Very-Large-Scale Motions in the Atmospheric Boundary Layer Educed by Snapshot Proper Orthogonal Decomposition

Shah, Stimit; Bou‐Zeid, Elie

doi:10.1007/s10546-014-9950-2

Cited by 53 publications

(39 citation statements)

References 52 publications

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“…The differences are due to the distance scaling in the Briggs (1973) model being different from the LES. While there are other analytical models for distance-specific dispersion coefficients, the Briggs (1973) model actually matches the LES profiles better across the range of sites explored here than several other common models (Gifford Jr., 1976;Smith, 1968; see Figs. S8-S11 and Appendix A).…”

Section: Intensive Field Sitesmentioning

confidence: 73%

“…To optimize sampling there are two important variables: (1) the number of measurements and (2) the time interval between measurements. Increasing the number of measurements is expected to increase the accuracy of the retrieval; however, the time interval may also affect results as measurements with short spacing may resample the same coherent plume and thus the same plume realization (Metzger at al., 2007;Shah and Bou-Zeid, 2014).…”

Section: Large Eddy Simulationmentioning

confidence: 99%

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Quantifying uncertainties from mobile-laboratory-derived emissions of well pads using inverse Gaussian methods

Caulton

Bou‐Zeid

et al. 2018

Atmos. Chem. Phys.

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Mobile laboratory measurements provide information on the distribution of CH 4 emissions from point sources such as oil and gas wells, but uncertainties are poorly constrained or justified. Sources of uncertainty and bias in ground-based Gaussian-derived emissions estimates from a mobile platform were analyzed in a combined field and modeling study. In a field campaign where 1009 natural gas sites in Pennsylvania were sampled, a hierarchical measurement strategy was implemented with increasing complexity. Of these sites, ∼ 93 % were sampled with an average of 2 transects in < 5 min (standard sampling), ∼ 5 % were sampled with an average of 10 transects in < 15 min (replicate sampling) and ∼ 2 % were sampled with an average of 20 transects in 15-60 min. For sites sampled with 20 transects, a tower was simultaneously deployed to measure highfrequency meteorological data (intensive sampling). Five of the intensive sampling sites were modeled using large eddy simulation (LES) to reproduce CH 4 concentrations in a turbulent environment. The LES output and LES-derived emission estimates were used to compare with the results of a standard Gaussian approach. The LES and Gaussian-derived emission rates agreed within a factor of 2 in all except one case; the average difference was 25 %. A controlled release was also used to investigate sources of bias in either technique. The Gaussian method agreed with the release rate more closely than the LES, underlining the importance of inputs as sources of uncertainty for the LES. The LES was also used as a virtual experiment to determine an optimum number of repeat transects and spacing needed to produce repre-sentative statistics. Approximately 10 repeat transects spaced at least 1 min apart are required to produce statistics similar to the observed variability over the entire LES simulation period of 30 min. Sources of uncertainty from source location, wind speed, background concentration and atmospheric stability were also analyzed. The largest contribution to the total uncertainty was from atmospheric variability; this is caused by insufficient averaging of turbulent variables in the atmosphere (also known as random errors). Atmospheric variability was quantified by repeat measurements at individual sites under relatively constant conditions. Accurate quantification of atmospheric variability provides a reasonable estimate of the lower bound for emission uncertainty. The uncertainty bounds calculated for this work for sites with >50 ppb enhancements were 0.05-6.5q (where q is the emission rate) for single-transect sites and 0.5-2.7q for sites with 10+ transects. More transects allow a mean emission rate to be calculated with better precision. It is recommended that future mobile monitoring schemes quantify atmospheric variability, and attempt to minimize it, under representative conditions to accurately estimate emission uncertainty. These recommendations are general to mobile-laboratory-derived emissions from other sources that can be treated as point sources.

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Section: Intensive Field Sitesmentioning

confidence: 73%

Section: Large Eddy Simulationmentioning

confidence: 99%

Quantifying uncertainties from mobile-laboratory-derived emissions of well pads using inverse Gaussian methods

Caulton

Bou‐Zeid

et al. 2018

Atmos. Chem. Phys.

