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Research Papers

A Review of Surface Roughness Effects in Gas Turbines

[+] Author and Article Information
J. P. Bons

Department of Aerospace Engineering, Ohio State University, 2300 West Case Road, Columbus, OH 43017

J. Turbomach 132(2), 021004 (Jan 11, 2010) (16 pages) doi:10.1115/1.3066315 History: Received December 13, 2007; Revised September 10, 2008; Published January 11, 2010; Online January 11, 2010

The effects of surface roughness on gas turbine performance are reviewed based on publications in the open literature over the past 60 years. Empirical roughness correlations routinely employed for drag and heat transfer estimates are summarized and found wanting. No single correlation appears to capture all of the relevant physics for both engineered and service-related (e.g., wear or environmentally induced) roughness. Roughness influences engine performance by causing earlier boundary layer transition, increased boundary layer momentum loss (i.e., thickness), and/or flow separation. Roughness effects in the compressor and turbine are dependent on Reynolds number, roughness size, and to a lesser extent Mach number. At low Re, roughness can eliminate laminar separation bubbles (thus reducing loss) while at high Re (when the boundary layer is already turbulent), roughness can thicken the boundary layer to the point of separation (thus increasing loss). In the turbine, roughness has the added effect of augmenting convective heat transfer. While this is desirable in an internal turbine coolant channel, it is clearly undesirable on the external turbine surface. Recent advances in roughness modeling for computational fluid dynamics are also reviewed. The conclusion remains that considerable research is yet necessary to fully understand the role of roughness in gas turbines.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Gas turbine roughness-related journal articles published in ASME Journal of Turbomachinery, ASME Journal of Engineering for Gas Turbines and Power, and AIAA Journal of Propulsion and Power, AIAA Journal of Aircraft, and AIAA Journal (numbers are not comprehensive prior to 1990). Also, roughness-related IGTI conference papers from 2000–2006.

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Figure 2

Deposition on first stage vane of utility gas turbine after approximately 8000 h of service. Firing temperature 1150°C.

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Figure 3

Eroded test rotor blades due to sand ingestion near design point during 9 h (Fig. 9 from Ghenaiet (20))

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Figure 4

Nikuradse’s original sand-roughened pipe flow data (Fig. 20.18 from Schlichting (39))

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Figure 5

Samples of erosion, deposition, and TBC spallation on turbine blading. (a) Erosion sample from suction surface leading edge region (7×10 mm2). (b) Fuel deposition sample from pressure surface trailing edge region (3×4 mm2). (c) Spallation on turbine blade pressure surface.

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Figure 6

Compressor cascade loss measurements for rough and smooth blades versus Rec (Fig. 8 from Leipold (70))

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Figure 7

Contours of total pressure rise coefficient at the exit of compressor stator for (a) smooth and (b) LE roughness only conditions. Rec=2.7×105 (Fig. 2 from Gbadebo (37)).

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Figure 8

Area-averaged loss coefficient versus Rec for HP vane cascade at exit Mach number=0.5 and 0.9 (Figs.  64 from Boyle and Senyitko (43)). (Recx≈0.5Rec).

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Figure 9

Vane Nu data for various Re and Tu. (Fig. 6 from Stripf (60).) (1.6 Re1≈Recx)

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Figure 10

Vane heat transfer coefficient data for various Ra at Recx=4.7×106 and Tu=9% (Fig. 1 from Bunker (93)).

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Figure 11

Turbine vane total pressure loss data from Matsuda (95) for various Rz/c for three values of Rec and Tu=0.5%. (Recx≈0.7 Rec) (Fig. 7).

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Figure 12

Turbine vane total pressure loss data from Matsuda (95) for Rec=8.7×105 and Tu=0.5%: ((a)–(d)) rough vanes with smooth endwall; (e) rough C7 vane with rough endwall. (Recx≈0.7Rec) (Figs.  915).

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Figure 13

Area-averaged film effectiveness versus blowing ratio for roughness elements upstream, downstream, or both upstream and downstream (“all”) of film holes on vane cascade. Rec=1×106(Recx≈0.5 Rec) and Tu=6% (Fig. 5 from Rutledge (99)).

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Figure 14

(a) Cutting plane showing the viscous adaptive Cartesian grid for a 240×60mm2 patch of erosion roughness. (b) Surface grid on the erosion surface showing grid refinement near leading edge. From Bons (119).

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Figure 15

Comparison of percent change in cf and St from experiment and computation (3D RANS and DEM). Two different roughness surfaces: fuel deposit and erosion. Zero pressure gradient turbulent boundary layer with Re=1×106. From Bons (119).

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Figure 16

Comparison of predicted and measured suction side heat transfer coefficient on a linear vane cascade for various roughness heights (k), turbulence levels (Tu1), and Re1. (1.6 Re1≈Recx) (Fig. 6 from Stripf (73)).

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