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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
301

An Investigation of Heat Transfer Coefficient and Film Cooling Effectiveness in a Transonic Turbine Cascade

Smith, Dwight E. 14 August 1999 (has links)
This study is an investigation of the film cooling effectiveness and heat transfer coefficient of a two-dimensional turbine rotor blade in a linear transonic cascade. Experiments were performed in Virginia Tech's Transonic Cascade Wind Tunnel with an exit Mach number 0f 1.2 and an exit Reynolds numbers of 5x106 to simulate real engine flow conditions. The freestream and coolant flows were maintained at a total temperature ratio of 2(+,-)0.4 and a total pressure ratio of 1.04. The freestream turbulence was approximately 1%. There are six rows of staggered, discrete cooling holes on and near the leading edge of the blade in a showerhead configuration. Cooled air was used as the coolant. Experiments were performed with and without film cooling on the surface of the blade. The heat transfer coefficient was found to increase with the addition of film cooling an average of 14% overall and to a maximum of 26% at the first gauge location. The average film cooling effectiveness along the chord-wise direction of the blade is 25%. Trends were found in both the uncooled and the film-cooled experiments that suggest either a transition from a laminar to a turbulent film regime or the existence of three-dimensionality in the flow-field over the gauges. / Master of Science
302

Investigation of Aerodynamic Profile Losses for a Low-Reaction Steam Turbine Blade

Guilliams, Hunter Benjamin 27 January 2014 (has links)
This thesis presents the results of a linear cascade experiment performed on the mean-line and near-tip sections of a low-reaction steam turbine blade and compares them to CFD of the former. The purpose of these tests was the refinement of a proprietary empirical profile loss model. A review of the literature shows that experimental data on this type of blade is not openly available. The continued efficacy of empirical loss models to low-reaction steam turbine blades requires data from experiments such as the present study. Tests covered a range of incidence from -6 to +4 and exit Mach numbers from 0.4 to 0.6. Extensive static pressure taps on the blades allowed detailed examinations of blade loading. This loading was dissimilar to steam turbine blade loading in the open literature. A traversing five-hole probe measured conditions downstream of the blade row to enable the calculation of a total pressure loss coefficient. The area-averaged total pressure loss coefficient for both profiles was near 0.08 and was not sensitive to incidence or exit Mach number over the ranges tested. / Master of Science
303

Simulation of Isothermal Combustion in Gas Turbines

Rice, Matthew Jason 24 February 2004 (has links)
Current improvements in gas turbine engine performance have arisen primarily due to increases in turbine inlet temperature and compressor pressure ratios. However, a maximum possible turbine inlet temperature exits in the form of the adiabatic combustion temperature of the fuel. In addition, thermal limits of turbine blade materials also places an upper bound on turbine inlet temperatures. Thus, the current strategy for improving gas turbine efficiency is inherently limited. Introduction of a new gas turbine, based on an alternative work cycle utilizing isothermal combustion (i.e. combustion within the turbine) affords significant opportunities for improving engine output and/or efficiency. However, implementation of such a scheme presents a number of technological challenges such as holding a flame in high-speed flow. The current research is aimed at determining whether such a combustion scheme is feasible using computational methods. The geometry, a simple 2-D cascade utilizes surface injection within the stator or rotor boundary layers (including the rotor pressure side recirculation zone (a natural flame holder). Computational methods utilized both steady and time accurate calculations with transitional flow as well as laminar and turbulent combustion and species transport. It has been determined that burning within a turbine is possible given a variety of injection schemes using "typical" foil geometries under "typical" operating conditions. Specifically, results indicate that combustion is self-igniting and, hence, self-sustaining given the high temperatures and pressures within a high pressure turbine passage. Deterioration of aerodynamic performance is not pronounced regardless of injection scheme. However, increased thermal loading in the form of higher adiabatic surface temperatures or heat transfer is significant given the injection and burning of the fuel within the boundary layer. This increase in thermal loading is, however, minimized when injection takes place in or near a recirculation zone. The effect of injection location on pattern factors indicates that suction side injection minimizes temperature variation downstream of the injection surface (for rotor injection only). In addition, the most uniform temperature profile (in the flow direction) is achieved by injection fuel and combustion nearest to the source of work extraction. Namely, injection at the rotor produces the most "isothermal" temperature distribution. Finally, a pseudo direct simulation of an isothermal machine is conducted by combining simulation data and assumed processes. The results indicate that isothermal combustion results in an increase in turbine specific work and efficiency over the equivalent Brayton cycle. / Master of Science
304

An Investigation of Effectiveness of Normal and Angled Slot Film Cooling in a Transonic Wind Tunnel

