The hot gas temperature in gas turbine engines is far above the permissible metal temperatures. Advanced cooling technologies must be applied to cool the blades, so they can withstand the extreme conditions. Film cooling is widely used in modern high temperature and high pressure blades as an active cooling scheme. In this study, the film cooling effectiveness in different regions of gas turbine blades was investigated with various film hole/slot configurations and mainstream flow conditions. The study consisted of four parts: 1) effect of upstream wake on blade surface film cooling, 2) effect of upstream vortex on platform purge flow cooling, 3) influence of hole shape and angle on leading edge film cooling and 4) slot film cooling on trailing edge. Pressure sensitive paint (PSP) technique was used to get the conduction-free film cooling effectiveness distribution. For the blade surface film cooling, the effectiveness from axial shaped holes and compound angle shaped holes were examined. Results showed that the compound angle shaped holes offer better film effectiveness than the axial shaped holes. The upstream stationary wakes have detrimental effect on film effectiveness in certain wake rod phase positions. For platform purge flow cooling, the stator-rotor gap was simulated by a typical labyrinth-like seal. Delta wings were used to generate vortex and modeled the passage vortex generated by the upstream vanes. Results showed that the upstream vortex reduces the film cooling effectiveness on the platform. For the leading edge film cooling, two film cooling designs, each with four film cooling hole configurations, were investigated. Results showed that the shaped holes provide higher film cooling effectiveness than the cylindrical holes at higher average blowing ratios. In the same range of average blowing ratio, the radial angle holes produce better effectiveness than the compound angle holes. The seven-row design results in much higher effectiveness than the three-row design. For the trailing edge slot cooling, the effect of slot lip thickness on film effectiveness under the two mainstream conditions was investigated. Results showed thinner lips offer higher effectiveness. The film effectiveness on the slots reduces when the incoming mainstream boundary layer thickness decreases.

Thorough understanding of interfaces requires an assessment of both the surface and bulk properties through the use of multiple techniques. In this thesis, infrared absorption, Raman scattering and sum frequency generation were used as vibrational probes of different features of interfacial systems including the ability to measure surface and bulk effects. Two-dimension correlation analysis was used to study the relationship between the spectral response of the different techniques. Attenuated total reflection absorption, bulk Raman scattering and sum frequency generation were used to study the adsorption of ethanol--water mixture on fused silica. With the use of two-dimension correlation analysis, interesting results were observed concerning the behavior of the surface in respect to the bulk. Surface concentration of ethanol were concluded to be higher than in the bulk indicative of competitive adsorption. Furthermore, at low concentration ethanol was shown to adsorb to the surface in dimers, to then form a bilayer of strongly oriented ethanol molecules at higher concentration. At highest concentration, this bilayer is disturbed, leaving only one layer at the surface of oriented ethanol molecules. The same spectroscopic techniques were applied to pressure sensitive adhesives of different composition while drying on a sapphire surface. The presence or absence of acrylic acid in the material was shown to alter the reorientation at the surface while drying. In the case where no acrylic acid is present, the orientation of the polymer at the surface was driven by the packing of the molecules at the surface. When acrylic acid was present in the pressure sensitive adhesive, reorientation occurred much faster and was caused by strong hydrogen bonding with the surface of the sapphire. An increase in acrylic acid composition, increased the rate of reorientation. An experimental set up was constructed to specifically study interfaces with a nonuniform distribution within the plane of the surface. This allows for concomitant measurement of polarized total internal reflection Raman scattering and sum frequency generation spectroscopy along with bright field imaging and cross polarized imaging. This set up was used to study the L-histidine crystal in situ adsorbed on fused silica. The polarized experiments along with calculations allowed for a more in-depth analysis of the crystal orientation effect on the birefringence, the Raman and the sum frequency generation. / Graduate

