In a gas turbine engine, turbine blades are exposed to temperatures above their melting point. Film-cooling and internal cooling techniques can prolong blade life and allow for higher engine temperatures. This study examines a novel cooling technique called a microcircuit, which combines internal convection and pressure side injection on a turbine blade tip. Holes on the tip called dirt purge holes expel dirt from the blade, so other holes are not clogged. Wind tunnel tests are used to observe how effectively dirt purge and microcircuit designs cool the tip. Tip gap size and blowing ratio are varied for different tip cooling configurations. Results show that the dirt purge holes provide significant film cooling on the leading edge with a small tip gap. Coolant injected from these holes impacts the shroud and floods the tip gap reducing tip leakage flow. With the addition of a microcircuit, coolant is delivered to a larger area of the tip. In all cases, cooling levels are higher for a small tip gap than a large tip gap. Increased blowing ratio does not have a dramatic effect on microcircuit film-cooling at the midchord but does improve internal cooling from the microcircuit. While the combined dirt purge holes and microcircuit cool the leading edge and midchord areas, there remains a small portion of the trailing edge that is not cooled. Also, results suggest that blowing from the microcircuit diminishes the tip leakage vortex. Overall, the microcircuit appears to be a feasible method for prolonging blade life. / Master of Science

Gas turbine blades are subject to harsh operating conditions that require innovative cooling techniques to insure reliable operation of parts. Film-cooling and internal cooling techniques can prolong blade life and allow for higher engine temperatures. This study examines several unique methods of cooling the turbine blade tip. The first method employs holes placed directly in the tip which inject coolant onto the blade tip. The second and third methods used holes placed on the pressure side of a blade near the tip representative of two different manufacturing techniques. The fourth method is a novel cooling technique called a microcircuit, which combines internal convection and injection from the pressure side near a turbine blade tip. Wind tunnel tests are used to observe how effectively these designs cool the tip through adiabatic effectiveness measurements and convective heat transfer measurements. Tip gap size and blowing ratio are varied for the different tip cooling configurations. Results from these studies show that coolant injection from either the tip surface or from the pressure side near the tip are viable cooling methods. All of these studies showed better cooling could be achieved at small tip gaps than large tip gaps. The results in which the two different manufacturing techniques were compared indicated that the technique producing more of a diffused hole provided better cooling on the tip. When comparing the thermal performance of all the cooling schemes investigated, the added benefit of the internal convective cooling shows that the microcircuit outperforms the other designs. / Master of Science

Cooling of turbine parts in a gas turbine engine is necessary for operation as the temperature of combustion gases is higher than the melting temperature of the turbine materials. The gap between rotating turbine blades and the stationary shroud provides an unintended flow path for hot gases. Gases that flow through the tip region cause pressure losses in the turbine section and high heat loads to the blade tip. This thesis studies the heat transfer on an innovative tip geometry intended to help reduce aerodynamic losses. The blade tip has a depression (shelf) on the tip surface along much of the pressure side of the blade and film-cooling holes along the depression. This research experimentally measured the effect of the shelf, coolant flow and tip gap on heat transfer on the blade tip. Stationary experiments were performed in a low speed wind tunnel on a linear cascade with two different tip gaps and multiple coolant flow rates through the film-cooling holes. Tests showed that baseline Nusselt numbers on the tip surface were reduced with the shelf tip compared with a flat tip. Measurements indicated that film-cooling was more effective with a small tip gap than with a large tip gap. Experimental and computational results demonstrated a lack of coolant spreading that was detrimental to regions between the film-cooling holes. While the coolant was effective on the blade tip, the leading and trailing edge regions were found to have high heat transfer coefficients with little available cooling. / Master of Science

