Spatially-averaged oscillatory flow over a rough bed

Coleman, Stephen E.; Nikora, Vladimir; Schlicke, Ted

doi:10.2478/s11600-008-0016-z

Cited by 11 publications

(23 citation statements)

References 27 publications

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“…In vertical to transverse profiles comparison, Papanicolaou and Hilldale [29] suggested that D 2 and λ 2 should be larger than D 3 and λ 3 , which is also agreed by our findings on all flows over hydraulically smooth, rough and water-worked beds. As shown in Table 2, all turbulence intensities D 1 , D 2 , D 3 , λ 1 , λ 2 and λ 3 in Figures 4-6 compare reasonably well with literature findings. Detailed comparison reveals that λ 1 is slightly higher than most proposed values.…”

Section: Turbulence Characteristicssupporting

confidence: 88%

“…This concept can create a non-moving deposited surface topography suitable to represent the natural open channel rough bed, which is usually produced in similar water-worked manner. As suggested by Coleman et al [3] after studying different forms of rough bed, the bed-form and its roughness can effectively alter the time-averaged spatial velocity and turbulence characteristics, particularly at inner flow region; thus, the water-worked bedform should impact the flow characteristics especially at near-bed flow.…”

Section: Introductionmentioning

confidence: 99%

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Velocity Distribution and 3D Turbulence Characteristic Analysis for Flow over Water-Worked Rough Bed

Wei

Huang

2017

Water

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Abstract:To reproduce the natural flow topography in a laboratory environment, it is crucial to recapture its bed condition in order to ensure the accurate representation. Water-worked bed represents a state-of-the-art experimentally formed bed to imitate the natural-formed channel in most rivers or natural streams. Recently, this technique has been intensively studied through experimental and computational approaches; however, its actual influence towards the near-bed flow as compared to experimentally prepared rough bed in well-packed bedform order are still yet to be investigated deeply. This experimental study systematically investigated and compared the differences in velocity distribution and three-dimensional (3D) turbulence characteristics, including turbulence intensities and Reynolds stresses, between uniform smooth bed, laboratory-prepared rough bed and water-worked bed open channel flows. The flow comparisons were concentrated at near-bed region where clear flow behaviour change can be observed. Through these comparisons, the study inspected the characteristics of water-worked bedform thoroughly, in order to inform future experimental research that tries to reproduce natural stream behaviours.

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Section: Turbulence Characteristicssupporting

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Velocity Distribution and 3D Turbulence Characteristic Analysis for Flow over Water-Worked Rough Bed

Wei

Huang

2017

Water

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“…The time varying spatially averaged shear stress contributions are examined following the stress partitioning scheme presented in Coleman et al . [] and Rodriguez‐Abudo and Foster []:

τ_{x z} (z, \overset{t}{true}) = μ \frac{\partial 〈 \overset{u}{true} 〉}{\partial z} - ρ 〈 \overset{u}{true} 〉 〈 \overset{w}{true} 〉 - ρ 〈 {false(\tilde{u} false)}_{b} {false(\tilde{w} false)}_{b} 〉 - ρ 〈 \overset{u^{'} w^{'}}{true} 〉,

where u is the horizontal velocity ( x ‐coordinate), w is the vertical velocity ( z ‐coordinate),

\tilde{t}

represents the wave phase, over tilde (

\overset{}{true}

) denotes phase average, prime (

'

) represents departure from the phase average (

u_{i} = {\overset{u}{true}}_{i} + u_{i}^{'}

), angle brackets (

〈 〉

) denote spatial average, and the subscript b represents departure from the spatial average (

{\overset{u}{true}}_{i} = 〈 {\overset{u}{true}}_{i} 〉 + {false(\tilde{u} false)}_{b}

). Expression (4) partitions the shear stress into a viscous component (first term), a convective momentum transfer term induced by the large scale hydrodynamics presented by waves and currents (and any other physics coherent with

{\overset{u}{true}}_{i}

, second term), a bed form‐induced momentum transfer term that arises due to the presence of an uneven boundary (third term), and the Reynolds (turbulent) stress (fourth term).…”