d-Limonene (Lim) was used in various polymer formulations to achieve a more sustainable polymerization. Lim is a renewable and essentially non-toxic compound, derived from citrus fruit peels, that may replace some of the many toxic and fossil-based chemicals used in polymer synthesis. Bulk free-radical polymerizations of n-butyl acrylate (BA) with Lim were performed to investigate Lim co-polymerization kinetics and estimate the monomer reactivity ratios, important parameters in the prediction of copolymer composition. Kinetic modeling of the BA/Lim copolymerization was performed with PREDICI simulation software. The model supports the presence of a significant degradative chain transfer reaction due to Lim. This reaction mechanism is due to the presence of allylic hydrogen in Lim. Nonetheless, relatively high molecular weight polymers were produced. It was concluded that Lim behaves more like a chain transfer agent than a co-monomer. Terpolymerizations of BA, butyl methacrylate (BMA) with Lim were then performed. In order to predict the terpolymer composition, the monomer reactivity ratios for BA/BMA were estimated. By applying the three pairs of co-monomer reactivity ratios to the integrated Mayo-Lewis equation, terpolymer compositions were ably predicted up to high monomer conversion levels. Lim was then used as a chain transfer agent to prepare core-shell latex-based pressure sensitive adhesives (PSA) comprising BA and styrene via seeded semi-batch emulsion polymerization. By varying the concentration of Lim and divinylbenzene crosslinker, the core polymer microstructure was modified to yield different molecular weights and degrees of crosslinking. The core latex was then used as a seed to prepare core-shell latexes. By changing the Lim concentration during the shell-stage polymerization, the molecular weight of shell polymer was also modified. The latexes were characterized for their microstructure and were cast as films for PSA performance evaluation. The PSA performance was shown to be highly related to the polymer microstructure. Tack and peel strength showed a decrease with increasing Lim concentration. Shear strength went through a maximum with a core Lim concentration increase from 0 to 5 phm.

Cellulose nanocrystals (CNCs) are attractive nanomaterials due to their superior mechanical properties, renewability, and natural abundance. Their surface hydroxyl groups, along with surface charges induced during their production, allow CNCs to be easily dispersed in an aqueous medium, especially with sustainable water-based production methods such as emulsion polymerization. Moreover, their surface functionality makes them highly suitable for modification, thereby making them even more versatile. Emulsion polymer latexes are heterogeneous mixtures, having a continuous aqueous phase along with a dispersed organic phase. Latex polymers are used in a wide range of applications such as in coating and adhesive films. Because of the bi-phasic nature of emulsion polymerizations, the surface properties of CNCs play a crucial role in their location relative to the organic phase, and how well-dispersed they are in the cast films. In this thesis, three grades of CNCs (Celluforce Inc.) with either hydrophilic, partially-hydrophobic, or hydrophobic surface properties, were combined with conventional emulsion and miniemulsion polymer formulations to investigate their effect on the properties of pressure sensitive adhesive (PSA) films. In the first instance, hydrophilic CNCs were tested in a seeded semi-batch emulsion polymerization. Using a sequential experimental design, the effects of polar comonomer, surfactant, chain transfer agent, and CNC loading on latex stability and PSA properties were studied. By increasing polymer chain entanglements and the work of adhesion, the hydrophilic CNCs were observed to simultaneously improve the three key properties of acrylic-based PSA films, i.e., tack, peel strength and shear strength. In the second part of this project, we compared the role of hydrophilic and partially-hydrophobic CNCs in PSA property modification. Viscosity measurements and atomic force microscopy revealed differences in the degree of association between the two types of CNCs and the latex particles. Dynamic strain-sweep tests showed that hydrophilic CNC nanocomposites softened at lower strains than their partially-hydrophobic counterparts. This behaviour was confirmed via dynamic frequency tests and modelling of the nanocomposites’ storage moduli, which suggested the formation of CNC aggregates of, on average, 3.8 and 1.3 times the length of CNCs. These results confirmed that the partially-hydrophobic CNCs led to improved CNC dispersion in the PSA films and ultimately, enhanced PSA properties. In the third part of the project, mini-emulsion polymerization (MEP) was used to embed the hydrophobic CNCs within the polymer particles in contrast to the hydrophilic and partially-hydrophobic CNCs which resided mainly in the aqueous phase or near the water-particle interface. Higher CNC loadings led to increased particle size, decreased polymerization rate and number of particles, while only slightly increased the viscosity and the work of adhesion. PSA film properties decreased upon the incorporation of hydrophobic CNCs. Transmission electron microscopy showed that CNCs were expelled from the latex particles at higher loadings, suggesting the incompatibility of the acrylic polymer and the CNCs’ modifying agents. The ability to modify CNCs enables one to achieve a range of hydrophilicity/hydrophobicity. This makes them extremely versatile in a heterogeneous mixture such as in an emulsion polymerization. Because emulsion polymers are used in a wide range of applications with a broad spectrum of properties (i.e., not only as adhesives but as non-tacky coatings), our ability to control CNC location relative to the polymer particles in the latex opens the door to a world of high value-added sustainable polymer products.

A new pressure-measurement technique which employs the tools of molecular spectroscopy has recently received considerable attention in the fluid mechanics community. Measurements are made via oxygen-sensitive molecules attached to the surface of interest as a coating, or paint. The pressure-sensitive-paint (PSP) technique is now commonly used in stationary wind-tunnel tests; this thesis presents the extension of the technique to advanced turbomachinery applications. New pressure- and temperature-sensitive paints (TSPs) have been developed for application to a state-of-the-art transonic compressor where pressures up to 2 atm and surface temperatures up to 140° C are expected for the first-stage rotor. PSP and TSP data has been acquired from the suction surface of the first-stage rotor of a transonic compressor operating at its peak-efficiency condition. The shock structure is clearly visible in the pressure image, and visual comparison to the corresponding computational fluid dynamics (CFD) prediction shows qualitative agreement to the PSP data. / Master of Science

No description available.

