Scale interactions and anisotropy in stable boundary layers

Vercauteren, Nikki; Boyko, Vyacheslav; Faranda, Davide; Stiperski, Ivana

doi:10.1002/qj.3524

Cited by 22 publications

(31 citation statements)

References 44 publications

(87 reference statements)

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“…This is intuitive since turbulence becomes more anisotropic in very stable conditions where the influence of sub‐mesoscale motions is also significant (cf. Stiperski and Calaf, ; Vercauteren et al ., ) or above the BL where geostrophic turbulence is two‐dimensional. In the initiation phase of the katabatic flow, these very stable conditions with anisotropic turbulence are found also very close to the ground as already observed by Banta ( ).…”

Section: Stable Boundary‐layer Heightmentioning

confidence: 99%

On the turbulence structure of deep katabatic flows on a gentle mesoscale slope

Stiperski

Holtslag

Lehner

et al. 2020

Quart J Royal Meteoro Soc

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A comprehensive analysis of the turbulence structure of relatively deep midlatitude katabatic flows (with jet maxima between 20 and 50 m) developing over a gentle (1 • ) mesoscale slope with a long fetch upstream of the Meteor Crater in Arizona is presented. The turbulence structure of flow below the katabatic jet maximum shows many similarities with the turbulence structure of shallower katabatic flows, with decreasing turbulence fluxes with height and almost constant turbulent Prandtl number. Still stark differences occur above the jet maximum where turbulence is suppressed by strong stability, is anisotropic and there is a large sub-mesoscale contribution to the flux. Detecting the stable boundary-layer top depends on the method used (flux-vs. anisotropy-profiles) but both methods are highly correlated. The top of the stable boundary layer, however, mostly deviates from the jet maximum height or the top of the near-surface inversion. The flat-terrain formulations for the boundary-layer height correlate well with the detected top of the stable boundary layer if the near-surface and not the background stratification is used in their formulations; however, they mostly largely overestimate this boundary-layer height. The difference from flat-terrain boundary layers is also shown through the dependence of size of the dominant eddy with height. In katabatic flows the eddy size is semi-constant with height throughout the stable boundary-layer depth, whereas in flat terrain, eddy size varies significantly with height. Flux-gradient and flux-variance relationships show that turbulence data from different stable boundary-layer scaling regimes collapse on top of each other showing that the dominant dependence is not on the scaling regime but on the local stability. K E Y W O R D S boundary-layer depth, low-level jet, scaling regimes, stable boundary layer This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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Section: Stable Boundary‐layer Heightmentioning

confidence: 99%

On the turbulence structure of deep katabatic flows on a gentle mesoscale slope

Stiperski

Holtslag

Lehner

et al. 2020

Quart J Royal Meteoro Soc

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“…Otherwise, the model would need more clusters. According to an earlier similar study (Vercauteren et al 2019a), the TKE exhibits a heavy tail distribution in the strongly stable regime. Consequently, taking the logarithm of the TKE, e t ≡ ln(e M ), and making the distribution more Gaussian effectively reduces the number of clusters needed to describe the intermittent regime.…”

Section: Non-stationary Clustering Based On a Linear-autoregressive-fmentioning

confidence: 77%

Multiscale Shear Forcing of Turbulence in the Nocturnal Boundary Layer: A Statistical Analysis

Boyko¹,

Vercauteren²

2020

Boundary-Layer Meteorol

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The lower nocturnal boundary layer is governed by intermittent turbulence which is thought to be triggered by sporadic activity of so-called sub-mesoscale motions in a complex way. We analyze intermittent turbulence based on an assumed relation between the vertical gradients of the sub-mean scales and turbulence kinetic energy. We analyze high-resolution nocturnal eddy-correlation data from 30-m tower collected during the Fluxes over Snow Surfaces II field program. The non-turbulent velocity signal is decomposed using a discrete wavelet transform into three ranges of scales interpreted as the mean, jet and sub-mesoscales. The vertical gradients of the sub-mean scales are estimated using finite differences. The turbulence kinetic energy is modelled as a discrete-time autoregressive process with exogenous variables, where the latter ones are the vertical gradients of the sub-mean scales. The parameters of the discrete model evolve in time depending on the locally-dominant turbulence-production scales. The three regimes with averaged model parameters are estimated using a subspace-clustering algorithm which illustrates a weak bimodal distribution in the energy phase space of turbulence and sub-mesoscale motions for the very stable boundary layer. One mode indicates turbulence modulated by sub-mesoscale motions. Furthermore, intermittent turbulence appears if the sub-mesoscale intensity exceeds $$10 \%$$ 10 % of the mean kinetic energy in strong stratification.

