Thesis (Ph. D.)--University of Iowa, 2007. / Supervisor: Gregory Carmichael. Includes bibliographical references (leaves 129-136).

No description available.

Thesis--Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution. / Includes bibliographical references (p. 181-186).

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Boundary layer ingesting (BLI) propulsion systems offer potential fuel burn reduction for civil aviation and synergize with new advanced airframe concepts. However, the distorted inlet flow for BLI systems can cause performance and stability margin loss. System level analyses generally size a single engine at a fixed design point which ignores the distributed nature of many BLI architectures. Furthermore, operability and performance during o design are generally not considered during the sizing process. In this thesis, a methodology is developed for multi-design point sizing of BLI propulsion systems for specific vehicle geometry including an operability constraint. The methodology is applied to a 300 passenger hybrid-wing body vehicle with embedded turbofan engines. The methodology required investigations into three main areas of research. The first was the modeling of BLI impacts over a range of flight conditions. A BLI analysis tool was developed which models the vehicle boundary layer, pre-entry region, inlet, and fan losses throughout the entire flight envelope. An experiment investigating the impact of the modeling approach is conducted, and results show that proper mapping of the fan, inlet, and BLI propulsive benefit is crucially important for making proper design decisions. The impact of BLI on the system was found to vary significantly during o ff design and especially with changes in vehicle angle of attack. The operability constraint is investigated using a parallel compressor model and was found to place a minimum limit on the propulsor height. The second area of investigation was the creation of a multi-propulsor sizing methodology which accounts for diff erences between propulsors during flight that is induced by their interaction with the vehicle. A modified multi-design point approach was used which employs a set of design and power management rules to relate the operation of the propulsors. A performance comparison of this methodology with the standard single propulsor approach showed a signicant difference. The final area of investigation was the determination of critical o ff-design conditions for the sizing procedure. A screening process is developed which tests all off -design conditions for a subset of the design space to find conditions which are stall margin or thrust deficient. The experiment showed that it is necessary to consider the high angle of attack take-off condition during sizing for the HWB vehicle and that a variable area nozzle is required to meet the operability constraint. A follow on experiment showed that the inclusion of this point reduced the achievable fuel burn benefit for more aggressive BLI designs.Boundary layer ingesting (BLI) propulsion systems offer potential fuel burn reduction for civil aviation and synergize with new advanced airframe concepts. However, the distorted inlet flow for BLI systems can cause performance and stability margin loss. System level analyses generally size a single engine at a fixed design point which ignores the distributed nature of many BLI architectures. Furthermore, operability and performance during o design are generally not considered during the sizing process. In this thesis, a methodology is developed for multi-design point sizing of BLI propulsion systems for specific vehicle geometry including an operability constraint. The methodology is applied to a 300 passenger hybrid-wing body vehicle with embedded turbofan engines. The methodology required investigations into three main areas of research. The first was the modeling of BLI impacts over a range of flight conditions. A BLI analysis tool was developed which models the vehicle boundary layer, pre-entry region, inlet, and fan losses throughout the entire flight envelope. An experiment investigating the impact of the modeling approach is conducted, and results show that proper mapping of the fan, inlet, and BLI propulsive benefit is crucially important for making proper design decisions. The impact of BLI on the system was found to vary significantly during o ff design and especially with changes in vehicle angle of attack. The operability constraint is investigated using a parallel compressor model and was found to place a minimum limit on the propulsor height. The second area of investigation was the creation of a multi-propulsor sizing methodology which accounts for diff erences between propulsors during flight that is induced by their interaction with the vehicle. A modified multi-design point approach was used which employs a set of design and power management rules to relate the operation of the propulsors. A performance comparison of this methodology with the standard single propulsor approach showed a signicant difference. The final area of investigation was the determination of critical o ff-design conditions for the sizing procedure. A screening process is developed which tests all off -design conditions for a subset of the design space to find conditions which are stall margin or thrust deficient. The experiment showed that it is necessary to consider the high angle of attack take-off condition during sizing for the HWB vehicle and that a variable area nozzle is required to meet the operability constraint. A follow on experiment showed that the inclusion of this point reduced the achievable fuel burn benefit for more aggressive BLI designs.

