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Research Papers

Numerical Investigation of Aerothermal Characteristics of the Blade Tip and Near-Tip Regions of a Transonic Turbine Blade

[+] Author and Article Information
A. Arisi

Mechanical Engineering Department,
Virginia Polytechnic Institute and State University,
Blacksburg, VA 24061
e-mail: arisi@vt.edu

S. Xue

Mechanical Engineering Department,
Virginia Polytechnic Institute and State University,
Blacksburg, VA 24061
e-mail: xuesong@vt.edu

W. F. Ng

Mechanical Engineering Department,
Virginia Polytechnic Institute and State University,
Blacksburg, VA 24061
e-mail: wng@vt.edu

H. K. Moon

Solar Turbines Inc.,
San Diego, CA 92101
e-mail: Moon_Hee_Koo_X@solarturbines.com

L. Zhang

Solar Turbines Inc.,
San Diego, CA 92101
e-mail: Zhang_Luzeng_J@solarturbines.com

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received January 5, 2015; final manuscript received January 28, 2015; published online February 18, 2015. Editor: Ronald Bunker.

J. Turbomach 137(9), 091002 (Sep 01, 2015) (12 pages) Paper No: TURBO-15-1002; doi: 10.1115/1.4029713 History: Received January 05, 2015; Revised January 28, 2015; Online February 18, 2015

In modern gas turbine engines, the blade tips and near-tip regions are exposed to high thermal loads caused by the tip leakage flow. The rotor blades are therefore carefully designed to achieve optimum work extraction at engine design conditions without failure. However, very often gas turbine engines operate outside these design conditions which might result in sudden rotor blade failure. Therefore, it is critical that the effect of such off-design turbine blade operation be understood to minimize the risk of failure and optimize rotor blade tip performance. In this study, the effect of varying the exit Mach number on the tip and near-tip heat transfer characteristics was numerically studied by solving the steady Reynolds averaged Navier Stokes (RANS) equation. The study was carried out on a highly loaded flat tip rotor blade with 1% tip gap and at exit Mach numbers of Mexit = 0.85 (Reexit = 9.75 × 105) and Mexit = 1.0 (Reexit = 1.15 × 106) with high freestream turbulence (Tu = 12%). The exit Reynolds number was based on the rotor axial chord. The numerical results provided detailed insight into the flow structure and heat transfer distribution on the tip and near-tip surfaces. On the tip surface, the heat transfer was found to generally increase with exit Mach number due to high turbulence generation in the tip gap and flow reattachment. While increase in exit Mach number generally raises he heat transfer over the whole blade surface, the increase is significantly higher on the near-tip surfaces affected by leakage vortex. Increase in exit Mach number was found to also induce strong flow relaminarization on the pressure side near-tip. On the other hand, the size of the suction surface near-tip region affected by leakage vortex was insensitive to changes in exit Mach number but significant increase in local heat transfer was noted in this region.

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References

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Figures

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Fig. 1

Numerical computation domain (left) and a section of the tip and near-tip surface mesh (right)

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Fig. 2

Midspan blade loading for Mexit = 0.85 with 1% tip gap clearance

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Fig. 3

Midspan HTC predicted by CFD (Mexit = 0.85). Experiment data measured by Nasir et al. [25] (Mexit = 0.78).

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Fig. 4

Near-tip (94% span) HTC distribution predicted by CFD and experiment data measured by Anto et al. [26] (Mexit = 0.85, 1% tip gap)

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Fig. 5

CFD and experiment tip HTC distribution at Mexit = 0.85 with 1% tip gap clearance

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Fig. 6

Over tip flow Mach number for Mexit = 0.85 taken at the midplane of the tip gap (CFD). Note the Mach number contour scale difference between (a) and (b).

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Fig. 7

Tip and near-tip oil-flow visualization results at Mexit = 0.85 (left, courtesy of Ref. [26]). CFD surface flow streamlines at 0.1 mm above the blade surface with a colormap of local static pressure (right).

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Fig. 8

Rotor blade loading at 94% span for Mexit = 0.85 and Mexit = 1.0 (CFD)

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Fig. 9

(a) CFD prediction of over-tip flow streamlines, (b) surface contours showing turbulent viscosity on the tip clearance half plane for Mexit = 0.85, and (c) Mexit = 1.0

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Fig. 10

CFD Mach number distribution at the tip clearance half plane for Mexit = 1.0. Note the Mach number contour scale difference between (a) and (b).

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Fig. 11

Tip surface HTC distribution for Mexit = 0.85 and Mexit = 1.0 (CFD)

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Fig. 12

Leakage flow turbulent viscosity along flow streamlines from pressure side x/Cx = 0.2, x/Cx = 0.5, and x/Cx = 0.8

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Fig. 13

Density gradient on a plane across the tip gap showing overtip shocks for Mexit = 1.0 (tip surface contours of HTC)

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Fig. 14

Illustration of shock/boundary layer interaction over the blade tip surface

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Fig. 15

CFD prediction of the pressure and suction surface HTC distribution at Mexit = 0.85 and Mexit = 1.0

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Fig. 16

Streamwise HTC distribution at 94% span for Mexit = 0.85 and Mexit = 1.0 (CFD)

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Fig. 17

Pressure surface spanwise distribution of turbulent viscosity and HTC at x/Cx = 0.2, x/Cx = 0.5, x/Cx = 0.8 for Mexit = 0.85 (CFD)

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Fig. 18

Pressure surface spanwise distribution of turbulent viscosity and HTC at x/Cx = 0.2, x/Cx = 0.5, x/Cx = 0.8 for Mexit = 1.0 (CFD)

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Fig. 19

Suction surface spanwise distribution of turbulent viscosity and HTC at x/Cx = 0.2, x/Cx = 0.5, x/Cx = 0.8 for Mexit = 0.85 (CFD)

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Fig. 20

Suction surface spanwise distribution of HTC at x/Cx = 0.2, x/Cx = 0.5, x/Cx = 0.8 for Mexit = 1.0 (CFD)

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