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“…by showing the evolution of the hemodynamic descriptors in a carousel-type representation [228], including animations. A recent study also extruded a third dimension in the barycentric AIM to contextualize the time evolution of the turbulence characteristics [243]. Interpretations may also be facilitated by visualizing the flow frequency content in different ways [170,171], as well as topology skeleton visualization on the lumen wall or in the near-wall region.…”

Section: Chapter 6 Outlookmentioning

confidence: 99%

Turbulence Descriptors in Arterial Flows : Patient-Specific Computational Hemodynamics

Andersson

2021

Linköping Studies in Science and Technology. Dissertations

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At this very moment, there are literally millions of people who suffer from various types of cardiovascular diseases (CVDs), many of whom will experience reduced quality of life or premature lift expectancy. The detailed underlying pathogenic processes behind many of these disorders are not well understood, but were abnormal dynamics of the blood flow (hemodynamics) are believed to play an important role, especially atypical flow-mediated frictional forces on the intraluminal wall (i.e. the wall shear stress, WSS). Under normal physiological conditions, the flow is relatively stable and regular (smooth and laminar), which helps to maintain critical vascular functions. When these flows encounter various unfavorable anatomical obstructions, the flow can become highly unstable and irregular (turbulent), giving rise to abnormal fluctuating hemodynamic forces, which increase the bloodstream pressure losses, can damage the cells within the blood, as well as impair essential structural and functional regulatory mechanisms. Over a prolonged time, these disturbed flow conditions may promote severe pathological responses and are therefore essential to foresee as early as possible.Clinical measurements of blood flow characteristics are often performed non-invasively by modalities such as ultrasound and magnetic resonance imaging (MRI). High-fidelity MRI techniques may be used to attain a general view of the overall large-scale flow features in the heart and larger vessels but cannot be used for estimating small-scale flow variations nor capture the WSS characteristics. Since the era of modern computers, fluid motion can now also be predicted by computational fluid dynamics (CFD)simulations, which can provide discrete mathematical approximations of the flow field with much higher details (resolution) and accuracy compared to other modalities. CFD simulations rely on the same fundamental principles as weather forecasts, the physical laws of fluid motion, and thus can not only be used to assess the current flow state but also to predict (foresee) important outcome scenarios in e.g. intervention planning. To enable blood flow simulations within certain cardiovascular segments, these CFD models are usually reconstructed from MRI-based anatomical and flow image-data. Today, patient-specific computational hemodynamics are essentially only performed within the research field, where much emphasis is dedicated towards understanding normal/abnormal blood flow physiology, developing better individual-based diagnostics/treatments, and evaluating the results reliability/generality in order to approach clinical applicability.In this thesis, advanced CFD methods were adopted to simulate realistic patient-specific turbulent hemodynamics in constricted arteries reconstructed from MRI data. The main focus was to investigate novel, comprehensive ways to characterize these abnormal flow conditions, in the pursuit of better clinical decision-making tools; from more in-depth analyzes of various turbulence-related tensor characteristics to descrip...

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Scale interactions and anisotropy in stable boundary layers

Cited by 22 publications

References 44 publications

On the turbulence structure of deep katabatic flows on a gentle mesoscale slope

On the turbulence structure of deep katabatic flows on a gentle mesoscale slope

Multiscale Shear Forcing of Turbulence in the Nocturnal Boundary Layer: A Statistical Analysis

Turbulence Descriptors in Arterial Flows : Patient-Specific Computational Hemodynamics

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