Research Papers: Gas Turbines: Aircraft Engine

Fan–Intake Interaction Under High Incidence

[+] Author and Article Information
Teng Cao

Department of Engineering,
University of Cambridge,
Cambridge CB2 1PZ, UK
e-mail: tc367@cam.ac.uk

Nagabhushana Rao Vadlamani, Paul G. Tucker

Department of Engineering,
University of Cambridge,
Cambridge CB2 1PZ, UK

Angus R. Smith, Michal Slaby, Christopher T. J. Sheaf

Civil Installation Aerodynamics,
Rolls-Royce Plc,
Derby DE24 8BJ, UK

Contributed by the Aircraft Engine Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 14, 2016; final manuscript received August 19, 2016; published online November 2, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(4), 041204 (Nov 02, 2016) (10 pages) Paper No: GTP-16-1336; doi: 10.1115/1.4034701 History: Received July 14, 2016; Revised August 19, 2016

In this paper, we present an extensive numerical study on the interaction between the downstream fan and the flow separating over an intake under high incidence. The objectives of this investigation are twofold: (a) to gain qualitative insight into the mechanism of fan–intake interaction and (b) to quantitatively examine the effect of the proximity of the fan on the inlet distortion. The fan proximity is altered using the key design parameter, L/D, where D is the diameter of the intake, and L is the distance of the fan from the intake lip. Both steady and unsteady Reynolds-averaged numerical simulations (RANS) were carried out. For the steady calculations, a low-order fan model has been used, while a full 3D geometry has been used for the unsteady RANS. The numerical methodology is also thoroughly validated against the measurements for the intake-only and fan-only configurations on a high bypass ratio turbofan intake and fan, respectively. To systematically study the effect of fan on the intake separation and explore the design criteria, a simplified intake–fan configuration has been considered. In this fan–intake model, the proximity of the fan to the intake separation (L/D) can be conveniently altered without affecting other parameters. The key results indicate that, depending on L/D, the fan has either suppressed the level of the postseparation distortion or increased the separation-free operating range. At the lowest L/D (∼0.17), around a 5 deg increase in the separation-free angle of incidence was achieved. This delay in the separation-free angle of incidence decreased with increasing L/D. At the largest L/D (∼0.44), the fan was effective in suppressing the postseparation distortion rather than entirely eliminating the separation. Isentropic Mach number distribution over the intake lip for different L/D's revealed that the fan accelerates the flow near the casing upstream of the fan face, thereby decreasing the distortion level in the immediate vicinity. However, this acceleration effect decayed rapidly with increasing upstream distance from the fan-face.

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Fig. 1

Schematic showing the flow physics around an intake operating under a typical off-design high-incidence condition

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Fig. 2

Configuration considered for: (a) RANS on intake-only and intake-BFM, (b) unsteady RANS with full fan representation, and (c) RANS on model intake

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Fig. 3

(a) Hybrid meshing strategy: structured hexahedral elements around the intake lips, spinner and body force regions and unstructured tetrahedral meshing in the freestream and (b) computational domain with the imposed boundary conditions

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Fig. 4

Variation of (a) isentropic Mach number profiles over the intake lip pre- and post-separation and (b) distortion coefficient with increasing incidence for the intake-only case (error bars correspond to the potentiometer accuracy within ±0.2 deg)

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Fig. 5

(a) Sector mesh used for the body force simulations; comparison of (b) fan characteristic and (c) radial distribution of mass flux predicted by BFM against the RANS with full fan representation

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Fig. 6

(a) Axial variation of isentropic Mach number post separation and (b) variation of distortion coefficient with increasing incidence for configurations A and B (inset plots show the contours of stagnation pressure at the fan-face)

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Fig. 7

Sketch of model intake–fan configuration

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Fig. 8

Isentropic Mach number distribution (left) and according absolute Mach number contour (right) over the model intake-only configuration

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Fig. 9

DC60 values evaluated at the fixed location (a) and total pressure contours under the largest incidence condition (b) for intake-only and intake–fan with different L/D configurations at inlet condition 1

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Fig. 10

DC60 values evaluated at the fan-face location (a) and total pressure contours under the largest incidence condition (b) for intake-only and intake–fan with different L/D configurations at inlet condition 1 and (c) relative reduction of DC60 at fan-face under largest incidence condition for different L/D cases

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Fig. 11

DC60 values evaluated at (a) the fixed location and (b) the fan–fan location with different L/D configurations at inlet condition 2, (c) relative reduction of DC60 at fan-face under largest incidence condition for different L/D cases

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Fig. 12

(a) Isentropic Mach number distributions around the model intake lip for intake-only and intake–fan configurations prior to flow separation (αsep − 1 deg), (b) contours of isentropic Mach number on the plane locates at fan-face location (L/D = 0.24) for both intake-only and intake–fan configuration, and (c) radial distribution of the normalized mass-flux extracted at the dashed lines marked in (b)



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