Quasi‐coherent structures in the marine atmospheric surface layer

Boppe, R. S.; Neu, Wayne L.

doi:10.1029/95jc02305

Cited by 37 publications

(21 citation statements)

References 27 publications

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“…There are also numerous experimental observations of turbulent structure in the ASL that are consistent with an elongated structure (e.g. Boppe and Neu 1995;Wilczak and Tillman 1980). It is a source of some confusion that, for some studies, these large-scale atmospheric observations have been compared to the behaviour of near-wall streaks observed in laboratory turbulent boundary layers.…”

Section: Very Large-scale Coherent Motionsmentioning

confidence: 91%

“…In general, it is worth noting that the majority of near-wall cycle studies have been conducted at low Reynolds numbers, where the separation of scales and the influence of larger scales is by definition limited. It must be highlighted that the term 'streaks' as applied to the near-wall cycle refers to a very different scale and class of structure than the 'streaks' commonly referred to in the ASL literature (Wilczak and Tillman 1980;Moeng and Sullivan 1994;Boppe and Neu 1995;Lin et al 1996;Drobinski and Foster 2003;Lu and Porté-Agel 2010). In a further complication, as analysis of coherent structures has progressed into the logarithmic and outer regions, the terms 'sweep' and 'ejection' have more recently been applied to Q2 and Q4 Reynolds shear-stress events associated with larger-scale structures located further from the wall.…”

Section: Near-wall Structurementioning

confidence: 99%

See 1 more Smart Citation

Towards Reconciling the Large-Scale Structure of Turbulent Boundary Layers in the Atmosphere and Laboratory

Hutchins

Chauhan

Marušić

et al. 2012

Boundary-Layer Meteorol

242

247

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A collaborative experimental effort employing the minimally perturbed atmospheric surface-layer flow over the salt playa of western Utah has enabled us to map coherence in turbulent boundary layers at very high Reynolds numbers, Re τ ∼ O(10 6 ). It is found that the large-scale coherence noted in the logarithmic region of laboratory-scale boundary layers are also present in the very high Reynolds number atmospheric surface layer (ASL). In the ASL these features tend to scale on outer variables (approaching the kilometre scale in the streamwise direction for the present study). The mean statistics and two-point correlation map show that the surface layer under neutrally buoyant conditions behaves similarly to the canonical boundary layer. Linear stochastic estimation of the three-dimensional correlation map indicates that the low momentum fluid in the streamwise direction is accompanied by counter-rotating roll modes across the span of the flow. Instantaneous flow fields confirm the inferences made from the linear stochastic estimations. It is further shown that vortical structures aligned in the streamwise direction are present in the surface layer, and bear attributes that resemble the hairpin vortex features found in laboratory flows. Ramp-like high shear zones that contribute significantly to the Reynolds shear-stress are also present in the ASL in a form nearly identical to that found in laboratory flows. Overall, the present findings serve to draw useful connections between the vast number of observations made in the laboratory and in the atmosphere.

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Section: Very Large-scale Coherent Motionsmentioning

confidence: 91%

Section: Near-wall Structurementioning

confidence: 99%

Towards Reconciling the Large-Scale Structure of Turbulent Boundary Layers in the Atmosphere and Laboratory

Hutchins

Chauhan

Marušić

et al. 2012

Boundary-Layer Meteorol

242

247

View full text Add to dashboard Cite

show abstract

“…Many researchers interpret spectral energy peaks in the context of eddy-like flow structures (e.g. Boppe and Neu, 1995), but Tennekes and Lumley (1972, p. 259) note that, even though a single wave-like oscillation may be legitimately associated with a single Fourier frequency, an eddy is associated with many Fourier coefficients and the phase relations among them. This implies that more sophisticated analyses are necessary to decompose a velocity field into eddies.…”