Hatchett, John Henry 04 March 2008 (has links)
An experimental and numerical investigation was conducted to determine the film cooling effectiveness of a normal slot and angled slot under realistic engine Mach number conditions. Freestream Mach numbers of 0.65 and 1.3 were tested. For the normal slot, hot gas ingestion into the slot was observed at low blowing ratios (M < 0.25). At high blowing ratios (M > 0.6) the cooling film was observed to "lift off" from the surface. For the 30o angled slot, the data was found to collapse using the blowing ratio as a scaling parameter (x/Ms). Results from the current experiment were compared with the subsonic data published to confirm this test procedure. For the angled slot, at the supersonic freestream Mach number, the current experiment shows that at the same x/Ms, the film cooling effectiveness increases by as much as 25% as compared to the subsonic case. The results of the experiment also show that at the same x/Ms, the film cooling effectiveness of the angled slot is considerably higher than that of the normal slot, at both subsonic and supersonic Mach numbers. The flow physics for the slot tests considered here are also described with computational fluid dynamic (CFD) simulations in the subsonic and supersonic regimes. / Master of Science
305

The Influence of Pressure Ratio on Film Cooling Performance of a Turbine Blade

Bubb, James Vernon 05 August 1999 (has links)
The relationship between the plenum to freestream total pressure ratio on film cooling performance is experimentally investigated. Measurements of both the heat transfer coefficient and the adiabatic effectiveness were made on the suction side of the center blade in a linear transonic cascade. Entrance and exit Mach numbers were 0.3 and 1.2 respectively. Reynolds number based on chord and exit conditions is 3 x 10⁶. The blade contour is representative of a typical General Electric first stage, high turning, turbine blade. Tunnel freestream conditions were 10 psig total pressure and approximately 80 °C. A chilled air coolant film was supplied to a generic General Electric leading edge showerhead coolant scheme. Pressure ratios were varied from run to run over the ranges of 1.02 to 1.20. The density ratio was near a value of 2. A method to determine both the heat transfer coefficient and film cooling effectiveness from experimental data is outlined. Results show that the heat transfer coefficient is independent of the pressure ratio over these ranges of blowing parameters. Also, there is shown to be a weak reduction of film cooling effectiveness with higher pressure ratios. Results are shown for effectiveness and heat transfer coefficient profiles along the blade. / Master of Science
306

Evaluation of a Heat Flux Microsensor in a Transonic Turbine Cascade

Peabody, Hume L. 26 November 1997 (has links)
The effects of using an insert Heat Flux Microsensor (HFM) versus an HFM deposited directly on a turbine blade to measure heat flux in a transonic cascade are investigated. The HFM is a thin-film sensor, 6.35 mm (0.250") in diameter (for an insert gage, including the housing) which measures heat flux and surface temperature. The thermal time response of both gages was modeled using a 1-D, finite difference technique and a 2-D, finite element solver. The transient response of the directly deposited gage was also tested against insert gages using an unsteady shock wave in a bench test setup and using a laser of known output. The effects of physical gage offset from the blade surface were also investigated. The physical offset of an insert HFM near the stagnation point on the suction side of a turbine blade was intentionally varied and the average heat transfer coefficient measured. Turbulence grids were used to study how offset affects the heat transfer coefficient with freestream turbulence added to the flow. The time constant of the directly deposited gage was measured to be 856 ms compared to less than 30 ms for the insert gages. Model results predict less than 20 ms for both gages and rule out the anodization layer (used for electrical isolation of the directly deposited gage from the blade) as the cause for the directly deposited gage's much slower time response. Offsets of ± 0.254 mm (0.010") at the gage location with an estimated boundary layer thickness of 0.10 mm (0.004") produced a higher average heat transfer coefficient than the 0.000" offset case. Using an insert HFM resulted in a higher average heat transfer coefficient than using the directly deposited gage and reduced the effects of freestream turbulence. To accurately measure heat transfer coefficients and the effects of freestream turbulence, the disruption of the flow caused by a gage must be minimized. Depositing a gage directly on the blade minimizes the effects of offset, but the cause of the slow time response must first be resolved if high speed data is to be taken. / Master of Science
307

Airfoil Self-Noise Prediction Using Neural Networks for Wind Turbines

Errasquin, Leonardo 30 October 2009 (has links)
A neural network prediction method has been developed to compute self-noise of airfoils typically used in wind turbines. The neural networks were trained using experimental data corresponding to tests of several different airfoils over a range of flow conditions. The experimental data corresponds to the NACA 0012, Delft DU96, Sandia S831, S822 and S834, Fx63-137, SG6043 and SD-2030 airfoils. The chord of these airfoils range from 0.025 to 0.91 m and they were tested at Reynolds numbers of up to 3.8 million and angle of attack up to 15° depending on the airfoil. Using experimental data corresponding to different airfoils provides to the neural network the capacity to take into account the geometry of the airfoils in the predictions.geometry of the airfoils in the predictions. The input parameters to the network are the flow speed, chord length, effective angle of attack and parameters describing the geometrical shape of the airfoil. In addition, boundary layer displacement thickness was used for some models. The parameters used for taking into account the airfoil's geometry are based on a conformal mapping method or a polynomial approximation. The output of the neural network is given by sound pressure level in 1/3rd octave bands for nine frequencies ranging from 630 to 4000 Hz. The present work constitutes an application of neural networks to aeroacoustics. The main objective was to assess the potential of using neural networks to model airfoil noise. Therefore, this work is focused in the modeling of the problem, and no mathematical analyses about neural networks are intended. To this end, several models were investigated both in terms of the configuration and training approach. The performance of the networks was evaluated for a range of flow conditions. The neural network technique was first investigated for the NACA 0012 airfoil only. For this case, the geometry of the airfoil was not incorporated as input into the model. The neural network approach was then extended to account for airfoils of any geometry by including data from all airfoils in the training. The results show that the neural networks are capable of predicting the airfoils self-noise reasonably well for most of the flow conditions. The broadband noise due to the turbulent boundary layer interacting with the trailing edge is estimated very well. The tonal vortex shedding noise due to laminar boundary layer-trailing edge interaction is not predicted as well, most likely due to the limited data available for this noise source. In summary, the research here demonstrated the potential of the neural network as a tool to predict noise from typical wind turbine airfoils. / Master of Science
308

