This paper presents the results of an experimental study that investigates the effects of uniform/waveform tip injection along the camberline on the total pressure loss and wake flow characteristics downstream of a row of Low Pressure Turbine (LPT) blades. The experiments are performed in a low speed cascade facility. This injection technique involves spanwise jets at the tip that are issued from a series of holes along the camber line normal to the freestream flow direction. The injection mass flow rate from each hole is individually controlled using computer driven solenoid valves and therefore the flow injection geometrical pattern at the tip can be adjusted to any desired waveform shape, and can be uniform as well as waveform along the camber. Measurements involve Kiel probe traverses for different injection scenarios 0.5 axial chords downstream of the blades as well as Time-Resolved Particle Image Velocimetry (Tr-PIV) measurements at different spanwise locations. Results show that tip injection significantly reduces the total pressure loss levels created by the leakage vortex. Highest overall loss reduction occurs in the case of reversed-triangular injection. The least effective waveform is triangular injection. Loss levels do not seem to get reduced significantly in the passage vortex zone. Velocity, vorticity and turbulence fields created by the passage and leakage vortices get influenced by tip injection. There is significant reduction in the extent of the low momentum zone of the leakage vortex with injection. This effect is much less pronounced for the passage vortex. On the other hand, complex flow patterns are observed within the passage vortex, especially in the case of reversed-triangular injection, such as a possible embedded vortical structure along the passage vortex core, which creates double peaks in the velocity and turbulent kinetic energy fields and complex patterns in Reynolds shear stress.
Experimental Investigation of the Effects of Waveform Tip Injection in a Low Pressure Turbine Cascade
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Mercan, B, Doğan, E, Ostovan, Y, & Uzol, O. "Experimental Investigation of the Effects of Waveform Tip Injection in a Low Pressure Turbine Cascade." Proceedings of the ASME Turbo Expo 2012: Turbine Technical Conference and Exposition. Volume 8: Turbomachinery, Parts A, B, and C. Copenhagen, Denmark. June 11–15, 2012. pp. 1473-1485. ASME. https://doi.org/10.1115/GT2012-69316
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