A numerical analysis of the loop tack test is presented to study the behavior of the strip and the influence of several factors, and the results are compared with experimental ones. The numerical results can be applied to model the performance of a pressure sensitive adhesive (PSA). Since the simulation of the loop tack test includes geometrical and material nonlinearities, it is solved numerically by the finite element method. The finite element program ABAQUS is used throughout the research. As the teardrop shaped loop is pushed down onto the adhesive and then pulled up, the variation of the loop behavior is investigated using two-dimensional (2D) and three-dimensional (3D) models. A bilinear elastic-plastic constitutive law is used for the strip. The deformation of the pressure sensitive adhesive is approximated as uniaxial extension of independent adhesive strands. A Winkler-type nonlinear elastic foundation and a viscoelastic foundation are used to model the PSA. A nonlinear elastic spring function is used, which is composed of a compression region for the bonding phase and a tension region for the debonding phase. A debonding failure criterion is assumed, in which an adhesive strand will debond when it reaches a certain length. During the bonding phase, it is assumed that the loop is perfectly bonded, and the contact time is not included. Curves of the pulling force versus the top displacement (i.e., tack curves) are obtained throughout the simulation. A parametric study is made with respect to the nonlinear spring function parameters, experimental uncertainties, and strip thickness. Anticlastic bending behavior is shown in the 3D analysis, and the contact patterns are presented. The effects of the elasticity modulus of the PSA for the elastic foundation and the displacement rate for the viscoelastic model are investigated. / Ph. D.

The loop tack test measures the tack (instant grip) of an adhesive. An analytical model of this test seems to be lacking and is the subject of this research. The strip is investigated using several mathematical formulations, and the solutions are obtained numerically. The loop is created from a flexible elastic strip that is bent into a teardrop shape, with its ends clamped together. The strip is tested in a cycle, in which the loop is first pushed onto the surface, compressing the adhesive. Then the loop is pulled up, and gradually debonds from the substrate. The loop is assumed to be nonlinearly elastic and inextensible. The mechanics of the loop tack test are studied in order to determine the impact of various factors on adhesive performance. These factors include the stiffness of the backing, the stiffness and thickness of the adhesive, the elongation of the adhesive before debonding, and the contact time. The relationship between the applied force and the vertical deflection of the loop's ends is determined, as well as that between the applied force and the contact length. Also, the maximum "pull - off" force needed to remove the substrate from the loop is obtained from the results. Shapes of the loop during the cycle are found. This research will increase understanding of the behavior of the adhesive and backing during the loop tack test. With the computer model that has been developed, any set of parameters and conditions can be analyzed, and improvements can be made in the test procedure. / Master of Science

