1,721,017 research outputs found
A semi-analytical model for mean concentration in a convective boundary layer.
No full textA model to predict the mean concentration field in convective conditions is proposed. This model is inspired by the probability density function (pdf) models, retaining their assumption of splitting a plume into updraft and a downdraft components. However, the proposed model is more flexible than the pdf models since it includes the effects of turbulence inhomogeneity and it can be adapted to non-stationary conditions. The formulation of the model ensures that in the limit of zero skewness a traditional Gaussian model is obtained. Thus, the model is applicable to conditions ranging from neutral to unstable. The model is solved numerically, but time consumption is negligible. Despite its simplicity, the model shows good performance compared to classical experiments and to more complex and physically consistent numerical model
Eulerian-Lagrangian modelling of dispersion in a convective boundary layer
No full textA simple Eulerian-Lagrangian dispersion model is proposed. The relative dispersion is treated as a Gaussian puff, whereas the puff trajectory is derived by a Lagrangian particle model. Dispersion in a Convective Boundary Layer has been simulated for three different source heights. A comparison with the classical experiments of Willis and Deardoff is proposed. An overall agreement is obtained in modelling dispersion in a 1-dimensional CBL. It is noteworthy that the proposed model is about 25 times faster than a Lagrangian mode
A simple and fast model to compute concentration moments in a convective boundary layer.
No full textRecently, a modified meandering plume model for concentration fluctuations in a convective boundary layer has been formulated (Atmos. Environ. 34 (2000) 3599). This model is based on a hybrid Eulerian-Lagrangian approach and it accounts for the skewed and inhomogeneous turbulence characteristics of the convective flow. Using the same hypotheses, but eliminating the need for Lagrangian particle model, we propose a generalised approach, that only requires the knowledge of mean concentration field. The proposed model is independent from the method used to obtain the mean concentration field. The evaluation of the concentration fluctuation field needs a computational time of only few seconds on a standard PC. Therefore, the model is suitable for practical applications
Investigation of low-frequency perturbations induced by a step obstacle
No full textFlow perturbation due to the orographic forcing at the top of a steep ridge has been investigated. Spectral and wavelet analyses of longitudinal and vertical wind velocity components highlight the presence of low-frequency perturbations produced by topography. Wavelet kurtosis reveals the intermittent character of these perturbations. The application of a multi-resolution data filter allows the detection of the topographically forced structures and the consequent statistical characterisation. The detected topographically forced structures remain active only for a 15% of the time on average. Nevertheless, they appear very efficient in the momentum transport, accounting for about 50% of the downward momentum flux produced in the low frequency range. Quadrant analysis highlights how topographical forcing produces the weakening of ejections and the strengthening of sweeps at the top of the ridge
- …
