Research Papers

Experimentally Measured Effects of Incidence Angle on the Adiabatic and Overall Effectiveness of a Fully Cooled Turbine Airfoil With Shaped Showerhead Holes

[+] Author and Article Information
Kyle Chavez

Department of Mechanical Engineering,
The University of Texas at Austin,
Austin, TX 78712
e-mail: Kyle.F.Chavez@utexas.edu

Thomas N. Slavens

Pratt & Whitney,
East Hartford, CT 06118
e-mail: Thomas.Slavens@pw.utc.com

David Bogard

Department of Mechanical Engineering,
The University of Texas at Austin,
Austin, TX 78712
e-mail: dbogard@mail.utexas.edu

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received January 22, 2017; final manuscript received February 14, 2017; published online April 19, 2017. Editor: Kenneth Hall.

J. Turbomach 139(9), 091007 (Apr 19, 2017) (10 pages) Paper No: TURBO-17-1013; doi: 10.1115/1.4036200 History: Received January 22, 2017; Revised February 14, 2017

Manufacturing and assembly variation can lead to shifts in the inlet flow incidence angles of a rotating turbine airfoil row. Understanding the sensitivity of the adiabatic film cooling effectiveness to a range of inlet conditions is necessary to verify the robustness of a cooling design. In order to investigate the effects of inlet flow incidence angles, adiabatic and overall effectiveness data were measured in a low speed linear cascade at 0 deg and 10 deg of the designed operating condition. Tests were completed at an inlet Reynolds number of Re = 120,000 and a turbulence intensity of Tu = 5% at the leading edge of the test article. Particle image velocimetry was used to verify the incident flow angle for each angle studied. The test section was first adjusted so that the pressure distribution and stagnation line of the airfoil matched those predicted by an aerodynamic computational fluid dynamics (CFD) model. IR thermography was then used to measure the adiabatic effectiveness levels of the fully cooled airfoil model with nine rows of shaped holes of varying construction and feed delivery. Measurements were taken over a range of blowing ratios and at a density ratio of DR = 1.23. This process was repeated for the two incidence angles measured, while the inlet pressure to the airfoil model was held constant for these incidence angle changes. Differences in laterally adiabatic effectiveness across the airfoil model were most evident in the showerhead, with changes as large as 0.2. The effect persisted most strongly at s/D = ±35 downstream of the stagnation row of holes, but was visible over the whole viewable area of 160 s/D. The effect was due to the stagnation line affecting the film at the showerhead row. Due to this effect, the showerhead was investigated in detail, including the effects of the stagnation line shift as well as the influence of the incidence angle on the overall effectiveness of the showerhead region. It was found that the stagnation line has the tendency to dramatically increase the near-hole adiabatic effectiveness levels when positioned within the breakout footprint of the hole. The effect persisted for the overall effectiveness study, since the hole spacing for this particular configuration was wide enough that the through hole convection was not completely dominant. This is the first study to present measured effectiveness values over both the pressure- and suction-side surfaces of a fully cooled airfoil for appreciably off-nominal incidence angles as well as examine adiabatic and overall effectiveness levels for a conical stagnation row of holes.

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Fig. 1

Schematic of turbine airfoil cascade facility with upstream turning vanes to control approach flow angle: A—turning vanes (stage 1), B—turning vanes (stage 2), C—adjustable blockage, D—U-bend bypass, E—adjustable walls, F—test article, and G—turbulence grid

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Fig. 2

Cp predictions and measurements in the leading edge region of the airfoil model

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Fig. 3

(Left) airfoil coordinate system. (Right) locations of film cooling holes and internal passages.

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Fig. 4

Schematic of the wind tunnel coolant loop

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Fig. 5

Camera locations, with triangles indicating cameras on top of the tunnel, and squares indicating cameras beside the tunnel

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Fig. 6

(Top) adiabatic effectiveness measurements of the airfoil, i= 0 deg, I  = 4.74 with the stagnation line shown. (Middle) adiabatic effectiveness measurements of the airfoil, i  = −9 deg, I  = 4.74 with the stagnation line shown. (Bottom) difference in adiabatic effectiveness at the two different incidence angles for I  = 4.74.

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Fig. 7

Δη¯ versus s/D for all momentum flux ratios

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Fig. 8

η for multiple stagnation line positions, showing the effects of stagnation line on conical holes

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Fig. 9

η¯¯ for multiple stagnation line positions, showing the effects of stagnation line on the effectiveness of the showerhead

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Fig. 10

Laterally averaged adiabatic effectiveness levels for the five stagnation line positions at the average momentum flux ratio condition I=4.74

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Fig. 11

(Top) Adiabatic effectiveness measurements for the i=0 and i=−9 angles at condition I=4.74. (Bottom) Overall effectiveness measurements for the i=0 and i=−9 angles at condition I=4.74.

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Fig. 12

Laterally averaged ϕ for the two incidence angles studied (I = 4.74)



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