Research Papers

Aerodynamic Performance of a Coolant Flow Off-Take Downstream of an Outlet Guide Vane

[+] Author and Article Information
A. D. Walker

Department of Aeronautical
and Automotive Engineering
Loughborough University, United Kingdom

Rolls-Royce plc
Derby, United Kingdom

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Turbomachinery. Manuscript received July 11, 2011; final manuscript received August 2, 2011; published online October 18, 2012. Editor: David Wisler.

J. Turbomach 135(1), 011006 (Oct 18, 2012) (11 pages) Paper No: TURBO-11-1115; doi: 10.1115/1.4006332 History: Received July 11, 2011; Revised August 02, 2011

Within the compression system of a gas turbine engine a significant amount of air is removed to fulfill various requirements associated with cooling, ventilation, and sealing. Flow is usually removed through off-takes located in regions where space is restricted, while the flow is highly complex containing blade wakes, secondary flows, and other flow features. This paper investigates the performance of a pitot style off-take aimed at providing a high pressure recovery in a relatively short length. For this to be achieved some prediffusion of the flow is required upstream of the off-take (i.e., by making the off-take larger than the captured streamtube). Although applicable to a variety of applications, the system is targeted at an intercooled aero-engine concept where the off-take would be located aft of the fan outlet guide vane (OGV) root and provide coolant flow to the heat exchangers. Measurements and numerical predictions are initially presented for a baseline configuration with no off-take present. This enabled the OGV near field region to be characterized and provided a datum, relative to which the effects of introducing an off-take could be assessed. With the off-take present a variety of configurations were investigated including different levels of prediffusion, prior to the off-take, and different off-take positions. For very compact systems of short length, such that the gap between the OGV and off-take is relatively small, the amount of prediffusion achievable is limited by the off-take pressure field and its impact on the upstream OGV row. This pressure field is also influenced by parameters such as the nondimensional off-take height and splitter thickness. The paper analyses the relative importance of these various effects in order to provide some preliminary design rules. For systems of increased length a significant amount of flow prediffusion can be achieved with little performance penalty. However, the prediffusion level is eventually limited by the increased distortion and pressure losses associated with the captured streamtube.

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Fig. 1

NEWAC schematic of intercooled engine [8]

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Fig. 2

Off-take concept schematic

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Fig. 3

Test rig configurations: (a) parallel duct and (b) with off-take

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Fig. 4

Normalized axial velocity contours at OGV exit with varying blade hub gaps

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Fig. 5

CFD total pressure contours at FOGV exit

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Fig. 6

OGV exit capture streamtube comparison

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Fig. 7

Normalized axial velocity contours at various downstream planes

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Fig. 8

Kinetic energy flux static pressure coefficient

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Fig. 9

Circumferentially averaged normalized velocity profiles at axial locations through duct

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Fig. 10

Whole plane pressure losses through system: (a) BHG 0.42% span and (b) no BHG

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Fig. 11

Pressure loss development for various mass flows through datum duct

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Fig. 12

Visualization of predicted capture streamtube and constant outer radius approximation

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Fig. 13

OGV exit static pressure variation with off-take proximity (PR1.16)

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Fig. 14

OGV exit static pressure variation with prediffusion (X/C = 0.49)

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Fig. 15

Comparison of CFD predictions

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Fig. 16

Potential flow model

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Fig. 17

Off-take location design envelope based on inner wall static pressure (Cp = 20%)

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Fig. 18

Off-take location design envelope based on stagnation streamline static pressure (Cp = 20%)

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Fig. 19

Shear and pressure force comparison (X/C = 0.73)

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Fig. 20

Throat plane kinetic energy coefficient

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Fig. 21

Throat plane total pressure losses

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Fig. 22

Throat plane total pressure losses




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