Section: Resultsmentioning

confidence: 99%

“…Similar to Coleman et al . []

τ_{L W T} \approx - ρ \overset{u}{true} (z, \overset{t}{true}) \overset{w}{true} (z, \overset{t}{true}),

where

\tilde{u}

and

\tilde{w}

are approximated with LWT:

\overset{u}{true} (z, \overset{t}{true}) \approx \frac{π H}{T} \frac{\cosh k z}{\sinh k h} \cos (- ω \overset{t}{true})

\overset{w}{true} (z, \overset{t}{true}) \approx \frac{π H}{T} \frac{\sinh k z}{\sinh k h} \sin (- ω \overset{t}{true}) .

…”

Section: Resultsmentioning

confidence: 99%

Direct estimates of friction factors for a mobile rippled bed

Rodriguez-Abudo

Foster

2017

JGR Oceans

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New friction factor estimates are computed from the total momentum transfer applied to a rippled sediment bed. The total time‐dependent momentum flux is achieved by implementing the double‐averaged horizontal momentum equation on the nearbed flow field collected with PIV. Time‐independent friction factors are obtained by regressing the total momentum flux to the common quadratic stress law given by 12ρu∞|u∞|. The resulting friction factors compare favorably with available analysis techniques including energy dissipation, vertical turbulence intensity, and maximum shear stress, but can be 2‐6 times smaller than estimates determined with the model by Madsen (1994) and the formula of Swart (1974) using the ripple roughness.

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“…It appears however that in terms of the magnitude,τ is generally lower than the shear stresses presented in figure 19, as was also the case for the other experiments, which are not presented here for brevity. The fact thatτ close to the bed is consistently lower than the bed shear stress estimates in figure 19 could be due to the presence of significant form-induced stresses which are not captured in (6.3), but require estimation of the the spatial-and time-averaged Reynolds equations (Coleman, Nikora & Schlicke 2008).…”

Section: Momentum Integralmentioning

confidence: 89%

Experimental study of the turbulent boundary layer in acceleration-skewed oscillatory flow

O’Donoghue

Davies

et al. 2011

J. Fluid Mech.

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Experiments have been conducted in a large oscillatory flow tunnel to investigate the effects of acceleration skewness on oscillatory boundary layer flow over fixed beds. As well as enabling experimental investigation of the effects of acceleration skewness, the new experiments add substantially to the relatively few existing detailed experimental datasets for oscillatory boundary layer flow conditions that correspond to full-scale sea wave conditions. Two types of bed roughness and a range of highReynolds-number, Re ∼ O(10 6 ), oscillatory flow conditions, varying from sinusoidal to highly acceleration-skewed, are considered. Results show the structure of the intrawave velocity profile, the time-averaged residual flow and boundary layer thickness for varying degrees of acceleration skewness, β. Turbulence intensity measurements from particle image velocimetry (PIV) and laser Doppler anemometry (LDA) show very good agreement. Turbulence intensity and Reynolds stress increase as the flow accelerates after flow reversal, are maximum at around maximum free-stream velocity and decay as the flow decelerates. The intra-wave turbulence depends strongly on β but period-averaged turbulent quantities are largely independent of β. There is generally good agreement between bed shear stress estimates obtained using the loglaw and using the momentum integral equation, and flow acceleration skewness leads to high bed shear stress asymmetry between flow half-cycles. Turbulent Reynolds stress is much less than the shear stress obtained from the momentum integral; analysis of the stress contributors shows that significant phase-averaged vertical velocities exist near the bed throughout the flow cycle, which lead to an additional shear stress, −ρũw; near the bed this stress is at least as large as the turbulent Reynolds stress.

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Spatially-averaged oscillatory flow over a rough bed

Cited by 11 publications

References 27 publications

Velocity Distribution and 3D Turbulence Characteristic Analysis for Flow over Water-Worked Rough Bed

Velocity Distribution and 3D Turbulence Characteristic Analysis for Flow over Water-Worked Rough Bed

Direct estimates of friction factors for a mobile rippled bed

Experimental study of the turbulent boundary layer in acceleration-skewed oscillatory flow

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