Gas turbine companies are always focused on reducing capital costs and increasing overall efficiency. There are numerous advantages in reducing the number of airfoils per stage in the turbine section. While increased airfoil loading offers great advantages like low cost and weight, they also result in increased aerodynamic losses and associated issues. The strength of secondary flows is influenced by the upstream boundary layer thickness as well as the overall flow turning angle through the blade row. Secondary flows result in stagnation pressure loss which accounts for a considerable portion of the total stagnation pressure loss occurring in a turbine passage. A turbine designer strives to minimize these aerodynamic losses through design changes and geometrical effects. Performance of airfoils with varying loading levels and turning angles at transonic flow conditions are investigated in this study. The pressure difference between the pressure side and suction side of an airfoil gives an indication of the loading level of that airfoil. Secondary loss generation and the 3D flow near the endwalls of turbine blades are studied in detail. Detailed aerodynamic loss measurements, both in the pitchwise as well as spanwise directions, are conducted at 0.1 axial chord and 1.0 axial chord locations downstream of the trailing edge. Static pressure measurements on the airfoil surface and endwall pressure measurements were carried out in addition to downstream loss measurements. The application of endwall contouring to reduce secondary losses is investigated to try and understand when contouring can be beneficial. A detailed study was conducted on the effectiveness of endwall contouring on two different blades with varying airfoil spacing. Heat transfer experiments on the endwall were also conducted to determine the effect of endwall contouring on surface heat transfer distributions. Heat transfer behavior has significant effect on the cooling flow needs and associated aerodynamic problems of coolant-mainstream mixing. One of the primary objectives of this study is to provide data under transonic conditions that can be used to confirm/refine loss predictions for the effect of various Mach numbers and gas turning. The cascade exit Mach numbers were varied within a range from 0.6 to 1.1. A published experimental study on the effect of end wall contouring on such high turning blades at high exit Mach numbers is not available in open literature. Hence, the need to understand the parametric effects of endwall contouring on aerodynamic and heat transfer performance under these conditions. / Ph. D.

Airfoil endwall contouring has been widely studied during the past two decades for the reduction of secondary losses in turbine passages. Although many endwall contouring methods have been suggested by researchers, an analytical tool based on the passage design parameters is still not available for designers. Hence, the best endwall contour shape is usually decided through an optimization study. Moreover, a general guideline for the endwall shape variation can be extrapolated from the existing literature. It has not been validated whether the optimum endwall shape for one passage can be fitted to other similar passage geometry to achieve, least of all a non-optimum but a definite, reduction in losses. Most published studies were conducted at low exit Mach numbers and only recently some studies on the effect of endwall contouring on aerodynamics performance of a turbine passage at high exit Mach numbers have been published. There is, however, no study available in the open literature for a very high turning blade with a transonic design exit Mach number and the effect of endwall contouring on the heat transfer performance of a turbine passage. During the present study, a robust, aerodynamic performance based numerical optimization methodology for turbine endwall contouring has been developed. The methodology is also adaptable to a range of geometry optimization problems in turbomachinery. It is also possible to use the same methodology for multi-objective aero-thermal optimization. The methodology was applied to a high turning transonic turbine blade passage to achieve a geometry based on minimum total pressure loss criterion. The geometry was then compared with two other endwall geometries. The first geometry is based on minimum secondary kinetic energy value instead of minimum total pressure loss criterion. The second geometry is based on a curve combination based geometry generation method found in the literature. A normalized contoured surface topology was extracted from a previous study that has similar blade design parameters. This surface was then fitted to the turbine passage under study in order to investigate the effect of such trend based surface fitting. Aerodynamic response of these geometries has been compared in detail with the baseline case without any endwall contouring. A new non-contoured baseline design and two contoured endwall designs were provided by Siemens Energy, Inc. The pitch length for these designs is about 25% higher than the turbine passage used for the endwall optimization study. The aerodynamic performance of these endwalls was studied through numerical simulations. Heat transfer performance of these endwall geometries was experimentally investigated in the transonic turbine cascade facility at Virginia Tech. One of the contoured geometries was based on optimum aerodynamic loss reduction criterion while the other was based on optimum heat transfer performance criterion. All the three geometries were experimentally tested at design and off-design Mach number conditions. The study revealed that endwall contouring results in significant performance benefit from the heat transfer performance point of view. / Ph. D.

