoelastic nature of the brain it is not possible to find the exact mechanical properties of the brain at ballistic strain rates. Therefore, in this study several experiments were designed to obtain qualitative and quantitative data using high speed cameras to compare different concentrations of gelatine and new composite material with the bovine and ovine brains. Factors such as the form of the fragmentation, velocity of the ejected material, expansion rate, stopping distance, absorption of kinetic energy and effect of the suction as well as ejection of the air from the wound cavity and its involvement in the generation of the backspatter have been investigated. Furthermore, in this study a new composite material has been developed, which is able to create more realistic form of the fragmentation and expansion rate compared to the all different percentage of the gelatine. The results of this study suggested that none of the concentrations the gelatine used in this study were capable of recreating the form of the damage to the one observed from bovine and ovine brain. The elastic response of the brain tissue is much lower that observed in gelatine samples. None of the simulants reproduced the stopping distance or form of the damage seen in bovine brain. Suction and ejection of the air as a result of creation of the temporary cavity has a direct relation to the elasticity of the material. For example, by reducing the percentage of the gelatine the velocity of the air drawn into the cavity increases however, the reverse scenario can be seen for the ejection of the air. This study showed that elastic response of the brain tissue was not enough to eject the brain and biological materials out of the cranium. However, the intracranial pressure raises as the projectile passes through the head. This pressure has the potential of ejecting the brain and biological material backward and create back-spatter. Finally, the results of this study suggested that for each specific type of experiment, a unique simulant must be designed to meet the requirements for that particular experiment.
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Rheological and Velocity Profile Measurements of Blood in Microflow Using Micro-particle Image VelocimetryPitts, Katie Lynn 22 April 2013 (has links)
Microhemodynamics is the study of blood
flow in small vessels, usually on the order of
50 to 100 µm. The in vitro study of blood
flow in small channels is analogous to the in
vivo study of the microcirculation. At this scale the Reynolds and Womersly numbers
are significantly less than 1 and the viscous stress and pressure gradient are the main
determinant of flow. Blood is a non-homogeneous, non-Newtonian fluid and this complex composition and behavior has a greater impact at the microscale. A key parameter is the shear stress at the wall, which is involved in many processes such as platelet activation,
gas exchange, embryogenesis and angiogenesis. In order to measure the shear rate in
these blood flows the velocity profile must be measured. The measured profile can be characterized by the maximum velocity, the flow rate, the shear rate at the wall, or a shape parameter reflecting the bluntness of the velocity profile.
The technique of micro-particle image velocimetry (µPIV) was investigated to measure the velocity profiles of blood microflows. The material of the channel, the type of tracer particles, the camera used, and the choice in data processing were all validated to improve the overall accuracy of µPIV as a blood microflow measurement method. The knowledge gained through these experiments is of immediate interest to applications such as the design of lab-on-a-chip components for blood analysis, analysis of blood flow behavior, understanding the shear stress on blood in the microcirculation and blood substitute analysis.
Polymer channels were fabricated from polydimethylsiloxane (PDMS) by soft lithography
in a clean room. PDMS was chosen for ease of fabrication and biocompatibility. The contacting properties of saline, water, and blood with various polymer channel materials
was measured. As PDMS is naturally hydrophilic, surface treatment options were explored. Oxygenated plasma treatment was found to be less beneficial for blood than for water.
The choice of camera and tracer particles were validated. Generally, for in vivo studies, red blood cells (RBCs) are used as tracer particles for the µPIV method, while for in vitro studies, artificial fluorescent micro particles are added to the blood. It is demonstrated here that the use of RBCs as tracer particles creates a large depth of correlation (DOC), which can approach the size of vessel itself and decreases the accuracy of the method. Next, the accuracy of each method is compared directly. Pulsed images used in conjunction with fluorescing tracer particles are shown to give results closest to theoretical approximations. The effect of the various post-processing methods currently available were compared for accuracy and computation time. It was shown that changing the amount of overlap in the post-processing parameters affects the results by nearly 10%. Using the greatest amount of correlation window overlap with elongated windows aligned with the flow was shown to give the best results when coupled with a image pre-processing method previously published for microflows of water.
Finally the developed method was applied to a relevant biomedical engineering problem: the evaluation of blood substitutes and blood viscosity modifiers. Alginate is a frequently used viscosity modifier which has many uses in industry, including biomedical applications. Here the effect of alginate on the blood rheology, i.e., the shape of the velocity profile and the maximum velocity of blood
flow in microchannels, was investigated. Alginate was found to blunt the shape of the velocity profile while also decreasing the shear rate at the wall.
Overall, the accuracy of µPIV measurements of blood flows has been improved by this thesis. The work presented here has extended the known methods and accuracy issues of blood flow measurements in µPIV, improved the understanding of the blood velocity profile behavior, and applied that knowledge and methods to interesting, relevant problems in biomedical and biofluids engineering.
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A study of inverted wings with endplates in ground effectRicapito, David, Mechanical & Manufacturing Engineering, Faculty of Engineering, UNSW January 2007 (has links)
An inverted wing with various endplate configurations was investigated at two different angles of incidence. A moving ground was designed and constructed for use in the UNSW T1 wind tunnel. The test cases were investigated in ground effect using the moving ground. Measurements and observations were obtained using laser sheet flow visualisation and laser doppler anemometry. Computational fluid dynamics models of the test cases were run to gain further understanding of the flow field generated when using inverted wings with endplates. The computational fluid dynamics models correlated well to the experimental results.
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Jet to jet impingement in a confined space /Tyagi, Ashok K. January 1997 (has links)
Thesis (Ph.D.) -- McMaster University, 1997. / Includes bibliographical references (p. 234-241). Also available via World Wide Web.
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