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TECHNICAL PAPERS

PIV Measurements in Square Backward-Facing Step

[+] Author and Article Information
Mika Piirto, Aku Karvinen, Hannu Ahlstedt, Pentti Saarenrinne, Reijo Karvinen

Institute of Energy and Process Engineering,  Tampere University of Technology, P.O. Box 589, FI-33101 Tampere, Finland

J. Fluids Eng 129(8), 984-990 (Feb 21, 2007) (7 pages) doi:10.1115/1.2746896 History: Received October 20, 2005; Revised February 21, 2007

Measurements with both two-dimensional (2D) two-component and three-component stereo particle image velocimetry (PIV) and computation in 2D and three-dimensional (3D) using Reynolds stress turbulence model with commercial code are carried out in a square duct backward-facing step (BFS) in a turbulent water flow at three Reynolds numbers of about 12,000, 21,000, and 55,000 based on the step height h and the inlet streamwise maximum mean velocity U0. The reattachment locations measured at a distance of Δy=0.0322h from the wall are 5.3h, 5.6h, and 5.7h, respectively. The inlet flow condition is fully developed duct flow before the step change with the expansion ratio of 1.2. PIV results show that the mean velocity, root mean square (rms) velocity profiles, and Reynolds shear stress profiles in all the experimental flow cases are almost identical in the separated shear-layer region when they are nondimensionalized by U0. The sidewall effect of the square BFS flow is analyzed by comparing the experimental statistics with direct numerical simulation (DNS) and Reynolds stress model (RSM) data. For this purpose, the simulation is carried out for both 2D BFS and for square BFS having the same geometry in the 3D case as the experimental case at the lowest Reynolds number. A clear difference is observed in rms and Reynolds shear stress profiles between square BFS experimental results and DNS results in 2D channel in the spanwise direction. The spanwise rms velocity difference is about 30%, with experimental tests showing higher values than DNS, while in contrast, turbulence intensities in streamwise and vertical directions show slightly lower values than DNS. However, with the modeling, the turbulence statistical differences between 2D and 3D RSM cases are very modest. The square BFS indicates 0.5h1.5h smaller reattachment distances than the reattachment lengths of 2D flow cases.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Square BFS configuration and measurement locations. All measurements were performed in symmetry plane. Step height h=10mm.

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Figure 2

Fitting of Spalding’s velocity profile to PIV mean velocity profile in flow Case A. Spalding and log-law parameters are κ=0.41 and C=5.0.

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Figure 3

Inlet mean velocity profiles for PIV Case A, DNS of Ref. 25, DNS of Ref. 8, and RSM 2D and RSM 3D at x∕h=−3. Boundary layer thickness in DNS of Ref. 8δ99=1.2h.

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Figure 4

Inlet streamwise rms velocity profiles for PIV Case A, DNS of Ref. 25, DNS of Ref. 8, and RSM 2D and RSM 3D at x∕h=−3. Boundary layer thickness in DNS of Ref. 8δ99=1.2h. Legend see Fig. 3.

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Figure 8

Vertical rms velocity profiles for PIV cases, DNS of Ref. 8, RSM 2D and RSM 3D at x∕h=1, x∕h=4, and x∕h=10. Legend see Fig. 6.

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Figure 9

Reynolds shear stress profiles for PIV cases, DNS of Ref. 8, and RSM 2D and RSM 3D at x∕h=1, x∕h=4, and x∕h=10. Legend see Fig. 6.

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Figure 10

Spanwise rms velocity profiles for PIV cases, DNS of Ref. 8, and RSM 2D and RSM 3D at x∕h=4. Legend see Fig. 6.

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Figure 11

Streamwise rms velocity maxima at x∕h=4 with PIV test data sets of different spatial sampling resolutions

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Figure 12

Reynolds shear stress maxima at x∕h=4 with PIV test data sets of different spatial sampling resolutions. Legend see Fig. 1.

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Figure 7

Streamwise rms velocity profiles for PIV cases, DNS of Ref. 8, and RSM 2D and RSM 3D at x∕h=1, x∕h=4, and x∕h=10. Legend see Fig. 6.

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Figure 6

Mean velocity profiles for PIV cases, DNS of Ref. 8, RSM 2D, and RSM 3D at x∕h=1, x∕h=4, and x∕h=10

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Figure 5

Streamwise mean velocity and reattachment points with highest spatial sampling resolution Δy=0.0322h, which is also distance from wall

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