abstract: In the last few years, significant advances in nanofabrication have allowed tailoring of structures and materials at a molecular level enabling nanofabrication with precise control of dimensions and organization at molecular length scales, a development leading to significant advances in nanoscale systems. Although, the direction of progress seems to follow the path of microelectronics, the fundamental physics in a nanoscale system changes more rapidly compared to microelectronics, as the size scale is decreased. The changes in length, area, and volume ratios due to reduction in size alter the relative influence of various physical effects determining the overall operation of a system in unexpected ways. One such category of nanofluidic structures demonstrating unique ionic and molecular transport characteristics are nanopores. Nanopores derive their unique transport characteristics from the electrostatic interaction of nanopore surface charge with aqueous ionic solutions. In this doctoral research cylindrical nanopores, in single and array configuration, were fabricated in silicon-on-insulator (SOI) using a combination of electron beam lithography (EBL) and reactive ion etching (RIE). The fabrication method presented is compatible with standard semiconductor foundries and allows fabrication of nanopores with desired geometries and precise dimensional control, providing near ideal and isolated physical modeling systems to study ion transport at the nanometer level. Ion transport through nanopores was characterized by measuring ionic conductances of arrays of nanopores of various diameters for a wide range of concentration of aqueous hydrochloric acid (HCl) ionic solutions. Measured ionic conductances demonstrated two distinct regimes based on surface charge interactions at low ionic concentrations and nanopore geometry at high ionic concentrations. Field effect modulation of ion transport through nanopore arrays, in a fashion similar to semiconductor transistors, was also studied. Using ionic conductance measurements, it was shown that the concentration of ions in the nanopore volume was significantly changed when a gate voltage on nanopore arrays was applied, hence controlling their transport. Based on the ion transport results, single nanopores were used to demonstrate their application as nanoscale particle counters by using polystyrene nanobeads, monodispersed in aqueous HCl solutions of different molarities. Effects of field effect modulation on particle transition events were also demonstrated. / Dissertation/Thesis / Ph.D. Electrical Engineering 2011

Properties of textiles have great influences on the thermo-physiological and skin sensorial wear comfort of the human body. Sportswear is expected to have good moisture management property, which is key factor to achieve wear comfort. For some sports, they are also expected to have low friction with skin and antibacterial capability. To meet these demands, single-layer fabrics are utterly incompetent. Thus, model dual-layer textiles that consist of a thin hydrophobic electrospun inner layer and a thick hydrophilic electrospun outer layer are designed and fabricated to verify the possibility to simultaneously achieve dual functionalities, including good moisture transport property, with low friction with skin or good antibacterial property. The hydrophobic inner layer ensures low water absorption and transmission of sweat via capillary motion, while the hydrophilic outer layer draws the sweat out from the inner layer and facilitates evaporation to the surrounding environment. In the PhD work presented in this thesis, electrospun nanofibrous mats are used as the model textiles because they have large specific surface area due to a lot of interpenetrating pores between the nanofibers, which could facilitate both the capillary motion and effect of surface modification and incorporation of functional materials. Also, to let the moisture transport away fast, fairly thin hydrophobic inner layers could be achieved by electrospinning because it could control the thickness accurately. To improve the moisture transport property, the capillary motion in the textile is facilitated by decreasing the pore size or increasing the surface hydrophilicity. Dual-layer mats composed of a thick layer of hydrophilic polyacrylonitrile (PAN) nanofibers and a thin layer of hydrophobic polystyrene (PS) nanofibers with and without interpenetrating nanopores are fabricated respectively. Then the mats are coated with polydopamine (PDOPA) to different extents to tailor the water wettability of the PS layer. It is found that with a large quantity of nanochannels, the porous PS nanofibers exhibit a stronger capillary effect than the solid PS nanofibers. The capillary motion in the porous PS nanofibers can be further enhanced by slight surface modification with PDOPA while retaining the large hydrophilicity difference between the two layers, inducing a strong push-pull effect to transport water from the PS to the PAN layer. To lower the friction between the textile and skin, both of the hydration of the skin and the chemical component of textiles are modified. Core-shell nanofibers with a PAN-rich core and a poly (vinylidene fluoride) (PVDF)-rich shell are fabricated by single-spinneret electrospinning and used as the inner layer of the dual-layer mats. The dual-layer textile has good moisture transport property and the inner layer of the textile has lower friction with the skin, because the PAN in the inner layer could increase the wettability of the layer, thus improve the capillary effect, and the PVDF-rich shell could lower the friction between the textile and the skin. The synergistic combination of a considerably hydrophobic PAN/PVDF inner layer and a highly hydrophilic CA outer layer induces a strong push-pull effect, resulting in efficient moisture-wicking. To introduce antibacterial property to the dual-layer textile, zinc oxide (ZnO) NPs were covalently attached on the surface of the ethoxysilane-functionalized cross-linked PVDF inner layer. The results of related testes show that the incorporation of the ZnO NPs could render the textile antibacterial property as well as enhance the water wettability of the inner, thus the moisture transport property of the textile is also strongly improved. Also, the ZnO NPs show very good anti-wash property due to the covalent bonding with the inner layer. Thus the potential health risk caused by the detachment of the NPs could be avoided. In summary, the research results presented in this thesis provide effective strategies to enhance the capillary motion and moisture transport property of the textile, as well as achieve dual functionalities. The design concepts demonstrated in this PhD research can be used as model systems for development of novel multifunctional textiles in industries.