Experimental studies have shown that the yield strength of many important engineering materials such as polymers, ceramics and metallic glasses is dependent on hydrostatic stress. In addition, these materials may also exhibit plastic dilatancy. These deviations from the assumptions of classical plasticity theories have also been observed for some metallic alloys, although to a lesser extent compared to non-metals. In pressure independent plastic solids, it has been found that the level of crack tip constraint can affect the near-tip stress and deformation fields and hence the fracture resistance. The objective of the present work is to study the effects of pressure sensitive yielding, plastic dilatancy and constraint loss on the ductile fracture processes under mode-I conditions. Further, the three-dimensional (3D) structure of elastic-plastic near-crack front fields in a pressure independent plastic solid under mixed mode (combined modes I and II) loading is also examined. A finite element study of 3D crack tip fields in pressure sensitive plastic solids under mode-I, small scale yielding (SSY) conditions is first carried out. The material is assumed to obey a small strain, Extended Drucker-Prager (EDP)yield criterion. The roles of pressure sensitive yielding, plastic dilatancy and yield locus shape on the 3D plastic zone development and near-crack front fields are systematically investigated. It is found that while pressure sensitivity leads to a significant drop in the hydrostatic stress all along the 3D crack front, it enhances the plastic strain and crack opening displacements. However, plastic incompressibility results in elevation of both near-tip hydrostatic stress and notch opening. The implications of these observations on micro-void growth and interaction near a notch tip are studied in detail subsequently. The effects of constraint loss on void growth near a notch tip under mode-I loading in materials exhibiting pressure sensitive yielding and plastic dilatancy are investigated by performing large deformation elastic-plastic finite element analyses. To this end, two-dimensional (2D)plane strain and 3Dmodified boundary layer formulations are employed by prescribing the elastic K-T field as remote boundary conditions. The results are generated for different combinations of K (or J ) and T -stress. The material is assumed to obey a finite strain, EDP yield condition. The distributions of hydrostatic stress and plastic strain in the ligament connecting the notch and a nearby void (cylindrical or spherical) as well as the growth of the notch and the void are studied. The results show that void growth with respect to J is enhanced due to pressure sensitivity, and more so when the plastic flow is non-dilatational, which corroborates with the trends exhibited by the 3D crack tip fields. However, the evolution of ductile fracture processes like void growth, plastic strain localization and ligament length reduction with respect to J is retarded in the case of spherical voids. Further, irrespective of pressure sensitivity, loss of crack tip constraint can significantly slow down void growth. The effects of pressure sensitive yielding and plastic dilatancy on near-tip void growth and multiple void interaction mechanisms in single edge notched bend (SENB) and center cracked tension (CCT) specimens which display high and low constraint levels, respectively, are investigated next. It is observed that the latter mechanism which is favored by high initial porosity is further accelerated by pressure sensitive yielding and high constraint. The predicted resistance curves based on a simple void coalescence mechanism show enhancement in fracture resistance when constraint level is low and when pressure sensitivity is suppressed. Finally, detailed elastic-plastic finite element simulations are carried out using a boundary layer (SSY) formulation to investigate the 3D nature of near-crack front fields in a von Mises solid under mixed mode (combined modes I and II)loading. The plastic zones and radial, angular and thickness variations of the stresses are studied corresponding to different levels of remote elastic mode mixity and applied load, as measured by the plastic zone size with respect to the plate thickness. The 3D results are compared with those obtained from 2D simulations and asymptotic solutions to establish the validity of 2D plane stress and plane strain approximations near a crack front. It is found that, in general, plane stress conditions prevail at a distance from the crack front exceeding half the plate thickness, although it could be slightly smaller for mode-II predominant loading.

The motion of shock waves is important in many fields of engineering and increasingly so with medical applications and applications to inertial confinement fusion technologies. The flow structures that moving shock waves create when they encounter a change in area is complex and can be difficult to understand. Previousresearchers have carried out experimental studies and many numerical studies looking at this problem in more detail. There has been a discrepancy between numerical and experimental work which had remained unanswered. One of the aims of this project is to try and resolve the discrepancy between numerical and experimental work and try to investigate what experimental techniques are suitable for work of this type and the exact way in which they should be applied. Most previous work has focused on sharp changes in geometry which induce immediate flow separation. In this project rounded corners will also be investigated and the complex flow features will be analyzed.Two geometries, namely a sharp 172 degree knife-edge and a 2.8 mm radius rounded corner will be investigated at three experimental pressure ratios of 4, 8 and 12 using air as the driver gas. This yields experimental shock Mach numbers of 1.28, 1.46 and 1.55. High-speed schlieren and shadowgraph photography with varying levels of sensitivity were used to qualitatively investigate the wave structures. Particle image velocimetry (PIV), pressure-sensitive paint (PSP) and traditional pressure transducers were used to quantify the flow field. Numerical simulations were performed using the commercial package Fluent to investigate the effect of numerical schemes on the flow field produced and for comparison with the experimental results. The sharp geometry was simulated successfully using an inviscid simulation while the rounded geometry required the addition of laminar viscosity. Reynolds number effects will be only sparsely referred to in this project as the flows under investigation show largely inviscid characteristics. As the flow is developing in time rather than in space, quotation of a distance-based Reynolds number is not entirely appropriate; however, Reynolds number based on the same spatial location but varying in time will be mentioned. The density-based diagnostics in this project were designed to have a depth of field appropriate to the test under consideration. This approach has been used relatively few times despite its easy setup and significant impact on the results. This project contains the first quantative use of PIV and PSP to shock wave diffraction. Previous studies have almost exclusively used density-based diagnostics which, although give the best impression of the flow field, do not allow for complete analysis and explanation of all of the flow features present. PIV measurements showed a maximum uncertainty of 5% while the PSP measurements showed an uncertainty of approximately 10%.The shock wave diffraction process, vortex formation, shear layer structure, secondary and even tertiary expansions and the shock vortex interaction were investigate. The experimental results have shown that using one experimental technique in isolation can give misleading results. Only by using a combination of experimental techniques can we achieve a complete understanding of the flow field and draw conclusions on the validity of the numerical results. Expanding the range of the experimental techniques currently in use is vital for experimental aerodynamic testing to remain relevant in an industry increasingly dominated by numerical research. To this end, significant research work has been carried out on extending the range of the PSP technique to allow for the capture of shock wave diffraction, one of the fastest transient fluid processes, and for applications to low-speed flow (< 20 ms−1).