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Research Papers

Effect of Roughness and Unsteadiness on the Performance of a New Low Pressure Turbine Blade at Low Reynolds Numbers

[+] Author and Article Information
Francesco Montomoli, Howard Hodson

Whittle Laboratory, University of Cambridge, Cambridge, CB3 0DY, UK

Frank Haselbach

 Rolls-Royce plc., Derby, DE24 8BJ, UK

J. Turbomach 132(3), 031018 (Apr 05, 2010) (9 pages) doi:10.1115/1.3148475 History: Received September 11, 2008; Revised February 15, 2009; Published April 05, 2010; Online April 05, 2010

This paper presents a study of the performance of a high-lift profile for low pressure turbines at Reynolds numbers lower than in previous investigations. By following the results of Coull (2008, “Velocity Distributions for Low Pressure Turbines,” ASME Paper No. GT2008-50589) on the design of high-lift airfoils, the profile is forward loaded. The separate and combined effects of roughness and wake passing are compared. On a front loaded blade, the effect of incidence becomes more important and the consequences in terms of cascade losses, is evaluated. The experimental investigation was carried out in the high speed wind tunnel of Whittle Laboratory, University of Cambridge. This is a closed-circuit continuous wind tunnel where the Reynolds number and Mach number can be fixed independently. The unsteadiness caused by wake passing in front of the blades is reproduced using a wake generator with rotating bars. The results confirm that the beneficial effect of unsteadiness on losses is present even at the lowest Reynolds number examined (Re3=20,000). This beneficial effect is reduced at positive incidence. With a front loaded airfoil and positive incidence, the transition occurs on the suction side close to the leading edge and this results in higher losses. This has been found valid for the entire Reynolds range investigated (20,000Re3140,000). Roughening the surface also had a beneficial effect on the losses but this effect vanishes at the lower Reynolds numbers, i.e., (Re330,000), where the surface becomes hydraulically smooth. The present study suggests that a blade with as-cast surface roughness has a lower loss than a polished one.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

View of high speed wind tunnel: (left) cross section; (right) photograph taken looking toward the inlet

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Figure 2

H2 airfoil schematic

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Figure 3

H2 roughness compared to Vera (9)

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Figure 4

Isentropic Mach number distribution on H2, MISES calculations, Re3=30,000

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Figure 5

KSI for steady and unsteady inflows, i=0 deg, Ra=5 μm

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Figure 6

Ensemble average velocity magnitude on the suction side from 45% S0 to 95% S0, Re=30.000, i=0 deg, g=21 mm, unsteady inflow

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Figure 7

(Left) s-t diagram of TKE thickness; (Right) θ and H12 at trailing edge, Re=30.000, i=0 deg, g=21 mm, Ra=5 μm, unsteady inflow

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Figure 8

KSI for steady and unsteady inflows, i=0 deg, Ra=5,1 μm

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Figure 9

KSI for steady inflow, i=0/+7 deg, Ra=5 μm

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Figure 10

KSI for steady and unsteady conditions, i=0/+7 deg, Ra=5 μm

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Figure 11

KSI for steady and unsteady conditions, i=0/+7 deg, Ra=5 μm, g=21/24 mm

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