LES validation of urban flow, part I: flow statistics and frequency distributions

Hertwig, Denise; Patnaik, Gopal; Leitl, Bernd

doi:10.1007/s10652-016-9507-7

Cited by 41 publications

(20 citation statements)

References 60 publications

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“…For the pollutant concentrations the experimental data by Pavageau and Schatzmann [31], Meroney et al [32], Pavageau [33], and Hoydysh and Dabberdt [74] are employed. The quantitative comparison follows well-known metrics (i.e., FAC2, FB, and NMSE) proposed by collaborative projects such as the COST Action 732 [75], according to the works of Hanna [76] and Chang and Hanna [77], and recently for the validation of LES, e.g., [25,78,79].…”

Section: Resultsmentioning

confidence: 99%

Qualitative and Quantitative Investigation of Multiple Large Eddy Simulation Aspects for Pollutant Dispersion in Street Canyons Using OpenFOAM

et al. 2019

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Air pollution is probably the single largest environment risk to health and urban streets are the localized, relevant hotspots. Numerous studies reviewed the state-of-the-art models, proposed best-practice guidelines and explored, using various software, how different approaches (e.g., Reynolds-averaged Navier–Stokes (RANS), large eddy simulations (LES)) inter-compare. Open source tools are continuously attracting interest but lack of similar, extensive and comprehensive investigations. At the same time, their configuration varies significantly among the related studies leading to non-reproducible results. Therefore, the typical quasi-2D street canyon geometry was selected to employ the well-known open-source software OpenFOAM and to investigate and validate the main parameters affecting LES transient simulation of a pollutant dispersion. In brief, domain height slightly affected street level concentration but source height had a major impact. All sub-grid scale models predicted the velocity profiles adequately, but the k-equation SGS model best-resolved pollutant dispersion. Finally, an easily reproducible LES configuration is proposed that provided a satisfactory compromise between computational demands and accuracy.

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Section: Resultsmentioning

confidence: 99%

Qualitative and Quantitative Investigation of Multiple Large Eddy Simulation Aspects for Pollutant Dispersion in Street Canyons Using OpenFOAM

et al. 2019

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“…Urban vegetation plays an important role in UBL flows, explicated by Giometto et al [20] in an LES study featuring a suburban setting. Furthermore, the validation study featuring real urban complexity (but without trees) documented in References [21,22] provides a relevant account of validation approaches, some of which are adopted and expanded upon in this work. Unfortunately, the resolution of their LES model was clearly insufficient to demonstrate the full capacity of LES in urban flow problems.…”

Section: Introductionmentioning

confidence: 99%

Study of Realistic Urban Boundary Layer Turbulence with High-Resolution Large-Eddy Simulation

et al. 2020

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This study examines the statistical predictability of local wind conditions in a real urban environment under realistic atmospheric boundary layer conditions by means of Large-Eddy Simulation (LES). The computational domain features a highly detailed description of a densely built coastal downtown area, which includes vegetation. A multi-scale nested LES modelling approach is utilized to achieve a setup where a fully developed boundary layer flow, which is also allowed to form and evolve very large-scale turbulent motions, becomes incident with the urban surface. Under these nonideal conditions, the local scale predictability and result sensitivity to central modelling choices are scrutinized via comparative techniques. Joint time–frequency analysis with wavelets is exploited to aid targeted filtering of the problematic large-scale motions, while concepts of information entropy and divergence are exploited to perform a deep probing comparison of local urban canopy turbulence signals. The study demonstrates the utility of wavelet analysis and information theory in urban turbulence research while emphasizing the importance of grid resolution when local scale predictability, particularly close to the pedestrian level, is sought. In densely built urban environments, the level of detail of vegetation drag modelling description is deemed most significant in the immediate vicinity of the trees.

