Intercomparison of 3D turbulence parameterizations for dispersion models in complex terrain derived from a circulation model

A procedure for estimating 3D turbulent parameters from the outputs of a circulation model to be used as input of a random flight model for complex terrain dispersion simulation is presented. It is based on parameterization schemes for surface layer parameters and wind velocity standard deviation profiles available in the literature. The predictions of various schemes (two for surface layer quantities and three either for the PBL depth or standard deviation profiles) have been compared to observations carried out in the alpine region (south Switzerland) during the second TRANSALP campaign by three Doppler Sodar and two sonic anemometers

An intercomparison of two turbulence closure schemes and four parameterizations for stochastic dispersion models

Two Lagrangian particle models, developed by Luhar and Britter (Atmos. Environ., 23 (1989) 1191) and Weil (J. Atmos. Sci., 47 (1990) 501), satisfying the “well-mixed” condition as prescribed by Thomson (J. Fluid. Mech., 180 (1987) 529), are compared. They differ in the closure scheme used in calculating the probability density function of the random forcing in a convective boundary layer. Four different turbulent parameterizations were used as input to both models. Their performances are evaluated against one of the well-known Willis and Deardorff water tank experiments (Atmos. Environ., 12 (1978) 1305). Predicted and measured ground-level concentrations (g.l.c.), maximum g.l.c. distance, mean plume height and plume vertical spread are presented and discussed

Development and application of the microscale Lagrangian particle dispersion model microspray for the simulation of accidental hydrogen releases

A new version of the Lagrangian dispersion model MicroSpray was developed to simulate the dispersion of light gas emitted at high speed. The model was used and tested in the frame of the BioH2Power Project to describe the accidental release of hydrogen gas at supersonic emission speed. A preliminary analysis of the performance of the model is here proposed versus the data observed during an experimental field campaign carried out in Tuscany (Italy)

MICROSPRAY SIMULATION OF DENSE GAS DISPERSION IN COMPLEX TERRAIN

An extended validation of the new Lagrangian particle model MicroSpray version for dense gas simulation is proposed. MicroSpray simulates the dense gas dispersion in situations characterized by the presence of buildings, other obstacles, complex terrain, and possible occurrence of low wind speed conditions. Its performances are compared to a chlorine railway accident (Macdona), to a field experiment (Kit Fox) and to an atmospheric CFD model

Assessment of dispersion parameterizations through wind data measured by three sonic anemometers in a urban canopy

One year of continuous wind and turbulence measurements at three levels (5, 9 and 25 m) on a mast located in the suburb of the city of Turin were collected. Those recorded during April 2007 are analyzed and their main characteristics are presented and discussed. The analysis includes, at each level, mean, standard deviation, Skewness, Kurtosis for the 3-D wind components and sonic temperature. The integral time scales for the 3-D wind components are also computed and friction velocity and Monin-Obukhov length are determined as well. In particular, the wind standard deviation profiles as a function of stability are compared to the literature predictions for flat undisturbed terrain. It is found that, while the vertical component agrees reasonably well, the horizontal components deviate from the prescribed values, as expected considering the buildings and other obstacles effects and the high percentage of low-wind conditions. Also the integral time scales, estimated by the autocorrelation functions, are compared to the literature predictions, finding significant differences, again attributed to the low-wind speed occurrences

The share of the mean turbulent kinetic energy in the near-neutral surface layer for high and low wind speeds

We examine the dependence on wind speed of the share of the mean turbulent kinetic energy among the three velocity components in the near-neutral surface layer. To contrast the general behaviour and the local effects, four datasets are considered, corresponding to different surfaces and environmental conditions. For high wind speeds (i.e., wind speed ≈ 10 ms^(−1)), the shares are well-defined and about the same for all sites. As wind speed decreases (becoming ≈ 1 ms^(−1)), large record-to-record variability occurs giving, on average, an almost isotropic state for the horizontal velocity components. Through spectral analysis, we relate this behaviour to the low-frequency, submeso motions and to the lack of conditions required by Reynolds averaging. The implications for modelling are also discussed, showing that the wind speed, or a related quantity, must be accounted for, besides stability, in second-order closures