Abstract
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.
Highlights
Numerical codes for computational fluid dynamics (CFD) have been developed and used in industrial CFD applications where a variety of practical problems are predicted and tested (e.g., [1]).Owing to the enormous complexity of turbulence and extremely variable boundary conditions, the modelling of the micro-meteorological scale has been delayed with respect to their practical implementations
We demonstrate that spatial data from the time-resolved particle image velocimetry (TR-Particle Image Velocimetry (PIV))
The vertical profiles of the dimensionless mean streamwise velocity, U/Ure f, at the centre of the street canyon are compared in Figure 2a, where the PIVa data are displayed with the horizontal bars representing the measurement error derived from the standard deviation (STD) at each elevation
Summary
Numerical codes for computational fluid dynamics (CFD) have been developed and used in industrial CFD applications where a variety of practical problems are predicted and tested (e.g., [1]). Owing to the enormous complexity of turbulence and extremely variable boundary conditions, the modelling of the micro-meteorological scale has been delayed with respect to their practical implementations. After years of intensive development, the numerical codes for near-surface atmospheric flow have attained a level of sufficient precision in mathematical description and spatial resolution. Time-resolving frameworks, such as Large-Eddy Simulation (LES) and Direct Numerical. Simulation (DNS), have the potential to become truly credible calculation tools for solving air quality issues since these models are capable of capturing the time-dependent behaviour of turbulence. The CFD model needs to undergo a thorough validation procedure before its practical implementation. The validation determines to what extent the model is in agreement with real physics
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