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TECHNICAL PAPERS

# Influence of Sweep on Axial Flow Turbine Aerodynamics at Midspan

[+] Author and Article Information
Graham Pullan

Whittle Laboratory, Department of Engineering,  University of Cambridge, United Kingdomgp10006@cam.ac.uk

Neil W. Harvey

Roll-Royce plc, Derby, United Kingdom

J. Turbomach 129(3), 591-598 (Jul 14, 2006) (8 pages) doi:10.1115/1.2472397 History: Received July 13, 2006; Revised July 14, 2006

## Abstract

Sweep, when the stacking axis of the blade is not perpendicular to the axisymmetric streamsurface in the meridional view, is often an unavoidable feature of turbine design. Although a high aspect ratio swept blade can be designed to achieve the same pressure distribution as an unswept design, this paper shows that the swept blade will inevitably have a higher profile loss. A modified Zweifel loading parameter, taking sweep into account, is first derived. If this loading coefficient is held constant, it is shown that sweep reduces the required pitch-to-chord ratio and thus increases the wetted area of the blades. Assuming fully turbulent boundary layers and a constant dissipation coefficient, the effect of sweep on profile loss is then estimated. A combination of increased blade area and a raised pressure surface velocity means that the profile loss rises with increasing sweep. The theory is then validated using experimental results from two linear cascade tests of highly loaded blade profiles of the type found in low-pressure aeroengine turbines: one cascade is unswept, the other has $45deg$ of sweep. The swept cascade is designed to perform the same duty with the same loading coefficient and pressure distribution as the unswept case. The measurements show that the simple method used to estimate the change in profile loss due to sweep is sufficiently accurate to be a useful aid in turbine design.

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## Figures

Figure 16

Suction-surface flow visualization, swept cascade (view perpendicular to suction surface at trailing edge)

Figure 17

Measured midspan cp distributions, unswept blade, 1.7×105<Recm<3.3×105

Figure 18

Measured midspan cpλ distributions, swept blade, 1.7×105<Recm<3.3×105

Figure 19

Midspan pressure distributions for both blades at the same Recm

Figure 20

Measured mixed-out profile loss at midspan

Figure 1

Definition of sweep

Figure 2

45deg swept blade designed on a streamsurface section

Figure 9

Loss and area ratio, αm2=62.8deg

Figure 10

Predicted pressure distributions, datum and swept blade

Figure 11

Schematic of datum, unswept cascade, side view

Figure 12

Schematic of swept cascade, side view

Figure 13

Swept cascade inlet, meridional (left), and inlet plane views

Figure 14

Photograph of the inlet contraction for the swept cascade

Figure 15

Measured contours of (p01−p0)∕(p01−p2), inlet plane, Δcon=0.01, without (left) and with bleeds

Figure 3

45deg swept blade, contours of pitchwise averaged Vs, Δcon=0.05V2

Figure 4

Figure 5

Area ratio—contours of (1+tan2αm2)∕(cos2λ+tan2αm2)

Figure 6

“Vs factor”—contours of (1+sin3λcos3αm2)

Figure 7

Loss ratio—contours of  ∣ζs∣λ∕∣ζs∣λ=0

Figure 8

Measured and predicted midspan pressure distributions, datum blade

## Errata

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