Turbine Blade Tip Leakage Flow Control: Thick/Thin Blade Effects

An experiment was conducted in a linear cascade of Pak-B blades for an exit Mach number of 0.3 to simulate the flow in the tip-gap region of a low pressure turbine blade row. The experiment focused on the independent effects of thickness-to-gap and gapto-chord ratios on the tip-gap flow behavior. Two extreme gap-to-chord ratios of 5% and 8% were chosen, for which four thickness-to-gap ratios were examined. The flow was documented through blade-tip and end-wall static pressure measurements, and downstream total pressure loss coefficients. Additionally, surface flow visualization was performed on the blade tip end for a greater understanding of the gap-flow behavior. The response of the flow to passive flow control using a partial suction-side squealer tip at each of the thickness-togap and gap-to-chord cases was documented. The intention was to examine any sensitivity of the flow to the gap-to-chord ratio that might be attributed to the thickness-to-gap ratio in a manner that can be categorized as “thick” and “thin” blade behavior. For this the focus was on possible changes in the size and location of a separation and re-attachment lines on the blade tip end. Defining such features in these flows is important to our goal of active tip-gap flow control using plasma actuators because they are highly receptivity to unsteady forcing.