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Research Papers: Flows in Complex Systems

Two-Dimensional Experimental Investigation on the Effects of a Fowler Flap Gap and Overlap Size on the Wake Flow Field

[+] Author and Article Information
David Demel, Mohsen Ferchichi, William D. E. Allan, Marouen Dghim

Department of Mechanical and
Aerospace Engineering,
Royal Military College of Canada,
Kingston, ON K7K 7B4, Canada

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received September 27, 2015; final manuscript received July 4, 2016; published online November 3, 2016. Editor: Malcolm J. Andrews.This work was prepared while under employment by the Government of Canada as part of the official duties of the authors, and as such the copyright is owned by that Government, which reserves its own copyright under national law.

J. Fluids Eng 139(2), 021101 (Nov 03, 2016) (12 pages) Paper No: FE-15-1694; doi: 10.1115/1.4034524 History: Received September 27, 2015; Revised July 04, 2016

This work details an experimental investigation on the effects of the variation of flap gap and overlap sizes on the flow field in the wake of a wing-section equipped with a trailing edge Fowler flap. The airfoil was based on the NACA 0014-1.10 40/1.051 profile, and the flap was deployed with 40 deg deflection angle. Two-dimensional (2D) particle image velocimetry (PIV) measurements of the flow field in the vicinity of the main wing trailing edge and the flap region were performed for the optimal flap gap and overlap, as well as for flap gap and overlap increases of 2% and 4% chord beyond optimal, at angles of attack of 0 deg, 10 deg, and 12 deg. For all the configurations investigated, the flow over the flap was found to be fully stalled. At zero angle of attack, increasing the flap gap size was found to have minor effects on the flow field but increased flap overlap resulted in misalignment between the main wing boundary layer (BL) flow and the slot flow that forced the flow in the trailing edge region of the main wing to separate. When the angle of attack was increased to near stall conditions (at angle of attack of 12 deg), increasing the flap gap was found to energize and improve the flow in the trailing edge region of the main wing, whereas increased flap overlap further promoted flow separation on the main wing suction surface possibly steering the wing into stall.

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Figures

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Fig. 1

Fowler flap gap (G) and overlap (O)

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Fig. 2

Experimental setup. Test section (a) PIV measurements domain (b).

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Fig. 3

BL development on the upper surface of the wing trailing edge in the clean configuration. Mean streamwise velocity (a) TKE (b) in local coordinate system (x,y).

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Fig. 4

BL development on the upper surface of the wing trailing edge in the baseline configuration (G0–O0). Mean streamwise velocity (a) TKE (b) in local coordinate system (x,y).

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Fig. 5

BL development on the upper surface of the wing trailing edge for increased flap gap configuration (G4–O0). Mean streamwise velocity (a) TKE (b) in local coordinate system (x,y).

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Fig. 6

BL development on the upper surface of the wing trailing edge for increased flap overlap configuration (G0–O4). Mean streamwise velocity (a) TKE (b).

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Fig. 7

Flow streamlines: G0–O0 (a), G4–O0 (b), and G0–O4 (c)

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Fig. 8

Flap upper surface pressure coefficient

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Fig. 9

Wake mean velocity profiles progression with increasing gap (a) TKE (b) in (X,Y). (○) G0–O0; (△) increase of 0.02Cw; (□) increase of 0.04Cw.

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Fig. 10

Wake mean velocity profiles progression with increasing overlap (a) TKE (b) in (X,Y). (○) G0–O0; (△) increase of 0.02Cw; (□) increase of 0.04Cw.

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Fig. 11

Slot flow in G0–O0 configuration. Mean slot velocity magnitude (with direction) (a) and TKE (b) in the wake in local similarity coordinates.

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Fig. 12

Slot flow in G4–O0 configuration. Mean slot velocity magnitude (with direction) (a) and TKE (b) in the wake in local similarity coordinates.

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Fig. 13

Slot flow in G0–O4 configuration. Mean slot velocity magnitude (with direction) (a) and TKE (b) in the wake in local similarity coordinates.

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Fig. 14

Normalized mean spanwise vorticity in the wake. G0–O0 (a), G4–O0 (b), and G0–O4 (c).

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Fig. 15

Relative flow inclination angle progression. Configuration G0–O0 (○,•) configuration G4–O0 (□,▪), and configuration G0–O4 (△,▲). BL flow (empty symbols), slot flow (solid symbols). Solid line: direction of chordline.

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Fig. 16

Effect of angle of attack in the clean configuration. Boundary layer flow at X/Cw = −0.025 (a), Streamlines at α = 12 deg (b).

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Fig. 17

Flow streamlines at α = 12 deg: G0–O0 (a), G4–O0 (b), and G0–O4 (c)

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