Recent design trends in steam turbines strive for high aerodynamic loading and high aspect ratio to meet the demand of higher efficiency. These design trends together with the low structural frequency in last stage steam turbines increase the susceptibility of the turbine blades to flutter. Flutter is the self-excited and self-sustained aeroelastic instability phenomenon, which can result in rapid growth of blade vibration amplitude and eventually blade failure in a short period of time unless adequately damped. To prevent the occurrences of flutter before the operation of new steam turbines, a compromise between aeroelastic stability and stage efficiency has to be made in the steam turbine design process. Due to the high uncertainty in present flutter prediction methods, engineers use large safety margins in predicting flutter which can rule out designs with higher efficiency. The ability to predict flutter more accurately will allow engineers to push the design envelope with greater confidence and possibly create more efficient steam turbines. The present work aims to investigate the influence of tip clearance flow on the prediction of steam turbine flutter characteristics. Tip clearance flow effect is one of the critical factors in flutter analysis for the majority of aerodynamic work is done near the blade tip. Analysis of the impact of tip clearance flow on steam turbine flutter characteristics is therefore needed to formulate a more accurate aeroelastic stability prediction method in the design phase.Besides the tip leakage vortex, the induced vortices in the tip clearance flow can also influence blade flutter characteristics. However, the spatial distribution of the induced vortices cannot be resolved by URANS method for the limitation of turbulence models. The Detached-Eddy Simulation (DES) calculation is thus applied on a realistic-scale last stage steam turbine model to analyze the structure of induced vortices in the tip region. The influence of the tip leakage vortex and the induced vortices on flutter prediction are analyzed separately. The KTH Steam Turbine Flutter Test Case is used in the flutter analysis as a typical realistic-scale last stage steam turbine model. The energy method based on 3D unsteady CFD calculation is applied in the flutter analysis. Two CFD solvers, an in-house code LUFT and a commercial software ANSYS CFX, are used in the flutter analysis as verification of each other. The influence of tip leakage vortex on the steam turbine flutter prediction is analyzed by comparing the aeroelastic stability of two models: one with the tip gap and the other without the tip gap. Comparison between the flutter characteristics predicted by URANS and DES approaches is analyzed to investigate the influence of the induced vortices on blade flutter characteristics. The multiple induced vortices and their relative rotation around the tip leakage vortex in the KTH Steam Turbine Flutter Test Case are resolved by DES but not by URANS simulations. Both tip leakage vortex and induced vortices have an influence on blade loading on the rear half of the suction side near the blade tip. The flutter analysis results suggest that the tip clearance flow has a significant influence on blade aerodynamic damping at the least stable interblade phase angle (IBPA), while its influence on the overall shape of the damping curve is minor. At the least stable IBPA, the tip leakage vortex shows a stabilization effect on rotor aeroelastic stabilities while the induced vortices show a destabilization effect on it. Meanwhile, a non-linear unsteady flow behavior is observed due to the streamwise motion of induced vortices during blade oscillation, which phenomenon is only resolved in DES results.

The subthalamic nucleus (STN) is a key structure for motor, limbic and associative function. Parkinson's disease (PD) and Obsessive compulsive disorder (OCD) have been connected to abnormal firing activity of STN neurons. Subthalamotomy and deep brain stimulation (DBS) of the STN have been shown to be effective treatment methods for previous suggested diagnosis, however, the mechanism behind the treatment and the reason for adverse side-effects remains unsolved. The aim of this study was to establish if it is possible to distinguish specific gene expressions in structures of transgenic mouse brains as well as gaining more knowledge about the medial part of STN, which is hypothesized to be the limbic part of the structure. Here, immunofluorescence and PCR was performed on Cre-driven transgenic mice followed by histological analysis in order to identify the distribution of tachykinin 1 (Tac1) and paired-like homeodomain 2 (Pitx2) in these transgenic mice brains. The results demonstrate that STN and pSTN were positive structures in Pitx2-CreSunGFP and Tac1-CreSunGFP mice. Tac1-CreSunGFP mice further contained GFP positive cells in striatum, nucleus accumbens, amygdala, thalamus, hypothalamus, submedial nucleus of thalamus and the septal area, proposing the gene expression of Tac1 to be present in several limbic structures. Today, we lack knowledge of the internal organization of the STN, and solving the structural-functional organization of the STN would be helpful to distinguish distinct roles of STN neurons and develop effective STN-DBS-targeting treatment without side-effects.

