An experiment was conducted in a linear cascade of Pratt and Whitney Pak-B turbine 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 (t/g) and gap-to-chord (g/c) ratios on the tip-gap flow behavior. Two extreme g/c ratios of 5% and 8% were chosen, for which four tip t/g ratios were simulated using pressure-side winglets. 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 t/g and g/c cases was documented. The intention was to examine any sensitivity of the flow to the g/c ratio that might be attributed to the t/g ratio in a manner that can be categorized as “thick” or “thin” blade behavior. For this, the focus was on possible changes in the size and location of separation and reattachment lines on the blade tip end. The results presented in this paper indicate that the behavior of the flow in the tip-gap region of a linear cascade turbine blade depend both on t/g and the g/c ratios. Downstream loss coefficients generally decreased with increasing t/g for the 5% g/c case, while they were relatively steady with a slight increase with increasing t/g for the 8% g/c case. The squealer reduced pressure loss coefficient for both g/c cases. It was seen to have a peak effectiveness at t/g of about 3.7 for the 5% g/c case, and at t/g of 3.3 for the 8% g/c case, with diminishing effectiveness at larger t/g ratios. Blade loading showed similar dependence on both g/c and t/g. For the baseline flat-tip case, the tip loading initially decreased with increasing t/g up to about 3.5. For values greater than 3.5, the tip loading increased slightly. The addition of the squealer tip increased the tip loading for all of the t/g ratios at the 5% g/c ratio. The trend with t/g generally followed that of the baseline flat-tip case. However, for the 8% g/c case, the blade loading increased almost linearly with increasing t/g, and the squealer increased loading at the smallest t/g but decreased loading for all other t/g cases investigated. In all cases regardless of the t/g, the surface flow visualization revealed a well defined separation and reattachment region. However, the chordwise location of the start of the separation moved toward the trailing edge with increasing t/g and, independently, with increasing g/c. Therefore, no “thick” or “thin” blade regimes were found, and flow characteristics were determined to depend on both g/c and t/g ratios.

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