Browsing by Subject "Turbine"
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Item Experimental investigation of film cooling and thermal barrier coatings on a gas turbine vane with conjugate heat transfer effects(2013-05) Kistenmacher, David Alan; Bogard, David G.In the United States, natural gas turbine generators account for approximately 7% of the total primary energy consumed. A one percent increase in gas turbine efficiency could result in savings of approximately 30 million dollars for operators and, subsequently, electricity end-users. The efficiency of a gas turbine engine is tied directly to the temperature at which the products of combustion enter the first stage, high-pressure turbine. The maximum operating temperature of the turbine components’ materials is the major limiting factor in increasing the turbine inlet temperature. In fact, current turbine inlet temperatures regularly exceed the melting temperature of the turbine vanes through advanced vane cooling techniques. These cooling techniques include vane surface film cooling, internal vane cooling, and the addition of a thermal barrier coating (TBC) to the exterior of the turbine vane. Typically, the performance of vane cooling techniques is evaluated using the adiabatic film effectiveness. However, the adiabatic film effectiveness, by definition, does not consider conjugate heat transfer effects. In order to evaluate the performance of internal vane cooling and a TBC it is necessary to consider conjugate heat transfer effects. The goal of this study was to provide insight into the conjugate heat transfer behavior of actual turbine vanes and various vane cooling techniques through experimental and analytical modeling in the pursuit of higher turbine inlet temperatures resulting in higher overall turbine efficiencies. The primary focus of this study was to experimentally characterize the combined effects of a TBC and film cooling. Vane model experiments were performed using a 10x scaled first stage inlet guide vane model that was designed using the Matched Biot Method to properly scale both the geometrical and thermal properties of an actual turbine vane. Two different TBC thicknesses were evaluated in this study. Along with the TBCs, six different film cooling configurations were evaluated which included pressure side round holes with a showerhead, round holes only, craters, a novel trench design called the modified trench, an ideal trench, and a realistic trench that takes manufacturing abilities into account. These film cooling geometries were created within the TBC layer. Each of the vane configurations was evaluated by monitoring a variety of temperatures, including the temperature of the exterior vane wall and the exterior surface of the TBC. This study found that the presence of a TBC decreased the sensitivity of the thermal barrier coating and vane wall interface temperature to changes in film coolant flow rates and changes in film cooling geometry. Therefore, research into improved film cooling geometries may not be valuable when a TBC is incorporated. This study also developed an analytical model which was used to predict the performance of the TBCs as a design tool. The analytical prediction model provided reasonable agreement with experimental data when using baseline data from an experiment with another TBC. However, the analytical prediction model performed poorly when predicting a TBC’s performance using baseline data collected from an experiment without a TBC.Item Experimental investigation of overall effectiveness and coolant jet interactions on a fully cooled C3X turbine vane(2013-05) McClintic, John W; Bogard, David G.This study focused on experimentally measuring the performance of a fully cooled, scaled up C3X turbine vane. Experimental measurements focused on investigating row-to-row interactions of coolant jets and the contributions of external film cooling and internal impingement cooling to overall cooling effectiveness. Overall effectiveness was experimentally measured using a thermally scaled, matched Biot number vane model featuring a realistic internal impingement scheme and had normalized surface temperatures that were representative of those found on engine components. A geometrically identical vane was also constructed out of low conductivity polystyrene foam to measure the normalized adiabatic wall temperature, or adiabatic effectiveness of the film cooling configuration. The vanes featured a full coverage film-cooling scheme with a five-row showerhead and 13 total rows of holes containing 149 total coolant holes. This study was the first study to make highly detailed measurements of overall effectiveness on a fully-cooled vane model and expands on previous studies of adiabatic and overall effectiveness on the showerhead and single rows of holes on a matched Biot vane by considering a fully cooled configuration to determine if the results from these previous studies also hold for a fully cooled configuration. Additionally, velocity and thermal fields were measured just upstream of two different suction side rows of holes in order to study the effect of introducing upstream coolant injection. The effects of mainstream turbulence and span-wise location were examined and at the downstream row of holes, the contributions of different rows of holes to the