Model fan blades designed to implement the wake management technique of trailing-edge blowing were tested in a linear cascade configuration. Measurements were made on two sets of blowing blades installed in the Virginia Tech low-speed linear cascade wind tunnel. The simple blowing blades were identical to the baseline GE Rotor B blades, aside from a slight difference in trailing-edge thickness, a set of internal flow passages, and a blowing slot just upstream of the trailing-edge on the suction side of the blade. The Kuethe vane blades were also slightly thicker at the trailing-edge, and had a set of nine evenly spaced vortex generators upstream of the blowing slot on the suction side. The cascade tunnel accommodates eight blades with adjustable tip-gap heights, although only the center four blades were replaced by blowing blades in this study. The tunnel has an inlet angle of 65.1â a, a stagger angle of 56.9â a and a flow turning angle of 11.8â a. The tip-gap was set to 0.004125c and the freestream velocity of 24.7m/s led to a Reynolds number based on the chord of 385,000. Blowing slot uniformity measurements made with a single hot-wire immediately behind the trailing-edge revealed that the blowing becomes more spanwise uniform as blowing rate is increased. The same occurs with the Kuethe vane blades, despite a spanwise serrated pattern that appears as a result of the upstream vortex generators. Cross-sections made perpendicular to the blade span gave preliminary evidence that the simple blowing wake deficit increases from the passive suction case at a blowing rate of 1.4% and becomes overblown by 2.6%. The Kuethe vane wake deficit does not increase at low blowing rates. Both sets of blowing blades indicated a slight angling of the wake towards the pressure side with blowing. Pitot-static full cross-sections of the simple blowing blades at x/ca = 0.839 and 1.877 verified the increase in wake depth and width at 1.4% as compared to the passive suction and non-blowing baseline cases, and the wake overblowing that occurs as blowing rate is increased to approximately 2.6%. The Kuethe vane blades only achieve partial wake cancellation at the maximum tested rate of 2.6% for these measurements. The results of the baseline study of Geiger (2005) are used for comparison with the mid-span velocity profiles made at four downstream locations. The velocity profiles clearly confirm the results of the normal-to-span and full cross-sections, while also revealing a decrease from the baseline of at least 25% in most of the maximum Reynolds normal stresses and turbulent kinetic energies at all rates between 1.4% and 2.7% for both sets of blowing blades. Spectral measurements of the simple blowing blades show clear reductions of the energy in the wake for all blowing rates over the majority of the range of normalized frequencies, while the Kuethe vane blades show reductions at all rates and all frequencies. By performing Fourier decompositions, the tone noise benefits over the non-blowing baseline blades are directly comparable in decibels. The optimum blowing rate for the simple blowing blades is clearly 2.5%, since this rate shows the most potential tone noise reduction. The Kuethe vane blades suggest decreases in tone noise over all of the tested blowing rates. / Master of Science

This work presents a comparison of thin film gauge (TFG) and infrared (IR) thermography measurement techniques to simultaneously determine heat transfer coefficient and film cooling effectiveness. The first comparison was with an uncooled vane where heat transfer coefficient was measured at Mex=0.77 and Tu=16%. Relatively good agreement was found between the results of the two methods and the effect of recovery temperature and data reduction time was analyzed. Improvements were made to the experimental set up for the next comparison, a showerhead film cooled vane. This geometry was tested at BR=0, 2.0, Mex=0.76 and Tu=16%. The TFG and IR results did not compare well for heat transfer coefficient or film cooling effectiveness. The effects of measured and calculated recovery temperature were analyzed as well as the respective data reduction methods, though the analysis could not account for the effectiveness trend seen on the suction surface. Finally, a vane with showerhead and shaped film cooling holes were presented at BR=0, 1.7, 2.0, 2.8, Mex=0.85, and Tu=13% to assess a new film cooling geometry measured with the IR technique. Similarities on the suction surface trend between the different film cooled geometries tested with IR indicate a flaw in the experiment that will require further analysis, changes and testing to complete the comparison with TFG. / Master of Science

In the drive to increase cycle efficiency, gas turbine designers have increased turbine inlet temperatures well beyond the metallurgical limits of engine components. In order to prevent failure and meet life requirements, turbine components must be cooled well below these hot gas temperatures. Film cooling is a widely employed cooling technique whereby air is extracted from the compressor and ejected through holes on the surfaces of hot gas path components. The cool air forms a protective film around the surface of the part. Accurate numerical prediction of film cooling performance is extremely difficult so experiments are required to validate designs and CFD tools. In this study, a first stage turbine vane with five rows of showerhead cooling was instrumented with platinum thin-film gauges to experimentally characterize film cooling performance. The vane was tested in a transonic vane cascade in Virginia Tech's heated, blow-down wind tunnel. Two freestream exit Mach numbers of 0.76 and 1.0—corresponding to exit Reynolds numbers based on vane chord of 1.1x106 and 1.5x106, respectively—were tested at an inlet freestream turbulence intensity of two percent and an integral length scale normalized by vane pitch of 0.05. The showerhead cooling scheme was tested at blowing ratios of 0 (no cooling), 1.5, and 2.0 and a density ratio of 1.35. Midspan Nusselt number and film cooling effectiveness distributions over the surface of the vane are presented. Film cooling was found to augment heat transfer and reduce adiabatic wall temperature downstream of injection. In general, an increase in blowing ratio was shown to increase augmentation and film cooling effectiveness. Increasing Reynolds number was shown to increase heat transfer and reduce effectiveness. Finally, comparing low turbulence measurements (Tu = 2%) to measurements performed at high freestream turbulence (Tu = 16%) by Nasir et al. [13] showed that large-scale high freestream turbulence can reduce heat transfer coefficient downstream of injection. / Master of Science