The unsteady behavior of a tip leakage flow downstream of a simulated axial compressor rotor has been studied. The Virginia Tech low speed linear cascade wind tunnel was adapted to model the unsteady tip leakage flow produced by a rotor operating in the vortical wakes of a set of stator vanes. The cascade, consisting of 8 GE rotor B blades, has adjustable tip gap, inlet angle of 65.1 degrees, turning angle of 11.8 degrees and solidity of 1.076. The cascade Reynolds number, based on blade chord, was 393,000. A moving end wall was used to simulate the relative motion between rotor and casing, and vortex generators attached to the moving end wall were used to produce an idealized periodic unsteady vortical inflow similar to that shed by the junction of a row of inlet guide vanes. Measurements of the vortical inflow to the cascade produced by the generators and of the mean blade loading at the mid span are presented. The periodic and aperiodic behavior of the tip leakage flow downstream of the cascade, produced by this vortical disturbance, is also presented using phase and time averaged 3-component turbulence and pressure fluctuation measurements. These measurements are made for tip gap from 0.83% to 3.3% chord and streamwise locations from 0.772% to 1.117% blade spacing axially downstream of the cascade. The phase averaged inflow measurements reveal that the inflow produced by the vortex generators consists of a pair asymmetric counter-rotating vortices embedded in a thin (4.6% chord) endwall boundary layer. The vortices extend some 7.4% chord from the end wall. Their strength is about two orders smaller than the typical circulation of the tip leakage vortices produced by the cascade. Phase averaged single point three component hot-wire measurements downstream of the cascade reveal that the vortical inflow is, however, capable of producing significant large scale fluctuations in the size, strength, structure and position of the tip leakage vortex. These effects increase in magnitude with increase of tip gap. For small tip gaps these effects appear to be due to simple superposition between the inflow vortices and the tip leakage vortex. However for larger tip gaps these effects appear primarily a consequence of the inflow vortices interfering with the shedding of circulation from the blade tip. The fact that the circulation fluctuation is consistent with the inviscid unsteady loading prediction suggests that the inviscid response may be a major mechanism for generating the tip leakage unsteadiness. Although there is large periodic fluctuation in the tip leakage flow disturbed by the inflow, there is a larger aperiodic component. Two point correlation measurements and linear stochastic estimation are used to reveal the structure of this aperiodic part for a tip gap of 3.3% chord. The aperiodic fluctuation, containing most of the turbulence energy, is found appearing to be organized structures in large scale, and making the estimated instantaneous velocity field significantly different from the phase averaged periodic velocity field. Phase averaged pressure fluctuation measurements made using a microphone in the tip leakage vortex downstream of the cascade reveal that there are significant periodic fluctuating pressure waves and intense mean square fluctuation of the aperiodic fluctuating pressure. They are consistent with the measured periodic flow and aperiodic flow field respectively. These microphone measurements are validated using fluctuating pressure gradient estimates determined from the hot-wire measurements. / Ph. D.

The interaction between rotor blade tip leakage vortex and inflow disturbances, such as encountered in shrouded marine propulsors, was simulated in the Virginia Tech Linear Cascade Wind Tunnel equipped with a moving endwall system. Upstream of the blade row, idealized periodic inflow unsteadiness was generated using vortex generator pairs attached to the endwall at the same spacing as the blade spacing. At three tip gap settings, 1.7%c, 3.3%c and 5.7%c, the flow near the lower endwall of the center blade passage was investigated through three-component mean velocity and turbulence distributions measured by four-sensor hotwires. Besides time-averaged data, the measurements were processed for phase-locked analysis, with respect to pitchwise locations of the vortex generators relative to the blade passage. Moreover, surface pressure distributions at the blade tip were acquired at eight tip gaps from 0.87%c to 12.9%c. Measurements of pressure-velocity correlation were also performed with wall motion but without inflow disturbances. Achieved in this study is an understanding of the characteristics and structures of the tip leakage vortex at its initial formation. The mechanism of the tip leakage vortex formation seems to be independent of the tip gap setting. The tip leakage vortex consists of a vortical structure and a region of low streamwise-momentum fluid next to the endwall. The vortical structure is initially attached to the blade tip that creates it. This structure picks up circulation shed from that blade tip, as well as those from the endwall boundary layer, and becomes stronger with downstream distance. Partially induced by the mirror images in the endwall, the vortical structure starts to move across the passage resulting in a reduction in its rotational strength as the cross sectional area of the vortex increases but little circulation is added. The larger the tip gap, the longer the vortical structure stays attached to the blade tip, and the stronger the structure when it reaches downstream of the passage. Phased-averaged data show that the inflow disturbances cause small-scale responses and large-scale responses upstream and downstream of the vortex shedding location, respectively. This difference in scale is possibly dictated by a variation in the shedding location since the amount of circulation in the vortex is dependent on this location. The inflow disturbances possibly cause a variation in the shedding location by manipulating the separation of the tip leakage flow from the endwall and consequently the flow's roll-up process. Even though this manipulation only perturbs the leakage flow in a small scale, the shedding mechanism of the tip leakage vortex amplifies the outcome. / Ph. D.

