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Research Papers: Fundamental Issues and Canonical Flows

Structure of Turbulent Flows Over Forward Facing Steps With Adverse Pressure Gradient

[+] Author and Article Information
Hassan Iftekhar

Department of Automotive, Mechanical and
Manufacturing Engineering,
Faculty of Engineering and Applied Science,
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,
Faculty of Engineering and Applied Science,
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 October 26, 2015; final manuscript received February 15, 2016; published online July 15, 2016. Assoc. Editor: Mark F. Tachie.

J. Fluids Eng 138(11), 111202 (Jul 15, 2016) (12 pages) Paper No: FE-15-1769; doi: 10.1115/1.4033030 History: Received October 26, 2015; Revised February 15, 2016

This paper reports an experimental study on the effects of adverse pressure gradient (APG) and Reynolds number on turbulent flows over a forward facing step (FFS) by employing three APGs and three Reynolds numbers. A particle image velocimetry (PIV) technique was used to conduct velocity measurements at several locations downstream, and the flow statistics up to 68 step heights are reported. The step height was maintained at 6 mm, and the Reynolds numbers based on the step height and freestream mean velocity were 1600, 3200, and 4800. The mean reattachment length increases with the increase in Reynolds number without the APG whereas the mean reattachment length remains constant for increasing APG. The proper orthogonal decomposition (POD) results confirmed that higher Reynolds numbers caused the large-scale structures to be more defined and organized close to the step surface.

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References

Figures

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Fig. 1

Schematic of the mean flow features over a FFS [14,15]

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Fig. 2

Schematic of sectional a side view of test section and approximate locations of the measurement plane

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Fig. 3

Profiles of streamwise mean velocities U at selected locations normalized by Um

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Fig. 4

Profiles of wall-normal mean velocities V normalized by Um

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Fig. 5

Profiles of streamwise Reynolds normal stresses 〈uu〉 normalized by Um

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Fig. 6

Profiles of wall-normal Reynolds normal stresses 〈vv〉 normalized by Um

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Fig. 7

Profiles of Reynolds shear stresses −〈uv〉 normalized by Um

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Fig. 8

Profiles of streamwise triple velocity products normalized by Um

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Fig. 9

Profiles of wall-normal triple velocity products normalized by Um

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Fig. 10

(a) Energy fraction for N samples for APG-0, Reh = 4800, plane: P1 and (b) cumulative energy fraction for APG-0 & APG-4 for Reh = 4800 in planes P1 and P3

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Fig. 11

Isocontours corresponding to streamwise POD modes φu in the region: 0 < x/h < 8, (a), (c), (e), (g) APG-0; Reh = 1600; (b), (d), (f), (h) APG-0; Reh = 4800

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Fig. 12

Isocontours corresponding to wall-normal POD modes φv in the region: 0 < x/h < 8, (a), (c), (e), (g) APG-0; Reh = 1600; (b), (d), (f), (h) APG-0; Reh = 4800

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Fig. 13

Downstream POD modes φv of planes P1, P3, P5 in the region 0 < x/h < 66

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