Browsing by Subject "Turbine vane"
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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 Measurements of adiabatic effectiveness from full coverage film cooling on a scaled turbine vane with laidback fanshaped holes(2017-09-22) O'Neal, Owen Michael; Bogard, David G.; Crawford, MIchaelThis study was focused on measurements of adiabatic effectiveness on a scaled turbine vane which made use of a contoured endwall to match engine conditions. The vane model featured a full coverage film-cooling configuration with five rows of cylindrical holes in the showerhead and ten rows of laidback fanshaped holes distributed on the pressure and suction sides. The vane model was tested across a wide range of blowing ratios in several different coolant configurations including: individual rows on the pressure and suction side, full coverage tests with and without showerhead cooling, and full coverage tests at low and high mainstream turbulence levels. Comparisons between these configurations were made in order to assess the effects of local curvature, showerhead cooling, and mainstream turbulence levels. Single row tests measured in areas of high convex curvature tended to have an improved performance relative to flat plate predictions, while the opposite was true for rows in areas of concave curvature. Overall, showerhead cooling did not provide any significant improvements in effectiveness far downstream on both the pressure and suction side. Increasing mainstream turbulence levels tended to diminish the film cooling effectiveness. The negative effect of higher mainstream turbulence was most significant at low blowing ratios, but became negligible at higher flow rates.Item Rough wall and near-hole obstruction effects on film cooling with and without a transverse trench(2006-12) Somawardhana, Ruwan Prasanna; Bogard, David G.Significant degradation of adiabatic effectiveness can be caused by surface roughness and near-hole obstructions formed from deposition of contaminants. Since obstructions are a randomly occurring event, there are many variables to consider, namely shape, width, length, height, and position in relation to a film cooling hole. In addition to this, the level of overall surface roughness must also be considered. This study investigated these different variables on the suction side of a scaled-up turbine vane using cylindrical holes to determine what is important when considering surface roughness and obstructions. In addition, the use of a transverse trench was tested with a rough wall and near-hole obstructions and was found to be a method to mitigate a large part of the degrading effects caused by a rough surface and near-hole obstructions.Item Roughness impact on turbine vane suction side film cooling effectiveness(2004-05-22) Robertson, David Richard; Bogard, David G.This study investigates the effect that surface roughness has on the adiabatic effectiveness performance of the first row of suction side cooling holes on a turbine inlet guide vane. The effects of roughness placement (roughness upstream, downstream, or combined up and downstream of the row of film cooling holes) are investigated. Additionally, for each roughness placement, the effect of mainstream turbulence level and showerhead coolant will be quantified. To gain insight into the state of the boundary layer just upstream of the row of film cooling holes, a hot-wire anemometer will be used to measure the velocity and turbulence profiles that exist under various conditions. It was found that roughness degrades the adiabatic effectiveness performance of low blowing ratios and enhances the adiabatic effectiveness performance of high blowing ratios. Roughness also shifts the optimum blowing ratio, toward higher coolant flow rates. Roughness thickens the boundary layer and increases its turbulence intensityItem Suction side roughness effects on film cooling heat transfer on a turbine vane(2004-05-22) Rutledge, James Lloyd; Bogard, David G.An experimental study was conducted in a simulated three vane linear cascade to determine the effects of surface roughness and film cooling on the heat transfer coefficient distribution in the region downstream of the first row of suction side coolant holes. Suction side film cooling was operated in the range 0 = M = 1.4. The showerhead was tested at Msh = 1.6. In addition to the completely smooth condition, simulated airfoil roughness was used upstream of the coolant holes, downstream of the coolant holes, and both upstream and downstream of the coolant holes. Two levels of mainstream turbulence intensity were tested. The heat transfer measurements were conducted by application of a uniform heat flux in the region downstream of the coolant holes. The resulting surface temperature distributions were measured with infrared thermography. Because the upstream region was unheated, the influence of film cooling on the heat transfer coefficient was due to only to hydrodynamic effects and not thermal effects. The coolant to mainstream density ratio of the majority of the experiments was unity; however, a single experiment was conducted at a density ratio of DR = 1.6 to determine how the coolant to mainstream density ratio affects heat transfer. Net heat flux reduction calculations were performed by combining the heat transfer coefficient measurements of the present study with adiabatic effectiveness measurements of a separate study. In order to gain insight into the hydrodynamics that affect the heat transfer, boundary layer measurements were conducted using hot-wire anemometry