The present study focuses on local heat transfer characteristics on the tip and near-tip regions of a turbine blade with a flat tip, tested under transonic conditions in a stationary, 2-D linear cascade consisting of seven blades, the three center blades having a variable tip clearance gap. The effects of tip clearance and exit Mach number on heat transfer distribution were investigated on the tip surface using a transient infrared thermography technique. In addition, thin film gages were used to study similar effects on the near-tip regions at 94% based on engine blade span of the pressure and suction sides. The experiments were conducted at the Virginia Tech transonic blow-down wind tunnel facility with a seven-blade linear cascade. Surface oil flow visualizations on the blade tip region were carried-out to shed some light on the leakage flow structure. Experiments were performed at three exit Mach numbers of 0.7, 0.85, and 1.05 for two different tip clearances of 0.9% and 1.8% based on engine blade span. The exit Mach numbers tested correspond to exit Reynolds numbers of 7.6 x 105, 9.0 x 105, and 1.1 x 106 based on blade true chord. The tests were performed with a freestream turbulence intensity of 12%. Results at 0.85 exit Mach showed that an increase in the tip gap clearance translates into a 12% increase in the heat transfer coefficients on the blade tip surface. Similarly, at 0.9% tip clearance, an increase in exit Mach number from 0.85 to 1.05 also led to a 24% increase in heat transfer on the tip. High heat transfer was obtained at the leading edge area of the blade tip, and an increase in the tip clearance gap and exit Mach number augmented this leading edge heat transfer. At 94% of engine blade span on the suction side near the tip, a peak in heat transfer was observed in all test cases at an s/C of 0.66 due to the onset of a downstream leakage vortex. At the design condition, this peak represents an increase of a factor of 2.5 from the immediate preceding s/C location. An increase in both the tip gap and exit Mach number resulted in an increase, followed by a decrease in the near-tip suction side heat transfer. On the near-tip pressure side, a slight increase in heat transfer was observed with increased tip gap and exit Mach number. In general, the suction side heat transfer is greater than the pressure side heat transfer as a result of the suction side leakage vortices. / Master of Science

Instances in which we cannot retrieve information immediately but know that the information might be retrieved later are subjective states that accompany retrieval failure. These are expressed in feeling-of-knowing (FOK) and Tip-of-the-tongue (TOT) experiences. In Experiment 1, participants with Parkinson's disease (PD) and older adult controls were given general questions and asked to report when they experienced a TOT state and to give related information about the missing word. The PD group experienced similar levels of TOTs but provided less correct peripheral information related to the target when in a TOT state. In Experiment 2, participants were given a Semantic (general knowledge questions) and an Episodic (word pairs) FOK task. PD patients failed to accurately predict their future memory performance (FOK) in response to both episodic and semantic cues. Results are interpreted in the context of recent frameworks of memory and metacognition.

A computer-based parametric study of the effect of reinforcement architectures on fracture response of aluminum compact-tension (CT) specimens was performed using the finite element code ABAQUS. A three-dimensional crack propagation procedure based on the crack tip opening angle (CTOA) was developed using Python. Eleven different reinforcement architectures consisting of rectangular and triangular cross-section reinforcements were evaluated. Reinforced specimens produced between 13 and 28 percent higher fracture load than achieved with the non-reinforced case. Reinforcements with blunt leading edges (rectangular reinforcements) exhibited superior performance relative to the triangular reinforcements with sharp leading edges. Relative to the rectangular reinforcements, the most important architectural feature was reinforcement thickness. At failure, the reinforcements carried between 58 and 85 percent of the load applied to the specimen, suggesting that there is considerable load transfer between the base material and the reinforcement. The amount of load transfer is linked to strains experienced by the reinforcement ahead of the crack tip. / Master of Science

The objective of this work is to examine the flow structure and heat transfer distribution of a squealer tip rotor blade with purge flow cooling and provide a comparison with a basic flat tip rotor blade without purge flow cooling, under transonic conditions and high inlet free stream turbulence intensity. The blade design was provided by Solar Turbines Inc., and consists of a double squealer around the pressure and suction sides, two purge flow blowing holes located downstream of the leading edge and mid-chord, four ribs in the mid-chord region and a trailing edge bleeder exiting on the pressure side. Blade cavity depth is 2.29 mm (0.09 in.) and the total blade turning angle is 107.5°. Tests were performed in a blow-down facility at a turbulence intensity of 12%, in a seven bladed 2-D linear cascade at transonic conditions. Experiments were conducted at isentropic exit Mach numbers of 0.85 and 1.05, corresponding to Reynolds numbers based on axial chord of 9.75x10^5 and 1.15x10^6, respectively, and tip clearance gaps of 1% and 2% of the scaled engine blade span. A blowing ratio of 1.0 was used in the squealer tip experiments. Detailed heat transfer coefficient and film cooling effectiveness distributions were obtained using an infrared thermography technique, while oil flow visualization was used to investigate the flow patterns in the blade tip region. With the addition of a squealer tip, leakage flow was found to decrease, as compared to a flat tip blade. With increasing tip clearance gap, the heat transfer coefficients within the cavity and along the squealer rim were found to decrease and increase, respectively. Film cooling effectiveness decreased with increasing tip clearance gap and was mainly observed within the squealer cavity. The maximum heat transfer coefficient was observed on the leading edge, however, comparatively large values were observed on the mid-chord ribs. The presence of the ribs, greatly affected the flow structure and heat transfer distributions within the cavity and downstream towards the trailing edge. / Master of Science

