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Research Papers: Fundamental Issues and Canonical Flows

Measurements of the Effects of Streamwise Riblets on Boundary Layer Turbulence

[+] Author and Article Information
Derek B. Ancrum

Department of Mechanical and
Aerospace Engineering,
Carleton University,
Ottawa, ON K1S 5B6, Canada

Metin I. Yaras

Professor
Department of Mechanical and
Aerospace Engineering,
Carleton University,
Ottawa, ON K1S 5B6, Canada
e-mail: Metin.Yaras@carleton.ca

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received September 9, 2016; final manuscript received May 10, 2017; published online August 11, 2017. Assoc. Editor: Daniel Maynes.

J. Fluids Eng 139(11), 111203 (Aug 11, 2017) (10 pages) Paper No: FE-16-1591; doi: 10.1115/1.4037044 History: Received September 09, 2016; Revised May 10, 2017

This study presents experimental results on the effects of riblets on the coherent structures of turbulence within a turbulent spot. The riblet spacings of the study correspond to 0.5 and 1.5 times the natural spacing of the low-speed streak. The cross-sectional dimensions of the riblets were chosen to control the spatial distribution of wave packets consisting of streamwise-aligned hairpin vortices. Both riblet spacings demonstrated effective control on the spanwise positioning of the wave packets. The wider-spaced riblets reduced spanwise mutual interaction between wave packets. The closer-spaced riblets promoted this interaction via spanwise-oriented vortical structures which produced stronger turbulent fluctuations.

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References

Figures

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Fig. 1

Schematic of a hairpin vortex

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Fig. 2

Schematic of secondary flows within streamwise grooves of a closely spaced-riblet surface driven by the interaction of the hairpin-vortex legs with the riblets

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Fig. 3

Formation of vortices spanning multiple riblet grooves through K–H instability

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Fig. 4

Test section configuration

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Fig. 6

Undisturbed boundary layer velocity profiles for ReL = 3.1 × 105 ((a), (c), and (e)) and ReL = 2.2 × 105 ((b), (d), and (f)). For the riblet surfaces, the dashed horizontal line identifies the location of the riblet tip.

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Fig. 7

Perturbation velocity in the z–t plane on the smooth surface measured at x = 600 mm for (a) ReL = 2.2 × 105 and (b) ReL = 3.1 × 105

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Fig. 8

Perturbation velocities in the y–z plane on the smooth surface measured at x = 600 mm for (a) ReL = 2.2 × 105 and (b) ReL = 3.1 × 105

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Fig. 9

Perturbation-velocity distribution in the y–t plane over the smooth surface measured at x = 600 mm at (a) z/δref*=0.0, (b) z/δref*=10.0, (c) z/δref*=20.0, and (d) y/δref*=30.0

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Fig. 10

Variation of the spot propagation parameter for ReL = 3.1 × 105 over the smooth surface

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Fig. 11

Comparison of the ensemble-averaged streamwise velocity and spanwise vorticity at x = 600 mm and ReL = 3.1 × 105 between the smooth surface and the (a) closer-spaced riblet; groove center, (b) closer-spaced riblet; riblet tip, (c) wider-spaced riblet; groove center, and (d) wider-spaced riblet; riblet tip

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Fig. 12

Perturbation-velocity distribution in the y–z plane: (a) smooth surface, (b) surface with closer-spaced riblets, and (c) surface with wider-spaced riblets

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Fig. 13

Schematic of a hairpin vortex and its induced motions over an isolated riblet. Regions of negative and positive perturbation velocities are shown above and adjacent to the riblet, respectively.

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Fig. 14

Topology of the turbulent spot developing over the wider-spaced-riblet surface at (a) y/δref*=8.8 and (b) y/δref*=2.3 (ReL = 3.1 × 105 and x = 600 mm)

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Fig. 15

Topology of the turbulent spot over the closer-spaced-riblet surface at (a) y/δref*=8.8 and (b) y/δref*=2.3 (ReL = 3.1 × 105 and x = 600 mm)

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Fig. 16

Perturbation velocity of the turbulent spot in the y–t plane on the closer-spaced-riblet surface (ReL = 3.1 × 105 and x = 600 mm)

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Fig. 17

Schematic of two spanwise-adjacent wave packets interacting with each other and the prevailing spanwise vortices over the surface with closer-spaced riblets

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Fig. 18

Streamwise variation of the spot propagation parameter over all three test surfaces at both flow Reynolds numbers

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