Test sections in laboratory studies should be fully developed and uniform if they are to be generalized. The objective of this study is to develop a model for predicting the uniform flow development length (Lunif) in a rough laboratory flume as a function of hydraulic parameters and bed particle roughness height (ks). Using an ADV time-averaged point velocity was measured in developing and fully developed turbulent subcritical rough open-channel flows. A series of laboratory tests were carried out in a 6.1-m-long and 0.46-m-wide rectangular channel. Tests were conducted with fine gravel (d50 = 5.8 mm, ks = 3.1d90 = 0.026 m), medium gravel (d50 = 14 mm, ks = 0.068 m), and with fine /medium gravel (d50 = 11 mm, ks = 0.04 m). For each test, longitudinal point velocity measurements were made along the center of the channel at five elevations, and at thirteen longitudinal stations. The study concluded that for flow to be uniform, the flow depth and mean cross-sectional velocity must be constant. In addition, root mean square of the fluctuating component of the velocity, RMS(u'), which is the measure of the turbulence intensity, should be uniform in order for a flow to consider uniform. Thus, RMS(u') is one of the indicative measures for determining the location where the developing flow is fully developed and uniform. The results showed that increasing the bed roughness height decreases the uniform flow development length. Using the dimensional and statistical analyses Lunif was estimated as a linear function of Reynold's particle number and Froude number.

Transition of the attachment fine boundary layer was investigated using a large swept cylinder. Results for natural transition and transition tripping with two-dimensional trip wires were simila to those obtained by Poll using a similar, but smaller, model. ]Lower displacement thickness Reynolds numbers but larger trip sizes, than for the flat-plate boundary layer, were required for transition. The investigation of transition tripping was then extended to involve three-dimensional trips. The attachment line boundary layer was less susceptible to three-dimensional trips than to two-dimensional trips but upper and lower bounds of attachment line Reynolds number for transition were identical. It was also found that the roughness Reynolds numbers for fully effective three-dimensional trips were similar for the attachment line and flat-plate boundary layers. Another common feature was the more abrupt upstream movement of the transition front with increasing Reynolds number for three-dimensional trips than for two-dimensional trips. Turbulence spreading downstream of a three-dimensional trip was also examined and, as in the flat-plate boundary layer, was found to be heavily dependent on Reynolds number (varying from 3° at low Reynolds number to a value approaching 10° as Reynolds number exceeded the value for natural transition), but was also dependent on either the trip size or the initial conditions at which the trip first introduced turbulent spots. The effects of higher levels of freestrearn turbulence were then investigated for both two-dimensional and three-dimensional trips. With a small increase in freestrea turbulence the conditions for transition with twodimensional trips were affected far more than those for three-dimensional trips, for which only the transition completion conditions were affected signfficantly, resulting in a reduced extent ofthe transition region. Larger levels of turbulence appeared to have similar effects on the two trip types. Restrictions in model length and windspeed for the higher turbulence tests prevented an accurate investigation of the effects of turbulence,on the upper and lower bounds for transition tripping and on the influence of spanwise distance at higher levels of turbulence. Finally, the interaction between two trips positioned on the attachment line was examined. The effect of the second trip on the transition Reynolds number was found to a function of the streamwise separation distance between the two trips.

