Abstract
Turbulent characteristics in wall-wake flows downstream of wall-mounted and near-wall cylinders are investigated. The distributions of the defect of streamwise velocity, Reynolds shear stress and turbulence intensities exhibit a certain degree of self-preserving characteristic when they are scaled by their respective peak defect values. For the velocity defect distributions, the vertical distances are scaled by the half-width of peak defect velocity. However, for the distributions of the defects of the Reynolds shear stress and the turbulence intensities, the vertical distances are scaled by the half-width of Reynolds shear stress defect. The peak defects of all the quantities reduce with longitudinal distance signifying the recovery of the upstream distributions of the individual quantities. The third-order correlations reveal that for the wall-mounted cylinder, a streamwise acceleration associated with a downward flux of streamwise Reynolds normal stress (SRNS) in the inner-layer of wall-wake composes sweeps and a streamwise deceleration associated with an upward flux of SRNS in the outer-layer forms ejections. On the other hand, for the near-wall cylinder, a streamwise deceleration associated with a downward flux of SRNS in the inner-layer of wall-wake flow and the gap flow produces the inward interaction events, while the outer-layer characteristic is similar to that of wall-mounted cylinder. The turbulent kinetic energy (TKE) budget in the wake flow demonstrates strong negative pressure energy diffusion in addition to a strong TKE dissipation and diffusion and that in the gap flow exhibits a minor positive peak of pressure energy diffusion and a minor negative peak of TKE diffusion.
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Abbreviations
- D :
-
Cylinder diameter (L)
- d 50 :
-
Median size of sand (L)
- E D :
-
Nondimensional TKE dissipation rate (–)
- \( \mathsf{F} \) :
-
Flow Froude number, \( \overline{U} \)/(gh)0.5 (–)
- F ii :
-
Power spectral density function (L2T−1)
- f :
-
Frequency (T−1)
- f kw :
-
Vertical flux of TKE, \( \overline{{kw^{\prime}}} \) (L3T−3)
- g :
-
Acceleration due to gravity (LT−2)
- h :
-
Flow depth (L)
- k :
-
TKE, 0.5(\( \overline{{u^{\prime}u^{\prime}}} \) + \( \overline{{v^{\prime}v^{\prime}}} \) + \( \overline{{w^{\prime}w^{\prime}}} \)) (L2T−2)
- k s :
-
Roughness height (L)
- k w :
-
Wave number (L−1)
- M jk :
-
Third-order correlations (–)
- P D :
-
Nondimensional pressure energy diffusion rate (–)
- p′:
-
Fluctuations of hydrostatic pressure relative to mass density of fluid (L2T−2)
- p D :
-
Pressure energy diffusion rate (L2T−3)
- \( \mathsf{R} \) :
-
Reynolds number characterized by cylinder diameter, \( \overline{U} \) D/υ (–)
- \( \mathsf{R}_{\text{*}} \) :
-
Shear-particle Reynolds number, u*ks/υ (–)
- S uu :
-
Spectral density as a function of kw (L3T−2)
- T D :
-
Nondimensional TKE diffusion rate (–)
- T P :
-
Nondimensional TKE production rate (–)
- t D :
-
TKE diffusion rate (L2T−3)
- t P :
-
TKE production rate (L2T−3)
- U :
-
Time-average approaching velocity at an elevation z (LT−1)
- \( \overline{U} \) :
-
Depth-averaged approaching velocity (LT−1)
- u :
-
Time-averaged streamwise velocity component (LT−1)
- u′:
-
Fluctuations of streamwise velocity (LT−1)
- u * :
-
Approaching shear velocity (LT−1)
- v :
-
Time-averaged transverse velocity component (LT−1)
- v′:
-
Fluctuations of spanwise velocity (LT−1)
- v D :
-
Viscous diffusion rate (L2T−3)
- w :
-
Time-averaged vertical velocity component (LT−1)
- w′:
-
Fluctuations of vertical velocity (LT−1)
- x :
-
Streamwise distance (L)
- y :
-
Spanwise distance (L)
- z :
-
Vertical distance (L)
- z 1 :
-
Height of occurrence of half of maximum velocity defect (L)
- z 2 :
-
Height of occurrence of half of peak RSS defect (L)
- Δu :
-
Velocity defect, U(z) − u(z) (LT−1)
- Δz :
-
Gap thickness (L)
- Δτ :
-
RSS defect relative to mass density of fluid, τ(z)|upstream − τ(z)|downstream (L2T−2)
- Δσ u :
-
Streamwise turbulence intensity defect, σu(z)|upstream − σu(z)|downstream (LT−1)
- Δσ w :
-
Vertical turbulence intensity defect, σw(z)|upstream − σw(z)|downstream (LT−1)
- ε :
-
TKE dissipation rate (L2T−3)
- ρ :
-
Mass density of fluid (ML−3)
- σ u :
-
Streamwise turbulence intensity (LT−1)
- σ w :
-
Vertical turbulence intensity (LT−1)
- τ :
-
RSS relative to mass density of fluid (L2T−2)
- υ :
-
Kinematic viscosity of fluid (L2T−1)
- m :
-
Peak value
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Dey, S., Lodh, R. & Sarkar, S. Turbulence characteristics in wall-wake flows downstream of wall-mounted and near-wall horizontal cylinders. Environ Fluid Mech 18, 891–921 (2018). https://doi.org/10.1007/s10652-018-9573-0
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DOI: https://doi.org/10.1007/s10652-018-9573-0