Section: Spectral and Cospectral Analysismentioning

confidence: 99%

Turbulent flow over a dune: Green River, Colorado

Venditti

Bauer

2005

Earth Surf Processes Landf

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Detailed echo-sounder and acoustic Doppler velocimeter measurements are used to assess the temporal and spatial structure of turbulent flow over a mobile dune in a wide, lowgradient, alluvial reach of the Green River. Based on the geometric position of the sensor over the bedforms, measurements were taken in the wake, in transitional flow at the bedform crest, and in the internal boundary layer. Spatial distributions of Reynolds shear stress, turbulent kinetic energy, turbulence intensity, and correlation coefficient are qualitatively consistent with those over fixed, two-dimensional bedforms in laboratory flows. Spectral and cospectral analysis demonstrates that energy levels in the lee of the crest (i.e. wake) are two to four times greater than over the crest itself, with minima over the stoss slope (within the developing internal boundary layer). The frequency structure in the wake is sharply defined with single, dominant peaks. Peak and total spectral and cross-spectral energies vary over the bedform in a manner consistent with wave-like perturbations that 'break' or 'roll up' into vortices that amalgamate, grow in size, and eventually diffuse as they are advected downstream. Fluid oscillations in the lee of the dune demonstrate Strouhal similarity between laboratory and field environments, and correspondence between the peak frequencies of these oscillations and the periodicity of surface boils was observed in the field.

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“…The VBS is unable to measure the small-scale fast fluctuating component of velocity, and the skew plot lacks indicators for the threshold T s . The spectra of the VBS and the ADV show a broad peak on the order of 2 Hz, which indicates the frequency of an energetic mean or dominant eddy size passing the sensor (Boppe and Neu 1995;Venditti and Bennett 2000). In this case, the 2 Hz peak is indicative of the passing of macrotubulence seen visually in the time-series results.…”

Section: Turbulence Measurementsmentioning

confidence: 99%

“…When plotted in variance-preserving form, broad peaks in the spectral energy density correspond to the frequency of an energetic mean or dominant eddy passing the velocity sensor (Boppe and Neu 1995;Venditti and Bennett 2000). Results of scale decomposition and spectral analysis for the VBS and the ADV signals are shown in Fig.…”

Section: Turbulence Measurementsmentioning

confidence: 99%

Time-Average Velocity and Turbulence Measurement Using Wireless Bend Sensors in an Open Channel with a Rough Bed

2013

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This paper is motivated by the need to develop low cost, wireless velocity sensors for hydraulic research and application in streams. A velocity bend sensor (VBS) is a flexible plastic polyimide substrate sheet with an electronic resistor connected to a voltage divider. Drag of a moving fluid bends the sensor, changes the electronic resistance, and produces a voltage drop that can be related to the time-averaged freestream velocity of the fluid. VBSs were tested in a recirculating hydraulic flume with a gravel bed. The VBSs show transition from rigid to elastic bending with increasing freestream velocity, which can be described using dimensionless fluid and beambending properties. The relationship between stream velocity and voltage drop across the circuit is nonlinear. A semitheoretical approach to estimate time-averaged streamwise velocity from the voltage drop based on fluid drag, elastic member bending, and circuit principles is applied and shows good agreement with experimentally derived calibration curves. The triple decomposition theorem and spectral analysis are performed on VBS and acoustic Doppler velocimeter (ADV) time series. Results show that the VBS captures low-frequency characteristics of macroturblence present within the turbulent open channel flow but is unable to measure smaller-scale characteristics of eddy shedding for these hydraulic conditions. Turbulent intensity calculated using VBS data is 12% of that from the ADV attributed to the lack of detection of shedding-sized eddies. But, the linear fit between turbulent intensity from the VBS and ADV suggests that the VBS can be used as a proxy for more detailed turbulent measurements when applied in streams.

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Quasi‐coherent structures in the marine atmospheric surface layer

Cited by 37 publications

References 27 publications

Towards Reconciling the Large-Scale Structure of Turbulent Boundary Layers in the Atmosphere and Laboratory

Towards Reconciling the Large-Scale Structure of Turbulent Boundary Layers in the Atmosphere and Laboratory

Turbulent flow over a dune: Green River, Colorado

Time-Average Velocity and Turbulence Measurement Using Wireless Bend Sensors in an Open Channel with a Rough Bed

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