A three-dimensional unstructured incompressible RANS code has been developed using artificial compressibility and Spalart-Allmaras eddy viscosity model. A node-based finite volume method is used in which all flow variables are defined at the vertices of tetrahedrons in an unstructured grid. The inviscid fluxes are computed by using the Roe's flux difference splitting method, and higher order accuracy is attained by data reconstruction based on Taylor series expansion. Gauss theorem is used to formulate necessary gradients. For time integration, an implicit scheme based on linearized Euler backward method is used. A tetrahedral unstructured grid generation code has been also developed and applied to the tip clearance flow in a highly staggered cascade. Surface grids are first generated in the flow passage and blade tip by using several triangulation methods including Delaunay triangulation, advancing front method and advancing layer method. Then the whole computational domain including tip gap region is filled with prisms using the surface grids. Each prism is divided into three tetrahedrons. To accomplish this division in a consistent manner, connectivity pattern is assigned to each triangle in the surface grids. A new algorithm is devised to assign the connectivity pattern without reference to the particular method of triangulation. This technique offers great flexibility in surface grid generation. The code has been validated by comparisons with available computational and experimental results for several test cases: invisicd flow around NACA section, laminar and turbulent flow over a flat plate, turbulent flow through double-circular arc cascade and laminar flow through a square duct with 90° bend. For the laminar flat plate case, the velocity profile and skin friction coefficient are in excellent agreement with Blasius solution. For the turbulent flat plate case, velocity profiles are in full agreement with the law of the wall up to Reynolds number of 1.0E8, however, the skin friction coefficient is under-predicted by about 10% in comparison with empirical formula. Blade loading for the two-dimensional circular arc cascade is also compared with experiments. The results obtained with the experimental inflow angle (51.5° ) show some discrepancies at the trailing edge and severely under-predict the suction peak at the leading edge. These discrepancies are completely remedied if the inflow angle is increased to 53.5° . The code is also capable of predicting the secondary flow in the square duct with 90° bend, and the velocity profiles are in good agreement with measurements and published Navier-Stokes computations. Finally the code is applied to a linear cascade that has GE rotor B section with tip clearance and a high stagger angle of 56.9° . The overall structure of the tip clearance flow is well predicted. Loss of loading due to tip leakage flow and reloading due to tip leakage vortex are presented. On the end wall, separation line of the tip leakage vortex and reattachment line of passage vortex are identified. The location of the tip leakage vortex in the passage agrees very well with oil flow visualization. Separation bubble on the blade tip is also predicted. Mean streamwise velocity contours and cross sectional velocity vectors are compared with experimental results in the near wake, and good agreements are observed. It is concluded that Spalart-Allmaras turbulence model is adequate for this type of flow field except at locations where the tip leakage vortex of one blade interacts with the wake of a following blade. This situation may prevail for blades with longer span and/or in the far wake. Prediction of such an interaction presents a challenge to RANS computations. The effects of blade span on the flow structure have been also investigated. Two cascades with blades of aspect ratios of 0.5 and 1.0 are considered. By comparing pressure distributions on the blade, it is shown that the aspect ratio has strong effects on loading distribution on the blade although the tip gap height is very small (0.016 chord). Grid convergence study has been carried out with three different grids for pressure distributions and limiting streamlines on the end wall. / Ph. D.

Miniature pressure sensors which can endure harsh environments are a highly sought after goal in industrial, medical and research fields. Microelectromechanical systems (MEMS) are the current methods to fabricate such small sensors. However, they suffer from low sensitivity and poor mechanical properties. To fulfill the need for robust and reliable miniature pressure sensors that can operate under high temperatures, a novel type of optical fiber tip sensor only 125μm in diameter is presented in this thesis. The essential element is a piece of hollow fiber which connects the fiber end and a diaphragm to form a Fabry-Pérot cavity. The all-fused-silica structure fabricated directly on a fiber tip has little temperature dependence and can function very well with high resolution and accuracy at temperatures up to 600 °C. In addition to its miniature size, its advantages include superior mechanical properties, biocompatibility, immunity to electromagnetic interference, disposability and cost-effective fabrication. The principle of operation, design analysis, fabrication implementation and performance evaluation of the sensor are discussed in detail in the following chapters. / Master of Science

