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Large-scale vortical structure of turbulent separation bubble affected by unsteady wake

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Abstract

The large-scale vortical structure of a turbulent separation bubble under the influence of an unsteady wake was investigated. The unsteady wake was generated by a spoked-wheel type wake generator installed in front of the separation bubble. This wake generator was rotated either clockwise or counter-clockwise at Re H=5.600. The mechanism of vortex shedding from the separation bubble was analyzed in detail by taking a conditional average as well as a phase average. Spatial box filtering (SBF) was used to extract the large-scale vortical structure from the turbulent separation bubble affected by the unsteady wake. To elucidate the influence of the unsteady wake on the large-scale vortical structure, conditional averages of the velocity, vorticity and turbulent kinetic energy were calculated. The nature of the convection of the vortical structure under the influence of an unsteady wake was analyzed. The dipole acoustic pressure level was predicted using Curle's integral of wall-pressure fluctuations.

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Abbreviations

H :

half-thickness of a blunt body (mm)

R pp :

cross-correlation of wall pressure

R pu :

cross-correlation of wall pressure and streamwise velocity

R pv :

cross-correlation of wall pressure and wall-normal velocity

R s :

distance from acoustic source point to observation point (mm)

Re H :

Reynolds number, U ∞ H/ν

St H :

normalized wake-passing frequency, f p H/U ∞

T :

vortex shedding period (s)

U ∞ :

free-stream velocity (m/s)

b :

width of test section (mm)

f p :

wake-passing frequency (Hz)

k :

turbulent kinetic energy (m2/s2)

l j :

cosine of angle

p :

instantaneous wall pressure (Pa)

p rms :

root-mean-square of wall pressure (Pa)

p SBF :

spatial-box-filtered wall pressure (Pa)

p d :

acoustic dipole source (Pa)

p w :

conditionally averaged wall pressure [Pa]

q :

dynamic pressure, 0.5ρU ∞ 2 (Pa)

r :

distance from origin to observation point (mm)

u c :

convection velocity (m/s)

x R :

time-mean reattachment length (mm)

δ ij :

Kronecker's symbol

ϕ :

phase angle (°)

λ :

wavelength (mm)

θ :

inclination angle (°)

ϑ :

angle between vertical axis and observation point (°)

ρ :

density (kg/m3)

τ :

time delay (s)

ω z :

spanwise vorticity (m2/s)

AR:

aspect ratio

CW:

clockwise

CCW:

counter-clockwise

SBF:

spatial box filtering

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Acknowlegements

This work was supported by a grant from the National Research Laboratory of the Ministry of Science and Technology, Korea.

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Authors and Affiliations

  1. Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 373-1 Kuseong-dong Yuseong-gu, 305-701, Daejeon, Korea

    S. Chun & H. J. Sung

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  1. S. Chun
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  2. H. J. Sung
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Correspondence to H. J. Sung.

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Chun, S., Sung, H.J. Large-scale vortical structure of turbulent separation bubble affected by unsteady wake. Exp Fluids 34, 572–584 (2003). https://doi.org/10.1007/s00348-003-0591-3

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