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Research Papers: Flows in Complex Systems

Turbulent Flows Over Forward Facing Steps With Surface Roughness

[+] Author and Article Information
Weijie Shao

Department of Automotive, Mechanical and
Manufacturing Engineering,
University of Ontario Institute of Technology,
2000 Simcoe Street North,
Oshawa, ON L1H 7K4, Canada

Martin Agelin-Chaab

Department of Automotive, Mechanical and
Manufacturing Engineering,
University of Ontario Institute of Technology,
2000 Simcoe Street North,
Oshawa, ON L1H 7K4, Canada
e-mail: martin.agelin-chaab@uoit.ca

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received November 3, 2014; final manuscript received June 25, 2015; published online September 3, 2015. Assoc. Editor: Mark F. Tachie.

J. Fluids Eng 138(2), 021103 (Sep 03, 2015) (12 pages) Paper No: FE-14-1636; doi: 10.1115/1.4031258 History: Received November 03, 2014; Revised June 25, 2015

This paper reports an investigation of the effects of surface conditions of forward-facing steps (FFS) on turbulent flows. Three surface conditions including one smooth step and two rough step surfaces created using sandpapers were studied. A particle image velocimetry (PIV) technique was used to conduct velocity measurements at several locations downstream, and the statistics up to 60 step heights are reported. The step height was maintained at 6 mm, and three Reynolds numbers of Reh = 1600, 3200, and 4800, where Reh is based on the step height and freestream mean velocity, were studied. The results indicate that the reattachment length of a FFS increases with Reynolds number but decreases with increasing surface roughness. The proper orthogonal decomposition (POD) results showed the step roughness affects even the large-scale structures.

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Figures

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Fig. 1

A sketch of the mean flow pattern over a FFS [4]

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Fig. 2

Schematic of a sectional side view of the test section indicating the coordinate axes, the channel heights, trips, and measurement planes (P0 to P5)

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Fig. 3

Profiles of normalized streamwise mean velocities, U/Um, for SM, SP-24, and SP-36 at x/h = 4, 10, 40, and 60. All symbols are as in (a).

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Fig. 4

Profiles of normalized wall-normal mean velocities, V/Um, for SM, SP-24, and SP-36 at x/h = 4, 10, 40, and 60. All symbols are as in (a).

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Fig. 5

Profiles of normalized streamwise Reynolds normal stresses, 〈uu〉/Um2, for SM, SP-24, and SP-36 at x/h = 4, 10, 40, and 60. All symbols are as in (a).

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Fig. 6

Profiles of normalized wall-normal Reynolds normal stresses, 〈vv〉/Um2, for SM, SP-24, and SP-36 at x/h = 4, 10, 40, and 60. All symbols are as in (a).

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Fig. 7

Profiles of normalized Reynolds shear stresses, − 〈uv〉/Um2, for SM, SP-24, and SP-36 at x/h = 4, 10, 40, and 60. All symbols are as in (a).

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Fig. 8

Profiles of normalized production of streamwise Reynolds normal stresses, P*uu = Puu × h/Um3, for SM, SP-24, and SP-36 at x/h = 4, 10, 40, and 60. All symbols are as in (a).

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Fig. 9

Profiles of normalized production of wall-normal Reynolds normal stresses, P*vv = Pvv × h/Um3, for SM, SP-24, and SP-36 at x/h = 4, 10, 40, and 60. All symbols are as in (a).

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Fig. 10

Profiles of normalized production of Reynolds shear stresses, P*uv = Puv × h/Um3, for SM, SP-24, and SP-36 at x/h = 4, 10, 40, and 60. All symbols are as in (a).

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Fig. 11

Profiles of 〈u3+ uv2〉/Um3 for SM, SP-24, and SP-36 at x/h = 4, 10, 40, and 60. All symbols are as in (a).

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Fig. 12

Profiles of 〈u2v + v3〉/Um3 over SM, SP-24, and SP-36 for SM, SP-24, and SP-36 at x/h = 4, 10, 40, and 60. All symbols are as in (a).

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Fig. 13

Streamline patterns of POD mode-shapes (φu) and contours corresponding to streamwise POD modes in the region: 0 ≤ x/h ≤ 8. Note: (a), (c), (e), and (g) are for the smooth step (SM); (b), (d), (f), and (h) are for the rough step (SP-24). (a) Mode 1, (b) mode 1, (c) mode 5, (d) mode 5, (e) mode 10, (f) mode 10, (g) mode 4000, and (h) mode 4000.

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Fig. 14

Streamline patterns of POD mode-shapes (φv) and contours corresponding to wall-normal POD modes in the region: 0 ≤ x/h ≤ 8. Note: (a), (c), (e), and (g) are for the smooth step (SM); (b), (d), (f), and (h) are for the rough step (SP-24). (a) Mode 1, (b) mode 1, (c) mode 5, (d) mode 5, (e) mode 10, (f) mode 10, (g) mode 4000, and (h) mode 4000.

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