Aircraft engine manufacturers strive for greater performance and efficiency by continually increasing the turbine inlet temperature. High turbine inlet temperatures significantly degrade the lifetime of components in the turbine. Modern gas turbines operate with turbine inlet temperatures well above the melting temperature of key turbine components. Without active cooling schemes, modern turbines would fail catastrophically. This study will evaluate a novel cooling scheme for turbine airfoils, called microcircuit cooling, in which small cooling channels are located extremely close to the surface of a turbine airfoil. Coolant bled from the compressor passes through the microcircuits and exits through film cooling slots. On further cooling benefit is that the microcircuit passages are filled with irregular pin fin features that serve to increase convective cooling through the channels. Results from this study indicate a strong interaction between the internal microcircuit features and the external film-cooling from the slot exit. Asymmetric cooling patterns downstream of the slot resulted from the asymmetric pin fin design within the microcircuit. Adiabatic effectiveness levels were found to be optimum for the slot design at a blowing ratio of 0.37. The pin fin arrangement along with the impingement cooling at the microcircuit entrance increased the area-averaged heat transfer by a factor of three, relative to an obstructed channel, over a Reynolds range of 5,000 to 15,000. / Master of Science

The heat transfer and friction augmentation in the fully developed portion of a 2:1 aspect ratio rectangular channel with orthogonal ribs at channel Reynolds numbers of 20,000, 30,000, and 40,000 is studied both experimentally and computationally. Ribs are applied to the two opposite wide walls. The rib aspect ratio is varied systematically at 1, 3, and 5, with a constant rib height and constant rib pitch (rib-pitch-to-rib-height ratio of 10). The purpose of the study is to extend the knowledge of the performance of rectangular channels with ribs to include high aspect ratio ribs. The experimental investigation is performed using transient Thermochromic Liquid Crystals technique to measure the distribution of the local Nusselt numbers on the ribbed walls. Overall channel pressure drop and friction factor augmentation is also obtained with the experimental setup. A numerical simulation is also performed by solving the 3-D Reynolds-averaged Navier-Stokes equations using the realizable-k-Greek lowercase letter episilon] turbulence model for closure. Flow visualization is obtained from the computational results as well as numerical predictions of local distributions of Nusselt numbers and overal channel pressure drop. Results indicate that with increasing rib width, the heat transfer augmentation of the ribbed walls decreases with a corresponding reduction in channel pressure drop.