Browsing by Subject "Thermal fields"
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Item Conjugate heat transfer effects on gas turbine film cooling : including thermal fields, thermal barrier coating, and contaminant deposition(2014-05) Stewart, William Robb; Bogard, David G.The efficiency of natural gas turbines is directly linked to the turbine inlet temperature, or the combustor exit temperature. Further increasing the turbine inlet temperature damages the turbine components and limits their durability. Advances in turbine vane cooling schemes protect the turbine components. This thesis studies the conjugate effects of internal cooling, film cooling and thermal barrier coatings (TBC) on turbine vane metal temperatures. Two-dimensional thermal profiles were experimentally measured downstream of a single row of film cooling holes on both an adiabatic and a matched Biot number model turbine vane. The measurements were taken as a comparison to computational simulations of the same model and flow conditions. To improve computational models of the evolution of a film cooling jet as it propagates downstream, the thermal field above the vane, not just the footprint on the vane surface must be analyzed. This study expands these data to include 2-D thermal fields above the vane at 0, 5 and 10 hole diameters downstream of the film cooling holes. In each case the computational jets remained colder than the experimental jets because they did not disperse into the mainstream as quickly. Finally, in comparing results above adiabatic and matched Biot number models, these thermal field measurements allow for an accurate analysis of whether or not the adiabatic wall temperature was a reasonable estimate of the driving temperature for heat transfer. In some cases the adiabatic wall temperature did give a good indication of the driving temperature for heat transfer while in other cases it did not. Previous tests simulating the effects of TBC on an internally and film cooled model turbine vane showed that the insulating effects of TBC dominate over variations in film cooling geometry and blowing ratio. In this study overall and external effectiveness were measured using a matched Biot number model vane simulating a TBC of thickness 0.6d, where d is the film cooing hole diameter. This new model was a 35% reduction in thermal resistance from previous tests. Overall effectiveness measurements were taken for an internal cooling only configuration, as well as for three rows of showerhead holes with a single row of holes on the pressure side of the vane. This pressure side row of holes was tested both as round holes and as round holes embedded in a realistic trench with a depth of 0.6 hole diameters. Even in the case of this thinner TBC, the insulating effects dominate over film cooling. In addition, using measurements of the convective heat transfer coefficient above the vane surface, and the thermal conductivities of the vane wall and simulated TBC material, a prediction technique of the overall effectiveness with TBC was evaluated.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.