approach flow were compared. This study was the first to measure mean and fluctuating velocity data on the suction side of a turbine vane with upstream coolant injection. Understanding the effects of how upstream injection affects the performance of downstream rows of holes is critical to understanding the film cooling performance on a fully cooled turbine airfoil.Item An experimental study of film cooling, thermal barrier coatings and contaminant deposition on an internally cooled turbine airfoil model(2012-05) Davidson, Frederick Todd; Bogard, David G.; Kiehne, Thomas M.; Kohli, Atul; Ezekoye, Ofodike A.; Webber, Michael E.Approximately 10% of all energy consumed in the United States is derived from high temperature gas turbine engines. As a result, a 1% increase in engine efficiency would yield enough energy to satisfy the demands of approximately 1 million homes and savings of over $800 million in fuel costs per year. Efficiency of gas turbine engines can be improved by increasing the combustor temperature. Modern engines now operate at temperatures that far exceed the material limitations of the metals they are comprised of in the pursuit of increased thermal efficiency. Various techniques to thermally protect the turbine components are used to allow for safe operation of the engines despite the extreme environments: film cooling, internal convective cooling, and thermal barrier coatings. Historically, these thermal protection techniques have been studied separately without account for any conjugate effects. The end goal of this work is to provide a greater understanding of how the conjugate effects might alter the predictions of thermal behavior and consequently improve engine designs to pursue increased efficiency. The primary focus of this study was to complete the first open literature, high resolution experiments of a modeled first stage turbine vane with both active film cooling and a simulated thermal barrier coating (TBC). This was accomplished by scaling the thermal behavior of a real engine component to the model vane using the matched Biot number method. Various film cooling configurations were tested on both the suction and pressure side of the model vane including: round holes, craters, traditional trenches and a novel modified trench. IR thermography and ribbon thermocouples were used to measure the surface temperature of the TBC and the temperature at the interface of the TBC and vane wall, respectively. This work found that the presence of a TBC significantly dampens the effect of altering film cooling conditions when measuring the TBC interface temperature. This work also found that in certain conditions adiabatic effectiveness does not provide an accurate assessment of how a film cooling design may perform in a real engine. An additional focus of this work was to understand how contaminant deposition alters the cooling performance of a vane with a TBC. This work focused on quantifying the detrimental effects of active deposition by seeding the mainstream flow of the test facility with simulated molten coal ash. It was found that in most cases, except for round holes operating at relatively high blowing ratios, the performance of film cooling was negatively altered by the presence of contaminant deposition. However, the cooling performance at the interface of the TBC and vane wall actually improved with deposition due to the additional thermal resistance that was added to the exterior surface of the model vane.Item Experimentally determined external heat transfer coefficient of a turbine airfoil design at varying incidence angles(2015-05) Packard, Gavin Ray; Bogard, David G.; Hall, Mathew JPredicting and measuring external heat transfer coefficients of hot gas path turbine components are important tools for gas turbine designers. Inlet temperatures often exceed the melting temperature of the materials used in such components, requiring protective measures such as thermal barrier coatings or film-cooling to prevent component failure. The external heat transfer coefficients can be used to design for the thermal loading that will ultimately lead to such failures. Modern engine designers use computational codes to predict the conditions of the hot gas components during engine operation. Before these codes can be relied upon as accurate, they must first be verified with experimental measurements. However, measuring the heat transfer coefficients can be a difficult process, especially on an actual engine component, due to the extreme temperatures and inaccessibility. As such, low speed, low temperature wind tunnels are often used to simulate a scaled version of turbine components to collect experimental data to assist in validating computational codes. This thesis details the construction of scaled up turbine airfoils to collect such data. It also provides data covering the generation of turbulence using an array of vertical rods upstream of a linear cascade in a low speed wind tunnel at off-normal incidence flow angles.Item Hydrodynamic optimization and design of marine current turbines and propellers(2013-08) Menéndez Arán, David Hernán; Kinnas, Spyros A.This thesis addresses the optimization and design of turbine and propeller blades through the use of a lifting line model. An existing turbine optimization methodology has been modified