This paper experimentally investigates the effect of high freestream turbulence intensity, turbulence length scale, and exit Reynolds number on the surface heat transfer distribution of a turbine blade at realistic engine Mach numbers. Passive turbulence grids were used to generate freestream turbulence levels of 2%, 12%, and 14% at the cascade inlet. The turbulence grids produced length scales normalized by the blade pitch of 0.02, 0.26, and 0.41, respectively. Surface heat transfer measurements were made at the midspan of the blade using thin film gauges. Experiments were performed at exit Mach numbers of 0.55, 0.78 and 1.03 which represent flow conditions below, near, and above nominal conditions. The exit Mach numbers tested correspond to exit Reynolds numbers of 6 x 105, 8 x 105, and 11 x 105, based upon true chord. The experimental results showed that the high freestream turbulence augmented the heat transfer on both the pressure and suction sides of the blade as compared to the low freestream turbulence case. At nominal conditions, exit Mach 0.78, average heat transfer augmentations of 23% and 35% were observed on the pressure side and suction side of the blade, respectively. / Master of Science

The design of last stage low pressure steam (LP) turbines has become increasingly complicated as turbine manufacturers have pushed for larger and more efficient turbines. The tip sections of these LP turbines encounter condensing wet steam at high velocities resulting in increased losses. These losses are difficult to predict with computational fluid dynamic models. To study these losses and improve the design of LP turbines a study was commissioned to determine the feasibility and cost of a steam cascade facility for measuring low pressure turbine blade tip section aerodynamic and thermodynamic performance. This study focused on two objectives: 1) design a steam production facility capable of simulating actual LP turbine operating conditions, and 2) design an instrumentation system to measure blade performance in wet steam. The steam production facility was designed to allow the test section size to be selected later. A computer code was developed to model the facility cycle and provide equipment requirements. Equipment to meet these requirements, vendors to provide it, and costs were found for a range of test section sizes. A method to control the test section conditions was also developed. To design the instrumentation system two methods of measuring blade losses through entropy generation were proposed. The first method uses existing total pressure probe techniques. The second method uses advanced particle imaging velocimetry techniques possibly for the first time in wet steam. A new method is then proposed to modify the two techniques to take measurements at non-equilibrium states. Finally accuracy issues are discussed and the challenges associated with achieving periodic flow in this facility are investigated. / Master of Science

Nous avons développé un récepteur hétérodyne terahertz (THz) compact et ultra-sensible à base de laser à cascade quantique (QCL) comme oscillateur local et de bolomètre à électron chaud (HEB) comme mélangeur. Le récepteur est basé sur un nouveau concept pour le couplage quasi-optique entre l'oscillateur local et le mélangeur ce qui a permis de ne pas utiliser de lame semi-réfléchissante pour la superposition du signal provenant du QCL et du signal à détecter. Le mélangeur utilisé est un HEB en nitrure de niobium avec une antenne planaire formée d’une double hélice log-spiral. Le HEB est monté sur la partie plane d’une lentille convexe en silicium. L’oscillateur local est un QCL que nous avons développé avec un système de contre-réaction répartie du troisième ordre avec une faible dissipation thermique, un faisceau peu divergent et un fonctionnement mono-mode à la fréquence cible de 2.7 THz. Le couplage entre l’oscillateur local et le mélangeur HEB a également été amélioré en couplant le QCL avec une fibre creuse en diélectrique ce qui a permis d’améliorer la directivité du faisceau laser à 55 dBi. Grâce aux précédents résultats, nous avons obtenu un récepteur THz hétérodyne compact qui présente une sensibilité proche de l’état de l’art à 2.7 THz. / We demonstrate an ultra-compact Terahertz (THz) heterodyne detec- tion system based on a quantum cas- cade laser (QCL) as local oscillator and a hot electron bolometer (HEB) for the mixing. It relies on a new opti- cal coupling scheme where the local oscillator signal is coupled through the air side of the planar HEB an- tenna, while the signal to be de- tected is coupled to the HEB through the lens. This technique allows us to suppress the beam splitter usu- ally employed for heterodyne mea- surements. The mixer is a Niobium Nitride HEB with a log-spiral planar antenna on silicon and mounted on the back of a plano-convex silicon lens. We have developed a low power consumption and low beam di- vergence 3rd-order distributed feed- back laser with single mode emis- sion at the target frequency of 2.7 THz to be used as local oscillator for the heterodyne receiver. The cou- pling between the QC laser and the the HEB has been further optimized, using a dielectric hollow waveguide that reliably increases the laser beam directivity up to 55 dBi. Upon the high beam quality, sufficient output power in a single mode at the tar- geted frequency and low power dissi- pation of our local oscillator, we have build an ultra compact THz hetero- dyne receiver with sensitivity close to the state of the art at 2.7 THz.

