Master of Science in Mechanical Engineering (MSME)
Gas turbine efficiency can be improved by increasing the turbine inlet temperature. Secondary flows created in the turbine blade passage cause pressure losses and increase the thermal blade loading on the endwall, thus limiting the combustion temperature. Pressure losses, or aerodynamic losses, extract energy from the fluid, leaving less for torque or thrust production. Secondary flows also cause greater non-uniformity in the exit flow from each blade stage, which decreases the stage efficiency. Weakening secondary flows will lower pressure losses and endwall heat transfer. The following research will explore concepts for weakening the secondary flows through the use of (a) leading edge fillets, and (b) non-axisymmetric endwall contouring for both uncooled and film cooled endwalls in a low speed linear turbine blade cascade. Leading edge fillets are surface shape modifications at the blade’s leading edge and endwall junction. It is designed to reduce the strength of the horseshoe vortex which is the first element of secondary flows. Non-axisymmetric endwall contouring changes the normally flat endwall between each blade to a three dimensional shape. It is designed to reduce the cross passage pressure gradient that drives the crossflow, another part of the secondary flows. Film cooling injects cooler fluid on the endwall through small holes. Its goal is to keep the endwall cool, but the secondary flow vortex structures interact with these coolant jets and adversely affect their performance. Therefore their strategic locations are important for optimal performance of the coolant jets. In this thesis, the effect of leading edge fillets and endwall contouring on the secondary flow is examined with smoke flow visualization, hot wire anemometry, five-hole pressure probe, surface static pressures, and air temperature measurements. Overall, the non-axisymmetric endwall contour reduces the mass averaged pressure losses across the blade passage the most, by 53%. Endwall contouring also produces a much more uniform exit flow field. Film cooling slightly increases pressure losses on the contoured endwall, but losses remain below that of the baseline case. The type of leading edge fillets tested had little effect on overall losses and in some cases actually had a negative effect.
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Gustafson, Ross James, "Flow and temperature measurements in a linear turbine blade passage with leading edge and endwall contouring and with and without film cooling" (2005). LSU Master's Theses. 2308.