Organized turbulent structures—Link between experimental data and LES

Hertwig, Denise; Leitl, Bernd; Schatzmann, Michael

doi:10.1016/j.jweia.2011.01.002

Cited by 16 publications

(9 citation statements)

References 41 publications

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“…Again, the bold values meet the acceptance criterion of 0.66 as defined in VDI [39] for each velocity component. We adopted this criterion in agreement with other studies (e.g., [15,20]) for all the investigated quantities.…”

Section: Hit Ratementioning

confidence: 86%

“…This representation expresses the highest TKE content in each vector from a statistical point of view. The POD may be applied for both the experimental data (e.g., [20,24,25,46]) and the data obtained from CFD simulations (e.g., [47]). Hence, it provides a valuable tool for comparing the results from numerical modelling with those from a physical experiment.…”

Section: Proper Orthogonal Decompositionmentioning

confidence: 99%

“…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%

“…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 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.…”

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).…”

mentioning

confidence: 99%

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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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Section: Hit Ratementioning

confidence: 86%

Section: Proper Orthogonal Decompositionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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

et al. 2018

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

Hertwig

Patnaik

Leitl³

2016

Environ Fluid Mech

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Essential prerequisites for a thorough model evaluation are the availability of problem-specific, quality-controlled reference data and the use of model-specific comparison methods. The work presented here is motivated by the striking lack of proportion between the increasing use of large-eddy simulation (LES) as a standard technique in micrometeorology and wind engineering and the level of scrutiny that is commonly applied to assess the quality of results obtained. We propose and apply an in-depth, multi-level validation concept that is specifically targeted at the time-dependency of mechanically induced shearlayer turbulence. Near-surface isothermal turbulent flow in a densely built-up city serves as the test scenario for the approach. High-resolution LES data are evaluated based on a comprehensive database of boundary-layer wind-tunnel measurements. From an exploratory data analysis of mean flow and turbulence statistics, a high level of agreement between simulation and experiment is apparent. Inspecting frequency distributions of the underlying instantaneous data proves to be necessary for a more rigorous assessment of the overall prediction quality. From velocity histograms local accuracy limi

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Ten questions concerning modeling of near-field pollutant dispersion in the built environment

Tominaga

Stathopoulos

2016

Building and Environment

148

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Outdoor air pollution is a major current environmental problem. The precise prediction of pollutant concentration distributions in the built environment is necessary for building design and urban environmental assessment. Near-field pollutant dispersion, involving the interaction of a plume and the flow field perturbed by building obstacles, is an element of outdoor air pollution that is particularly complex to predict. Modeling methodologies have been discussed in a wide range of research fields for many years. The modeling approaches are categorized into field measurements, laboratory (wind and water tunnel) experiments, (semi-) empirical models, and computational fluid dynamics (CFD) models. Each of these approaches has advantages and disadvantages. It is therefore important to use due consideration for the underlying theory and limitations when applying these modeling approaches. This paper considers some of the most common questions confronting researchers and practitioners in the modeling of near-field pollutant dispersion in the built environment.

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Organized turbulent structures—Link between experimental data and LES

Cited by 16 publications

References 41 publications

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

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

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

Ten questions concerning modeling of near-field pollutant dispersion in the built environment

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