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“…This persistence or even increasing dominance of large-scale modes under stable stratification in the near-wall region is also seen in a spectral analysis (not shown): the agreement of the length scale of these large-scale modes in Ekman flow (≈5δ as inferred from the correlation plots in figure 8) with that of the global modes under neutral stratification points to a link between them. While the presence of such large-scale modes and their emergence or persistence in stratified conditions (perhaps related to inertia-gravity waves) is a well-known feature in the core region of channel flow (García-Villalba & del Álamo 2011) and the outer region of Ekman flow (Shah & Bou-Zeid 2014a), such modes of motion were not described near the wall so far (in fact, García-Villalba & del Álamo describe wall turbulence without global modes). We propose -in analogy to the presence of external intermittency in the surface layer under neutral stratification (cf.…”

Section: External Intermittency and The Logarithmic Law For Ekman Flowmentioning

confidence: 99%

Analyses of external and global intermittency in the logarithmic layer of Ekman flow

Ansorge

Mellado

2016

J. Fluid Mech.

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Existence of non-turbulent flow patches in the vicinity of the wall of a turbulent flow is known as global intermittency. Global intermittency challenges the conventional statistics approach when describing turbulence in the inner layer and calls for the use of conditional statistics. We extend the vorticity-based conditioning of a flow to turbulent and non-turbulent sub-volumes by a high-pass filter operation. This modified method consistently detects non-turbulent flow patches in the outer and inner layers for stratifications ranging from the neutral limit to extreme stability, where the flow is close to a complete laminarization. When applying this conditioning method to direct numerical simulation data of stably stratified Ekman flow, we find the following. First, external intermittency has a strong effect on the logarithmic law for the mean velocity in Ekman flow under neutral stratification. If instead of the full field, only turbulent sub-volumes are considered, the data fit an idealized logarithmic velocity profile much better; in particular, a problematic dip in the von Kármán measure κ in the surface layer is decreased by approximately 50 % and our data only support the reduced range 0.41 κ 0.43. Second, order-one changes in turbulent quantities under strong stratification can be explained by a modulation of the turbulent volume fraction rather than by a structural change of individual turbulence events; within the turbulent fraction of the flow, the character of individual turbulence events measured in terms of turbulence dissipation rate or variance of velocity fluctuations is similar to that under neutral stratification.

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“…The Fourier-based pseudo-spectral collocation method (Orszag, 1970;Orszag and Pao, 1975;Canuto et al, 2006) remains the preferred "work-horse" in simulations of wall-bounded flows over horizontally periodic regular domains, which is often used in conjunction with a centered finite-difference or Chebychev polynomial expansions in the vertical direction (Shah and Bou-Zeid, 2014;Moeng and Sullivan, 2015). This approach is often used because of the high-order accuracy and the intrinsic 30 efficiency of the fast-Fourier-transform algorithm (Cooley and Tukey, 1965;Frigo and Johnson, 2005).…”

Section: Discussionmentioning

confidence: 99%

Comparison of dealiasing schemes in large-eddy simulation of neutrally-stratified atmospheric boundary-layer type flows

Margairaz

Giometto

Parlange

et al. 2017

Preprint

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Abstract. Three dealiasing schemes for large-eddy simulation of turbulent flows are inter-compared for the canonical case of pressure-drive atmospheric boundary-layer type flows. Aliasing errors arise in the multiplication of partial sums, such as those encountered when integrating the non-linear terms of the Navier-Stokes equations in spectral methods (Fourier or polynomial discrete series), and are detrimental to the accuracy of the numerical solution. This is of special relevance when using highorder schemes. In this work, a performance/cost analysis is developed for three well-accepted approaches: the exact 3/2 rule, 5 the Fourier truncation method, and a high order Fourier smoothing method. Tests are performed within a newly developed mixed pseudo-spectral collocation -finite differences large-eddy simulation code, parallelized using a two-dimensional pencil decomposition. The static Smagorinsky eddy-viscosity model with wall damping of the model coefficient is used. A series of simulations are performed at varying resolution and key flow statistics are inter-compared among the considered dealiasing schemes. The numerical results validate the numerical performance predicted by theory when using the Fourier truncation and 10 Fourier smoothing methods. In terms of turbulence statistics, the Fourier Truncation method proves to be over-dissipative when compared against the Fourier Smoothing method and the traditional 3/2-rule, leading to an enhanced horizontal integrated mass flux and to higher dispersive momentum fluxes. Its use in large-eddy simulation of atmospheric boundary-layer type flows is therefore not recommended. Conversely, the Fourier Smoothing method yields accurate flow statistics, comparable to those resulting from the application of the 3/2 rule, with a significant reduction in computational cost, which makes it a convenient 15 alternative for use in the studies related to the atmospheric boundary layer.

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Very-Large-Scale Motions in the Atmospheric Boundary Layer Educed by Snapshot Proper Orthogonal Decomposition

Cited by 53 publications

References 52 publications

Quantifying uncertainties from mobile-laboratory-derived emissions of well pads using inverse Gaussian methods

Quantifying uncertainties from mobile-laboratory-derived emissions of well pads using inverse Gaussian methods

Analyses of external and global intermittency in the logarithmic layer of Ekman flow

Comparison of dealiasing schemes in large-eddy simulation of neutrally-stratified atmospheric boundary-layer type flows

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