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Article

Effects of Elevated Free-Stream Turbulence on Actively Controlled Separation Bubble

[+] Author and Article Information
E. Halfon, B. Nishri, A. Seifert, I. Wygnanski

Department of Fluid Mechanics and Heat Transfer, Faculty of Engineering, Tel-Aviv University, Israel

J. Fluids Eng 126(6), 1015-1024 (Mar 11, 2005) (10 pages) doi:10.1115/1.1839933 History: Received July 15, 2002; Revised April 15, 2004; Online March 11, 2005
Copyright © 2004 by ASME
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References

Figures

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The effect of FST level on the phase of the velocity cross spectral density at the excitation frequency. Data taken at maximum amplitude location [x=70 mm for F=25 Hz, (a) and x=40 mm for F=80 Hz, (b)] and just upstream of the LE (x=−2 mm)
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(a) Top view of the experimental set-up. All dimensions in mm. (b) Side view of the experimental set-up. (c) A typical cell of the turbulence generating gri
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The effect of grid position on normalized turbulence levels, measured 100 mm upstream of the plate LE. M=25 mm, rectangular grid and bars. Here x is the distance between the grid and the measurement location
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The effect of grid position (determining the FST level) on FST turbulence spectra, measured 100 mm upstream of the plate LE. M=25 mm, rectangular grid, rectangular bars. Data was acquired at z=0 and y=100 mm
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(a) The effect of grid position (determining FST level) on turbulent scales using two wire correlations. Note that the initial spanwise separation between the hot-wire centers was about 3 mm while each HW was about 2 mm wide. (b) The effect of grid position (determining FST level) on streamwise turbulent scales
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The effect of elevated FST on velocity spectra inside the separated shear layer close to the plate LE (x=10 mm). Ue is the local free stream velocity
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The effect of FST level on mean wall pressures. No AFC
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The effect of FST level on Y1/2 (the wall normal direction in which the local mean velocity is half the external velocity). No AFC
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The reattachment distance, based on the inflection point in the Cp distributions for the baseline and for the controlled bubbles
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(a) The effect of FST level on H (the boundary layer shape factor) downstream of reattachment. (b) The effect of FST level on θ (the boundary layer momentum thickness) downstream of reattachment
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(a) The effect of FST level on uncontrolled (no AFC) mean wall Cpdeviations from the Cp of FST=0.4% (of Fig. 4) when the flow was uncontrolled. (b) The effect of FST level on controlled (AFC activated) mean wall Cpdeviations from the uncontrolled Cp (of Fig. 4) when the flow was excited at F+≈1 (F=25 Hz). (c) The effect of FST level on controlled (AFC activated) mean wall Cpdeviations from the uncontrolled Cp (of Fig. 4) when the flow was excited at F+≈3 (F=80 Hz)
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(a) The effect of FST level on uncontrolled (no AFC) Y1/2 (referenced) to the Y1/2 of the Tu=0.4% data (of Fig. 7). (b) The effect of FST level on controlled (AFC activated) Y1/2deviations from the uncontrolled Y1/2 (shown in Fig. 7) using F+≈1 (25 Hz). (c) The effect of FST level on controlled (using F=80 Hz)Y1/2deviations from the uncontrolled Y1/2 (of Fig. 7) using F+≈3 (80 Hz)
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The effect of periodic excitation on the boundary layer shape factor downstream of reattachment at two FST levels: (a) FST=0.4%, (b) FST=11%
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The effect of FST level on oscillating x momentum integrated across the shear layer at the fundamental excitation frequency (a) and its harmonic (b), using F+≈1 (25 Hz) and F+≈3 (80 Hz)

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