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“…The use of PIV for the validations is, however, still rare [4,19,20]. Since there may be a lack of a sufficiently long time period from LES or from PIV to achieve legitimate statistical averages, a feasible strategy for the validation of LES is, according to Hertwig et al [20], not only the comparison of mean values but also a multi-point time-series analysis by means of advanced statistical tools, which allows us to detect transient structures, their shape and also frequency distribution.In this paper, we present an extension of a validation procedure introduced by the research of [20][21][22] and Hertwig [23], in which a three-level validation hierarchy, consisting of global statistics, eddy statistics and flow structure statistics was employed. The extension comprises time-series analyses such as the spectral and spatial modification of the quadrant analysis, and the temporally-spatial analyses, namely the spatial correlation or the Proper Orthogonal Decomposition (POD).…”

mentioning

confidence: 99%

“…In this paper, we present an extension of a validation procedure introduced by the research of [20][21][22] and Hertwig [23], in which a three-level validation hierarchy, consisting of global statistics, eddy statistics and flow structure statistics was employed. The extension comprises time-series analyses such as the spectral and spatial modification of the quadrant analysis, and the temporally-spatial analyses, namely the spatial correlation or the Proper Orthogonal Decomposition (POD).…”

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confidence: 99%

On Street-Canyon Flow Dynamics: Advanced Validation of LES by Time-Resolved PIV

et al. 2018

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The advanced statistical techniques for qualitative and quantitative validation of Large Eddy Simulation (LES) of turbulent flow within and above a two-dimensional street canyon are presented. Time-resolved data from 3D LES are compared with those obtained from time-resolved 2D Particle Image Velocimetry (PIV) measurements. We have extended a standard validation approach based solely on time-mean statistics by a novel approach based on analyses of the intermittent flow dynamics. While the standard Hit rate validation metric indicates not so good agreement between compared values of both the streamwise and vertical velocity within the canyon canopy, the Fourier, quadrant and Proper Orthogonal Decomposition (POD) analyses demonstrate very good LES prediction of highly energetic and characteristic features in the flow. Using the quadrant analysis, we demonstrated similarity between the model and the experiment with respect to the typical shape of intensive sweep and ejection events and their frequency of appearance. These findings indicate that although the mean values predicted by the LES do not meet the criteria of all the standard validation metrics, the dominant coherent structures are simulated well.For turbulent boundary-layer flow problems, the best data sources are field measurements. Unfortunately, field measurements are very rarely available and, as Schatzmann and Leitl [3] pointed out, the micro-meteorological flow found in field measurements exhibits much larger scatter than the data from a closely-controlled wind-tunnel experiment. Therefore, field data represent a greater challenge in terms of post-processing and preparation for a validation. Thus, the CFD results are often compared with those from wind-tunnel experiments [4][5][6][7][8][9]. That said, the CFD validations against data from street-canyon field experiments were performed as well (e.g., [10][11][12]).A validation procedure for atmospheric boundary layer dispersion or velocity distribution predictions by CFD was compiled within the frame of COST 732 [13][14][15], COST C14 [16] and AIJ Tominaga et al. [17]. These guidelines addressed various types of models including Gaussian models, and RANS and LES models. The latter, LES model, represents an affordable combination of direct simulation of large turbulent structures while modelling small unresolved scales by means of an embedded sub-grid model [18].Since common validation techniques target just the variables that are available from all the discussed models, only temporally-averaged values are usually retrieved for comparison. Illustrative applications of the validation of temporally-averaged values from LES against various experiments can be found in Jimenez and Moser [18]. The most suitable experimental data currently available are those obtained from Particle Image Velocimetry (PIV) measurement techniques as they can provide multi-points time-resolved synchronised data. The use of PIV for the validations is, however, still rare [4,19,20]. Since there may be a lack of a sufficiently long ...

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LES validation of urban flow, part I: flow statistics and frequency distributions

Cited by 41 publications

References 60 publications

Qualitative and Quantitative Investigation of Multiple Large Eddy Simulation Aspects for Pollutant Dispersion in Street Canyons Using OpenFOAM

Qualitative and Quantitative Investigation of Multiple Large Eddy Simulation Aspects for Pollutant Dispersion in Street Canyons Using OpenFOAM

Study of Realistic Urban Boundary Layer Turbulence with High-Resolution Large-Eddy Simulation

On Street-Canyon Flow Dynamics: Advanced Validation of LES by Time-Resolved PIV

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