Turbine airfoils are exposed to the hottest temperatures in the gas turbine with temperatures typically exceeding the melting point of the blade material. Cooling methods investigated in this computational study included parasitic cooling flow losses, which are inherent to engines, and microcircuit channels. Parasitic losses included dirt purge holes, located along the blade tip, and platform leakage flow, which result from gaps between various turbine components. Microcircuits are a novel cooling technique involving small air passages placed near the airfoil surface to enhance internal cooling. This study evaluated the benefit of external film-cooling flow exhausted from strategically placed microcircuits. Along the blade tip, predictions showed mid-chord cooling was independent of the blowing from microcircuit exits. The formation of a pressure side vortex was found to develop for most microcircuit film-cooling cases. Significant leading edge cooling was obtained from coolant exiting from dirt purge holes with a small tip gap while little cooling was seen with a large tip gap. Along the blade platform, the migration of coolant from the front leakage was shown to cool a considerable part of the platform. Several hot spots were predicted along the platform, which were circumvented through the placement of microcircuit channels. Ingestion of hot mainstream gas was predicted along the aft portion of the gutter and agreed with distress exhibited by actual gas turbine engines. / Master of Science

There has been an increased interest among the tobacco industry in the production of tip leaves in flue-cured tobacco. Different harvest treatments of flue-cured tobacco were compared across six cultivars and two topping heights with the objective of identifying tip grade tobacco. Agronomic and cured leaf chemistry data were collected. Cultivar had significant influences on yield, average price, grade index, and value in three growing seasons. NC 71 and RG H51 were the highest yielding cultivars, with grade indices among the highest as well. Increasing topping height increased tobacco yield in two of three years. As topping height increased there was a significant increase in the percentage of tobacco receiving a tip grade. The four harvest treatments focused on the ten uppermost leaves of the plant. Harvest treatments that allowed proper separation of stalk positions (5&5L and 7&3L treatments) resulted in increased yields and tip grades. Harvest treatments that separate upper stalk position tobacco resulted in a higher percentage of tip grades from a tobacco company grader. Chemical analysis identified differences between stalk positions at the top of the plant. In order for cigarette manufacturers to properly blend the tobacco used to make American blend cigarettes, this separation of stalk positions is important. Harvest treatments that combined stalk positions resulted in the loss of these chemical differences. By topping flue-cured tobacco four to five leaves higher than current extension recommendations and separating stalk positions correctly, tobacco growers can meet the crop throw requirements of tobacco marketing contracts. / Master of Science

The primary purpose of this thesis is to quantify the effects of RANS turbulence modeling on the resolution of free shear vortical flows. The simulation of aerodynamic wing-tip vortices is used as a test bed. The primary configuration is flow over an isolated finite wing with aspect ratio, , and Reynolds number, . Tip-vortex velocity profiles, vortex core and wake turbulence levels, and Reynolds stresses are compared with wind tunnel measurements. Three turbulence models for RANS closure are tested: the Lumley, Reece, and Rodi full Reynolds stress transport model and the Sparlart-Allmaras model with and without a proposed modification. The main finding is that simulations with the full Reynolds stress transport model show remarkable mean flow agreement in the vortex and wake due to the proper prediction of a laminar vortex core. Simulations with the Spalart-Allmaras model did not indicate a laminar core and predicted over-diffusion of the tip-vortex. Secondary investigations in this work include the study of wall boundary layer treatment and simulating the wake-age of an isolated rotorcraft in hover using a steady-state RANS solver. By comparing skin friction plots over the NACA 0012 airfoil, it is shown that wall functions are most effective in the trailing edge half of the airfoil, while high velocity gradient and curvature of the leading edge make them more vulnerable to discrepancies. The rotorcraft simulation uses the modified Spalart-Allmaras turbulence model and shows proper, qualitative, resolution of the interaction between the vortex sheet and the tip vortex. / Master of Science