Monitoring wildlife habitats has become important to forest ecosystem management because it provides valuable information about the response of forests and their species to harvest practices, impacts from recreational use, conservation efforts, and natural and human-caused disturbances. Monitoring is a complex task that requires a variety of abiotic and biotic measurements and decisions about what should be measured, and when and where measurements should be taken. Riparian habitats contain unusually high diversity and are important to land managers. Wildlife assessments of riparian areas have focused on vertebrate species such as amphibians, birds, and mammals, but have largely ignored the arthropod components of the habitats. Arthropods constitute over 85% of all species and posses characteristics that make them valuable for tracking environmental changes. The purpose of this study was to gather site-specific data about epigaeic, riparian beetle community composition of the H.J. Andrews Experimental Forest (HJA). The patterns of beetle distribution, abundance, and diversity were analyzed and the results were used to characterize and compare the riparian and adjacent upslope beetle communities. Almost 8,000 beetle specimens representing about 250 species were collected from 141 pitfall traps placed along 10 transects in 3 different channel morphologies along Lookout Creek in the HJA. Traps were opened during six 30-day sampling periods over 2 years. Riparian and adjacent upslope beetle communities had high diversity measurements. The average difference of the calculated Simpson's Diversity Index between the two communities was 0.0116 and represented about 1% of the average riparian diversity. Analysis of species-curves indicated that the riparian habitats contained a higher total number of species. Multivariate Principal Coordinate Analysis indicated that the two habitats had distinctly different beetle communities. Multigroup Discriminant Analysis correctly classified 89.7% of the sampling units as the habitat group into which they were assigned a priori. Detailed recommendations for monitoring riparian habitats were discussed. / Graduation date: 2000

This study describes the composition of forest landscapes surrounding northern spotted owl (Strix occidentalis caurina) nests in the central Cascade Mountains of Oregon. I compared forest composition around 126 owl nests in 70 pair territories with forest composition around 119 points drawn randomly from all terrestrial cover-types, and around 104 points drawn randomly from the old-forest (closed canopy, > 80 yrs) cover type. All nest sites and random points were drawn from U.S. Forest Service lands and were not drawn from privately owned lands or Wilderness Areas. Forest cover was classified on a Landsat Thematic Mapper image. I quantified the percentage of old-forest within 200 concentric circular plots (0.04-5.0-km radii), centered on each analyzed point, using a geographic information system. I used logistic regression to make spatially-explicit inferences. Owl nests were surrounded by more old-forest when compared to points drawn randomly from all terrestrial cover types: there was significantly (P<0.05) more old-forest around the owl nests in plots as large as 1.79 km in radius. When compared to points drawn randomly from the old-forest cover type, owl nests were surrounded by significantly (P<0.05) more old-forest in plots with 0.17-0.80-km radii. Exploratory analyses suggest that the landscape scales most pertinent to northern spotted owl nest site positioning in this study area appear to be (in descending order): the surrounding 10-15 ha (~200-m radius), the surrounding 25-30 ha (~300-m radius), the surrounding 200 ha (800-m radius), and possibly the surrounding 700 ha (1,500-m radius). This study supports the assertion that northern spotted owls are strongly associated with older forests. The results also indicate that owl nests are most associated with higher proportions of old-forest near the nest implying that the arrangement of habitat is important for nest-site selection/positioning Since spotted owls in the central Cascade Mountains of Oregon are known to have home-ranges that average 1,769 ha, it is important to recognize that these results apply to nest-site selection/positioning on the landscape and not to the amount of habitat necessary for pair persistence or successful reproduction. / Graduation date: 1998