Este trabalho teve como objetivo observar, analisar e discutir como ocorre a busca por sinais-alvo, em indivíduos surdos, fluentes na Língua Brasileira de Sinais (Libras); verificar se ocorre, nesses indivíduos o fenômeno ponta dos dedos (TOF); e descrever os aspectos fonético-fonológicos na ocorrência do fenômeno. O TOF corresponde ao fenômeno ponta da língua (TOT) nas línguas orais. Esse fenômeno ocorre quando há o esquecimento momentâneo de palavras conhecidas e o sentimento de que essa palavra está prestes a ser recuperada. Tal fenômeno oferece pistas sobre o processamento da linguagem e a recuperação lexical. Poucos trabalhos foram realizados sobre este fenômeno nas línguas de sinais (THOMPSON; EMMOREY; GOLLAN, 2005) e essa investigação é importante, pois, por ser uma língua de modalidade distinta (visual-espacial), possui processos fonológicos particulares. Nesse sentido, foi elaborado um teste para eliciar o fenômeno em 34 adultos surdos, que relataram utilizar a Libras como principal meio de comunicação. O teste consistia na realização do sinal referente a personalidades famosas e a cidades no mundo. Foram exibidas imagens e o participante deveria dizer se sabia ou não o sinal referente à pessoa ou à cidade, ou se estava experienciando o TOF. Neste último caso, o participante deveria sinalizar o que lembrasse do sinal- alvo. Foram realizados 69 estímulos por participantes, somando um total de 2346 estímulos e, como resultado obtivemos a ocorrência de 20 TOFs (0,9% dos estímulos). Em todos os casos de TOF foi recuperado ao menos um dos parâmetros fonético-fonológicos (quais sejam, configuração de mão, localização/ espaço, orientação, movimento, número de mãos). Dos parâmetros fonético-fonológicos recuperados, a configuração de mão foi recuperada em 65% dos casos (13 vezes); a localização em 70% (14 vezes); o espaço em 85% (17 vezes); o movimento em 35% (7 vezes); a orientação em 50% (10 vezes); e o número de mãos em 90% dos casos (18 vezes). Corroboramos a conclusão de Thompson, Emmorey e Gollan (2005) de que o movimento é o parâmetro menos recuperado no momento do TOF. Esse fato pode indicar que os parâmetros localização, configuração de mão e orientação (mais recuperados no momento do TOF) constituem o onset da estrutura silábica do sinal, isto é, o segmento inicial do sinal. Além disso, a ocorrência do fenômeno ponta dos dedos na Libras ajuda a confirmar separação, no processamento da recuperação lexical em codificação semântica e codificação fonológica estabelecidas em modelos de recuperação de línguas orais (DELL, 1986; GARRETT, 1988; LEVELT, 1989). / The aim of this research is to analyze and discuss how the search for target signs occurs in the lexical retrieval in deaf people using Brazilian Sign Language (Libras); to verify if the \"tip of the fingers\" (TOF) phenomenon occurs; and describe the phonological aspects in the occurrence of the phenomenon. The TOF phenomenon mirrors the \"tip of the tongue\" phenomenon in oral languages. This phenomenon occurs when there is momentary forgetfulness of known words and the feeling that this word is about to be recovered. This phenomenon offers clues about language processing and lexical retrieval. Few studies have been carried out on this phenomenon in sign languages (THOMPSON; EMMOREY; GOLLAN, 2005) and this research is important because sign language has a different modality and therefore it has particular phonological processes. In this sense, a test was prepared to elicit the phenomenon in 34 deaf adults, who reported using Libras as the main means of communication. The test consisted of the signing regarding proper names of famous personalities and cities in the world. Images were displayed and the participant should say whether or not he knew the sign for the person or city, or whether he was experiencing TOF. In the latter case, the participant should sign what he remembered of the target signal. A total of 69 stimuli were performed per participant, totaling 2346 stimuli and, as a result, we obtained the occurrence of 20 TOFs (0.9% of the stimuli). In all TOF cases, at least one of the phonological parameters (ie, hand configuration, location / space, orientation, movement, number of hands) was retrieved. Of those, the hand configuration was recovered in 65% of the cases (13 times); the location in 70% (14 times); space 85% (17 times); movement in 35% (7 times); orientation by 50% (10 times); and the number of hands in 90% of the cases (18 times). We corroborate the conclusion of Thompson, Emmorey and Gollan (2005) that movement is the least recovered parameter at the time of TOF. This fact may indicate that the parameters localization, hand configuration and orientation (more retrieved while in TOF state) constitute the onset of the syllabic structure of the sign. In addition, the occurrence of the \"tip of the fingers\" phenomenon in Libras helps to confirm separation, in the processing of lexical retrieval in semantic encoding and phonological encoding established in lexical retrieval models of oral language (GARRETT, 1988; LEVELT, 1989).