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Research Papers: Flows in Complex Systems

Particle Image Velocimetry Investigation of the Coherent Structures in a Leading-Edge Slat Flow

[+] Author and Article Information
Patrick R. Richard

Department of Mechanical Engineering,
University of New Brunswick,
Fredericton, NB E3B 5A3, Canada
e-mail: patrichard44@gmail.com

Stephen John Wilkins

Department of Mechanical Engineering,
University of New Brunswick,
Fredericton, NB E3B 5A3, Canada
e-mail: Stephen_John.Wilkins@unb.ca

Joseph W. Hall

Mem. ASME
Department of Mechanical Engineering,
University of New Brunswick,
Fredericton, NB E3B 5A3, Canada
e-mail: jwhall@unb.ca

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received June 15, 2017; final manuscript received September 21, 2017; published online December 4, 2017. Assoc. Editor: Hui Hu.

J. Fluids Eng 140(4), 041105 (Dec 04, 2017) (11 pages) Paper No: FE-17-1354; doi: 10.1115/1.4038091 History: Received June 15, 2017; Revised September 21, 2017

Air traffic volume is expected to triple in the U.S. and Europe by 2025, and as a result, the aerospace industry is facing stricter noise regulations. Apart from the engines, one of the significant contributors of aircraft noise is the deployment of high-lift devices, like leading-edge slats. The unsteady turbulent flow over a leading-edge slat is studied herein. In particular, particle image velocimetry (PIV) measurements were performed on a scale-model wing equipped with a leading-edge slat in the H.J. Irving–J.C.C. Picot Wind Tunnel. Two Reynolds numbers based on wing chord were studied: Re = 6 × 105 and 1.3 × 106. A snapshot proper orthogonal decomposition (POD) analysis indicated that differences in the time-averaged statistics between the two Reynolds numbers were tied to differences in the coherent structures formed in the slat cove shear layer. In particular, the lower Reynolds number flow seemed to be dominated by a large-scale vortex formed in the slat cove that was related to the unsteady flapping and subsequent impingement of the shear layer onto the underside of the slat. A train of smaller, more regular vortices was detected for the larger Reynolds number case, which seemed to cause the shear layer to be less curved and impinge closer to the tail of the slat than for the lower Reynolds number case. The smaller structures are consistent with Rossiter modes being excited within the slat cove. The impingement of the shear layers on and the proximity of the vortices to the slat and the main wing are expected to be strong acoustic dipoles in both cases.

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Figures

Grahic Jump Location
Fig. 1

Wing and slat configuration and laser setup

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Fig. 2

Surface plots of (a) U/U∞, (b) U/U∞, (c) V/U∞, and (d) V/U∞. Vectors denote both U and V components of the mean velocity field: Re=6×105; Re=1.3×106.

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Fig. 3

Turbulent kinetic energy (TKE) (<uu>+<vv>)/2 normalized by U∞2: Re=6×105; Re=1.3×106

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Fig. 4

Energy distribution and cumulative energy for the first 30 POD eigenmodes: Re=6×105; Re=1.3×106

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Fig. 5

Streamwise component of first four POD eigenmodes, Φ, for Re=6×105 (a) first mode, (b) second mode, (c) third mode, and (d) fourth mode

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Fig. 6

Streamwise component of first four POD eigenmodes, Φ, for Re=1.3×106: (a) first mode, (b) second mode, (c) third mode, and (d) fourth mode

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Fig. 7

Instantaneous streamwise fluctuating velocity reconstructions for Re=6.5×105: (a) actual, (b) 10 POD modes, and (c) 20 POD modes

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Fig. 8

Instantaneous streamwise fluctuating velocity reconstructions for Re=1.3×106: (a) actual, (b) 10 POD modes, and (c) 20 POD modes

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Fig. 9

Random instantaneous velocity reconstructions using 10 POD modes normalized By U∞ for Re=6×105. Vectors denote U and V components of velocity.

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Fig. 10

Random instantaneous velocity reconstructions of both scalar components at the same instant using 10 POD modes normalized By U∞ for Re=1.3×106. Vectors denote U and V components of velocity.

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Fig. 11

Basic diagram showing structures and shear-layer for (a) Re = 6 × 105 and (b) Re = 1.3 × 106

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