to include viscous terms, non-linear terms, and a hub model. The method is also adapted to the optimization of propellers. Two types of trailing wake geometries are considered: one based on helical wakes which are aligned at the blade (using the so-called "moderately loaded propeller'' assumption), and a second one based on a full wake alignment model in order to represent more accurately the wake geometry and its effect on the efficiency of the rotor. A comparison of the efficiencies and the loading distributions obtained through the present methods is presented, as well as convergence and numerical accuracy studies, and comparisons with existing analytical results. In the case of turbines, various types of constraints are imposed in the optimization method in order to avoid abrupt changes in the designed blade shape. The effect of the constraints on the efficiency of the turbines is studied. Once the optimum loading has been determined, the blade geometry is generated for given chord, thickness and camber distributions. Finally, a low-order potential-based boundary element method and a vortex-lattice method are used to verify the efficiency of the designed turbines.Item Systematic study of shaped-hole film cooling at the leading edge of a scaled-up turbine blade(2020-05-14) Moore, Jacob Damian; Bogard, David G.; Oliver, Todd A; Ezekoye, Ofodike A; Ellzey, Janet LThe leading-edge regions of turbine vanes and blades require careful attention to their cooling designs because of the high heat loads. External cooling is typically accomplished with dense "showerhead" arrangements of film cooling holes surrounding the stagnation point at the airfoil leading edge. In modern film cooling studies, shaped holes are prevalent in downstream areas of turbine airfoils; however, the literature contains few studies of shaped holes in the showerhead. This leads to a lack of physics-based insight that would lead to the design of high-performing showerhead arrays. This study examined the performance and physical behavior of several showerhead arrangements at the leading edge of a scaled-up turbine blade. A low-speed linear cascade test section was used to simulate the blade environment, and experiments were conducted at scaled engine-realistic conditions. First, the cooling performances of baseline cylindrical and shaped hole designs were compared. The shaped hole design mimicked a standard design in the literature for flat plate studies but with some modifications expected to improve performance specifically at the leading edge. The result was a novel off-center, elliptically-expanding hole. Adiabatic effectiveness and thermal field measurements revealed that the baseline shaped hole had 20-100% performance due to better jet attachment, stemming from its diffuser, which effectively decreased the exit momenta of the coolant jets. The expansion area ratio was increased by 40% for a subsequent design to gauge sensitivity to this parameter; but, surprisingly, the performances of the new design and of the baseline one were nearly identical. A third shaped hole design with a 45% larger breakout area but an identical expansion area resulted in slightly worse performance than either, highlighting the detrimental effect of increasing breakout area and expansion angle. These experiments informed a new proposed scaling parameter incorporating both of these areas and their counteracting effects to predict shaped hole performance in the showerhead. The highest performing design of the group was then tested with an engine-realistic impingement coolant feed, for which performance was overall similar. Supplemental thermal fields using this configuration were performed to construct a 3D representation of the flow field in the showerhead region.Item Texas offshore wind power and water desalination potential(2015-05) Beceiro, Jose Daniel; Spence, David B.; Webber, Michael E., 1971-Texas leads the nation in oil and gas production as well as renewable energy production. Texas also leads the nation in installed wind power and is the 6th largest wind market in the world. Over the past decade, Texas has gone from nearly zero megawatts of installed wind to now over 14,000 megawatts. Texas has an immense onshore wind resource that has been exploited. However, another of Texas' large untapped energy resources has yet to be explored -- offshore wind. Texas is also experiencing one of the most severe and longest sustained drought cycles in the state's history. Texas is blessed with a vast supply of ocean water and brackish groundwater trapped in aquifers, but energy-intensive water desalination plants are required to purify the water to potable standards. Offshore wind has the ability to turn large-scale water desalination into an economical solution. This thesis focuses on offshore wind and water desalination technology development, cost competitiveness with competing renewable energy and thermo electric generation resources on the ERCOT nodal grid, and the opportunity to couple water desalination facilities with offshore wind farms to enhance overall project economics, reduce the cost of electricity, and increase the supply of fresh water. An economic model evaluating offshore wind-powered water desalination is utilized to demonstrate the viability of implementing these technologies across the state.