On the wall structure of the turbulent boundary layer

Blackwelder, Ron F.; Kaplan, R.

doi:10.1017/s0022112076003145

Cited by 600 publications

(289 citation statements)

References 17 publications

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“…Blackwelder & Kaplan 1976;Blackwelder 1978;Praturi & Brodkey 1978;Smith & Schwartz 1983). Smith et al (1991) make convincing arguments that the low-speed streaks are, in fact, artefacts of the passage of symmetric and asymmetric hairpin vortices.…”

Section: Introductionmentioning

confidence: 98%

Three-dimensional structure of a low-Reynolds-number turbulent boundary layer

2004

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A low-Reynolds-number zero-pressure-gradient incompressible turbulent boundary layer was investigated using a volumetric imaging technique. The Reynolds number based on momentum thickness was 700. The flow was tagged with a passive scalar from two spanwise dye slots to distinguish between fluid motions originating in the inner and outer portions of the boundary layer. The resulting volumetric scalar field was interrogated using a laser sheet scanner developed for this study. Twoand three-dimensional time-dependent visualizations of a 50 volume time series are presented (equivalent to 17δ in length). In the outer portion of the boundary layer, scalar structures were observed to lie along lines in the (x, z)-plane, inclined to the streamwise (x-)direction in the range ±50 • . The ejection of brightly dyed fluid packets from the near-wall region was observed to be spatially organized, and related to the passage of the large-scale scalar structures. IntroductionHere, we present the short-term dynamics of a low-Reynolds-number turbulent boundary layer using three-dimensional visualizations of the scalar field. The interpretations are based on inspection of individual events in a data set comprising a 50 volume time series, equivalent to 17δ in length.It is a well-established observation that a turbulent boundary layer displays structure, in that 'coherent motions' or 'organized motions' are recognized to be an important component of the velocity and pressure fields. Such coherent structures were described by Robinson (1991) as 'a three-dimensional region of the flow over which at least one fundamental flow variable (velocity component, density, temperature, etc.) exhibits significant correlation with itself or with another flow variable over a range of space and/or time that is significantly larger than the smallest local scales of the flow.' Different features appear in the near-wall and outer-layer regions, and we have a broad understanding of their general features. In contrast, the fundamental nature of the motions, their distinguishing characteristics, and the nature of their interactions, are not at all settled. According to an early review by Cantwell (1981), the structure

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Section: Introductionmentioning

confidence: 98%

Three-dimensional structure of a low-Reynolds-number turbulent boundary layer

2004

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“…Suspension of sediments is often related to large scale turbulence structures associated with clusters of ejections (Bennett et al, 1998;Kawanisi and Yokosi, 1993). Blackwelder and Kaplan, 1976;Bogard and Tiederman, 1986;Keylock, 2007;Wu and Yang, 2004), and its value is chosen arbitrarily (Keylock, 2008) or ignored altogether (Keylock et al, 2014). As the threshold increases, the number of exceedances decreases, biasing the stress magnitude to be mostly contributed by ejections within the second quadrant (Keylock, 2007;Willmarth and Lu, 1972).…”

Section: Introductionmentioning

confidence: 99%

Wave-induced coherent turbulence structures and sediment resuspension in the nearshore of a prototype-scale sandy barrier beach

Kassem

Thompson

Amos

et al. 2015

Continental Shelf Research

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Abstract:The suspension of sediments by oscillatory flows is a complex case of fluid-particle interaction. The aim of this study is to provide insight into the spatial (time) and scale (frequency) relationships between wave-generated boundary layer turbulence and eventdriven sediment transport beneath irregular shoaling and breaking waves in the nearshore of a prototype sandy barrier beach, using data collected through the Barrier Dynamics Experiment II (BARDEX II). Statistical, quadrant and spectral analyses reveal the anisotropic and intermittent nature of Reynolds' stresses (momentum exchange) in the wave boundary layer, in all three orthogonal planes of motion. The fractional contribution of coherent turbulence structures appears to be dictated by the structural form of eddies beneath plunging and spilling breakers, which in turn define the net sediment mobilisation towards or away from the barrier, and hence ensuing erosion and accretion trends. A standing transverse wave is also observed in the flume, contributing to the substantial skewness of spanwise turbulence. Observed low frequency suspensions are closely linked to the mean flow (wave) properties. Wavelet analysis reveals that the entrainment and maintenance of sediment in suspension through a cluster of bursting sequence is associated with the passage of intermittent slowly-evolving large structures, which can modulate the frequency of smaller motions. Outside the boundary layer, small scale, higher frequency turbulence drives the suspension. The extent to which these spatially varied perturbation clusters persist is associated with suspension events in the high frequency scales, decaying as the turbulent motion ceases to supply momentum, with an observed hysteresis effect. The suspension of sediment in turbulent flows is a complex case of fluid-particle interaction, governed by shear stresses (momentum exchanges) at the bed and within the benthic boundary layer (BBL). Defining the physical processes which dictate the resuspension of sediments in coastal and estuarine settings is fundamental for accurate predictions of bed morphology evolution (Van Rijn et al., 2007), and has profound implications for the biogeochemical processes that shape their local ecology (Thompson et al., 2011). It is also a prerequisite to quantifying erosion and deposition trends, and hence guiding engineering applications such as beach nourishment, defence schemes against erosion and flooding, maintenance of marine infrastructure and waterways, and aggregate dredging. There is a genuine need for better, robust models of suspended sediment transport in the coastal zone (Aagaard and Jensen, 2013). In a vision paper on future research needs in coastal dynamics, Van Rijn et al. (2013) highlighted the pressing need for research to support such models, focusing in particular on sand transport in the shoreface (non-breaking waves), surf and swash zones; employing field and controlled laboratory experiments.The mobilisation of sediments in the nearshore and shoreface is dominated b...

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“…The latter interaction scenario could have an influence on the friction drag or separation behavior of the BL. The main carriers of kinetic energy in a turbulent BL are the larger eddies with characteristic frequencies far below 10 kHz (at wind speeds around 60m/s) (Blackwelder et al 1976 andSchlichting et al 2000). Thus an interaction with ultrasound is not plausible.…”

Section: Operating Frequency Rangementioning

confidence: 99%

Optically interrogated MEMS pressure sensor array

et al. 2011

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A novel pressure measurement technique is developed with the objective to simplify wind tunnel investigations while providing full field measurement capability with highest measurement performance. The static pressure distributions are recorded by interferometric means using an array of silicon diaphragm microresonators as pressure sensing elements. They are remotely excited into free vibration using a capacitive ultrasound transducer (CUT) transmitting high power narrow band (50 -80kHz) acoustic noise. Dependent on their quasi-static deflection caused by a pressure load the resonance frequency varies with an average pressure sensitivity of 3Hz/Pa at 70kHz. Further requirements for the system performance are a maximum pressure, temporal and spatial resolution of 0.2% of FS (10kPa), 1Hz and 5mm, respectively.

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On the wall structure of the turbulent boundary layer

Cited by 600 publications

References 17 publications

Three-dimensional structure of a low-Reynolds-number turbulent boundary layer

Three-dimensional structure of a low-Reynolds-number turbulent boundary layer

Wave-induced coherent turbulence structures and sediment resuspension in the nearshore of a prototype-scale sandy barrier beach

Optically interrogated MEMS pressure sensor array

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