An experimental parametric sturdy of vane and air-jet vortex generators in a turbulent boundary layer has been carried out. Experiments were carried out in two facilities, one with a free-stream velocity of 20 m/s and a boundary layer thickness (6) of 41.5 mm, and one in a high speed facility at free-stream Mach numbers of between 0.45 and 0.75 and a boundary layer thickness of 20 mm. Cross-stream data were measured at a number of downstream locations using a miniature five-hole pressure probe, such that local cross-stream velocity vectors could be derived. Streamwise vorticity was calculated using the velocity vector data. In the low speed study, vortex generator parameters were as follows: ' Vane vortex generators: thin rectangular vanes with a vane aspect ratio of unity (2h/c = 1), free-stream velocity 20 m/s, incidence (cc = 10', 15', 18', 20'), height-to-boundary- layer- thickness-ratio (h/8 0.554,0.916,1.27,1.639), and strearnwise distance from the vortex generator (x/6 = 3.855,12.048,19.277,26.506). ' Air-jet vortex generators: circular jet nozzles, free-stream velocity = 20 m/s, jet nozzle pitch and skew angles (cc, P= 30', 45', 60'), hole diameter-to-boundary-layer-thickness-ratio (D/5 = 0.098,0.193,0.289), jet-to-free-stream-velocity ratio (VR = 0.7,1.0,1.3,1.6,2.0), and strearnwise distance from the vortex generator (x/8 = 3.855,12.048,19.277,26.506). In the high-speed study, the vortex generator parameters were as follows: Vane vortex generators: thin rectangular vanes with an aspect ratio of unity, incidence ((X 1505 20'), he i ght-to- boundary- I ayer-th i ckne s s-rati o (h/8 = 0.75), strearnwise distance from the vortex generator (x/6 = 8.755 16.25,23.75), and free-stream Mach numbers of 0.45,0.6 and 0.75. Air-jet vortex generators: jet pitch ((x = 30', 45'), jet skew angle (P = 30', 45', 60'), hole diameter-to-boundary-layer-thickness-ratio (D/8 = 0.15,0.3), j et-to- free- strearn-ve loc ity ratio (VR = 1.6), and strearnwise distance from the vortex generator (x/6 = 8.75,16.25,23.75, 31.25), and free-stream Mach numbers of 0.50,0.6 and 0.75. Streamwise vorticity data from the experiment was used to generate prediction techniques that would allow the vorticity profiles, downstream of vane or air-jet vortex generators, to be predicted. Both techniques are based on the approximation of the experimental cross-stream vorticity data to Gaussian distributions of vorticity through the vortex centre. The techniques, which are empirically derived, are simple equations that give the peak vorticity and vortex radius based on the vortex generator parameters. Use of these descriptors allows the assembly of the Gaussian vorticity equation. Both techniques are compared with the experimental data set and were seen to produce peak vorticity results to within 12% and 20% (for the vanes and air-jets respectively), 15% for the radius of the vortex, and 15% and 20% in vortex circulation (for the vanes and air-jets respectively). The two simple prediction techniques allow good prediction of the vortex structure at extremely low computational effort.