An optimal, low-cost design for small wind turbine converters applied to charging batteries

Baker, Jonathan 01 January 2009 (has links)
In the entirety of this project, a power converter is modeled, simulated, designed, and optimized to convert a three-phase AC wind turbine source to charge DC lead-acid batteries, applying new control techniques and an innqvative design to produce the most energy from the small wind turbine. The converter will implement new approaches to power factor correction and maximum power point tracking to capture the most energy under any operating conditions of the wind turbine. Overwind conditions will be protected against using the converter's ability to slow the turbine instead of usual resistive loads or mechanical braking. Other techniques to protect the batteries and the converter will be discussed in the scope of this paper. Through testing the designed converter, supporting evidence is shown whether the topology and control techniques are beneficial by comparing the degree of effectiveness of each method. The goal is to prove that these methods will provide a significant increase in energy converted.
309

Investigation on methods to improve heat loadprediction of the SGT-600 gas turbine

Farhanieh, Arman January 2016 (has links)
In modern gas turbines, with the increase of inlet gas temperature to raise thework output, the importance of accurate aero-thermal analysis has become of vitalimportance. These analysis are required for temperature prediction throughoutthe turbine and to predict the thermal stresses and to estimate the cooling requiredfor each component.In the past 20 years, computational fluid dynamics (CFD) methods have becomea powerfool tool aero-thermal analysis. Due to reasons including numericallimitation, flow complications caused by blade row interactions and the effect offilm cooling, using simple steady state CFD methods may result in inaccuratepredictions. Even though employing transient simulations can improve the accuracyof the simulations, it will also greatly increase the simulation time and cost.Therefore, new methods are constantly being developed to increase the accuracywhile keeping the computational costs relatively low. Investigating some of thesedeveloped methods is one of the main purposes of this study.A simplification that has long been applied in gas turbine simulations hasbeen the absence of cooling cavities. Another part of this thesis will focus onthe effect of cooling cavities and the importance of including them in the domain.Therefore, all transient and steady state simulations have been examined for twocases; a simplified case and a detailed case. The results are then compared tothe experimental measurements to evaluate the importance of their presence inthe model. The software used to perform all simulations is the commercial codeANSYS CFX 15.The findings suggest that even though including cooling cavities would improvethe results, the simulations should be run in transient. One important finding wasthat when performing transient simulations, especially the Time Transformationmethod, not only is the pitch ratio between every subsequent blade row important,but also the pitch ratio between the stators is highly influential on the accuracyof the results.
310

Conception d'une chambre de combustion pour la microturbine à gaz SRGT-2

Fortier-Topping, Hugo January 2014 (has links)
Dans un contexte mondial où les ressources énergétiques commencent à se faire rares, beaucoup de recherches se font sur l’amélioration de l’efficacité thermique et de la densité de puissance des sources d’énergie existantes. Ainsi, un projet de développement d’une microturbine à gaz avec une architecture de nouveau genre permettant d’augmenter la densité de puissance tout en réduisant les coûts a vu le jour. La recherche proposée dans le présent document se concentre sur la conception et la caractérisation d’une chambre de combustion et d’un banc d’essai pour la turbine SRGT-2. Une chambre de combustion à écoulement inverse est conçue et caractérisée expérimentalement. Un modèle 0D de la chambre est tout d’abord fait. Par la suite, une optimisation numérique est faite jusqu’à l’atteinte des objectifs de conception. Finalement, la chambre de combustion est testée durant 30 secondes avec de l’hydrogène comme carburant. Une température de sortie de la chambre de combustion de 1000 K a été maintenue avec une efficacité de combustion de plus de 85%. Le banc d’essai conçu pour le projet de recherche utilise un démarreur électropneumatique permettant d’accélérer le prototype jusqu’à 102 000 RPM. Le module fluide est la partie du banc d’essai qui contient les différentes parties de la turbine SRGT-2 comme le rotor, les stators et la chambre de combustion. Le module est instrumenté dans le but d’obtenir une caractérisation complète de la turbine. Sa configuration modulaire permet aussi de caractériser chacune des composantes individuellement en changeant certaines sections.

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