The Nantucket pine tip moth, Rhyacionis frustrana (Comstock) Is a common pest of young pines. In the eastern United States all species of yellow pines are attacked to some degree except longleaf pine, Pinus palustrla Mill. (Yates 1960). Chemical control of the tip moth has been demonstrated to be effective, but It generally has been considered to be too expensive since the evidence was only Inconclusive as to any permanent additional height growth of pines resulting from complete control. There has been considerable speculation about silvicultural control and a number of methods have been suggested by various workers. Many of these methods, however, have not been backed by quantitative data. Some of the suggested silvicultural controls are mixing susceptible species with resistant species, starting. trees under an overstory, using close spacing, and starting trees In brush. To date, there have been no detailed investigations of silvicultural control for the tip moth. This study was designed to determine if stands of loblolly pine, Pinus taeda L., growing under various conditions show any differences in rate of attack by the tip moth that might, In the future, be a basis for silvicultural or integrated control. / Master of Science

Habitat alteration (i.e. degradation, fragmentation, and destruction) is the primary driver of amphibian decline and extinction. Despite their ecological importance and threatened status, very little long-term research has been conducted on how methods of forest management impact salamanders. In this research, I examine how experimental silviculture impacts plethodontid salamander relative abundance and count, and I compare three different body condition indices. Chapter 1 focuses on plethodontid salamander relative abundance 30 years after experimental treatments (including clearcut and shelterwood harvests, understory herbicide, uneven-aged management, and an untreated control) were first applied. I found that plethodontid salamander populations in all silvicultural treatments without stand re-entry have reached pre-harvest relative abundance levels. Chapter 2 describes how artificial tip-up mounds that could be used to mimic old-growth forest characteristics impact plethodontid salamander count. Salamander count significantly declined in treatment units with artificial tip-up mounds but this could be an artifact of the heavy disturbance required for installation. Chapter 3 compares three different body condition indices for plethodontid salamanders. I found that bioelectrical impedance analysis (BIA) is likely not suitable for use with plethodontid salamanders and mass divided by snout-to-vent-length is likely a superior estimate to tail width divided by snout-to-vent-length. These findings further our understanding of how different forest management practices affect salamander populations and provide guidance for evaluating body condition. / Master of Science / Forest understory salamanders play an important role in energy transfer and their position in leaf litter food webs affects multiple ecosystem functions. Despite their ecological importance, very little long-term research has been conducted on how habitat change impacts salamanders. This research investigates how different forest management techniques influence forest-dwelling salamanders and compares three different ways to evaluate salamander health. Chapter 1 focuses on the salamanders 30 years post-harvest. I found that salamander populations in all silvicultural treatments except one had recovered. Chapter 2 described how tipping over trees to mimic old-growth forest characteristics impacts the number of forest-dwelling salamanders. There were significantly fewer salamanders in treatment units after the disturbance created by installing artificial tip-up mounds. Chapter 3 compares three different ways to evaluate forest-dwelling salamander health. I found that bioelectrical impedance analysis (BIA)is likely not suitable for forest-dwelling salamanders, and weight divided by body length is likely a superior estimate to tail width divided by body length. These findings together further our understanding of how different forest management practices affect salamander populations and provide guidance for evaluating body condition.

The tips of unshrouded, high-pressure turbine blades are prone to significantly high heat loads. The gap between the tip and over-tip casing is the root cause of undesirable over-tip leakage flow that is directly responsible for high thermal material degradation and is a major source of aerodynamic loss within a turbine. Both must be minimised for the safe working and improved performance of future gas-turbines. A joint experimental and numerical study is presented to understand and characterise the heat transfer and aerodynamics of unshrouded blade tips. The investigation is undertaken with the use of a squealer or cavity tip design, known for offering the best overall compromise between the tip aerodynamics, heat transfer and mechanical stress. Since there is a lack of understanding of these tips at engine-realistic conditions, the present study comprises of a detailed analysis using a high-speed linear cascade and computational simulations. The aero-thermal performance is studied to provide a better insight into the behaviour of squealer tips, the effects of casing movement and tip cooling. The linear cascade environment has proved beneficial for its offering of spatially-resolved data maps and its ability to validate computational results. Due to the unknown tip gap height within an entire engine cycle, the effects of gap height are assessed. The squealer's aero-thermal performance has been shown to be linked with the gap height, and qualitative different trends in heat transfer are established between low-speed and high-speed tip flow regimes. To the author's knowledge, the present work is the first of its kind, providing comprehensive aero-thermal experimental research and a dataset for a squealer tip at engine-representative transonic conditions. It is also unique in terms of conducting direct and systematic validations of a major industrial computational fluid dynamics method for aero-thermal performance prediction of squealer tips at enginerepresentative transonic conditions. Finally, after recognising the highest heat loads are found on the squealer rims, a novel shaped squealer tip has been investigated to help improve the thermal performance of the squealer with a goal to improve its durability. It has been discovered that a seven percent reduction in tip temperature can be achieved through incorporating a shaped squealer and maximising the internal cooling performance.