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  • 11
    Electronic Resource
    Electronic Resource
    Dispersion in sheared Gaussian homogeneous turbulence (1993)
    Springer
    Boundary layer meteorology 62 (1993), S. 281-290 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract By integrating the Fokker-Planck equation corresponding to a Lagrangian stochastic trajectory model, which is consitent with the selection criterion of Thomson (1987), an analytical solution is given for the joint probability density functionp(xi, ui, t) for the position (x i) and velocity (u i) at timet of a neutral particle released into linearly-sheared, homogeneous turbulence. The solution is compared with dispersion experiments conforming to the restrictions of the model and with a shortrange experiment performed in highly inhomogeneous turbulence within and above a model crop canopy. When the turbulence intensity, wind shear and covariance are strong, the present solution is better than simpler solutions (Taylor, 1921; Durbin, 1983) and as good as any numerical Lagrangian stochastic model yet reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00705559
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  • 12
    Electronic Resource
    Electronic Resource
    Coherent motions in windbreak flow (1994)
    Springer
    Boundary layer meteorology 70 (1994), S. 151-169 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Experimental data on windbreak flows have been analysed, using several statistical methods. Our analysis demonstrates that coherent structures exist in the mixing region of a porous windbreak (50% porosity) flow, and are largely responsible for the momentum transport that re-accelerates the leeward flow. A comparison between windbreak flow and laboratory turbulent mixing layers suggests that the dominant structures in these two flows are similar. Some previous numerical and experimental results are interpreted in light of the coherent structures and the self-similar property in the mixing region of a windbreak flow.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00712527
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  • 13
    Electronic Resource
    Electronic Resource
    Numerical simulation of particle trajectories in inhomogeneous turbulence, II: Systems with variable turbulent velocity scale (1981)
    Springer
    Boundary layer meteorology 21 (1981), S. 423-441 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract It is shown that for the purpose of trajectory simulation, the vertical velocityw L (t) of a fluid element, which is moving in a system (such as a forest canopy, or the unstably stratified atmospheric surface layer) whose turbulent velocity scale σ w is height-dependent, must be chosen from a frequency-distribution which is asymmetric aboutw L = 0. If the gradient ∂σ w /∂z varies only slowly with height, correct trajectories may be obtained by adding a bias $$\bar w_L = \Lambda _L \partial \sigma _w /\partial z$$ (where Λ L is the length scale) to a fluctuating velocity chosen from a symmetric distribution with variance σ w 2(z).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02033592
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  • 14
    Electronic Resource
    Electronic Resource
    Numerical simulation of particle trajectories in inhomogeneous turbulence, III: Comparison of predictions with experimental data for the atmospheric surface layer (1981)
    Springer
    Boundary layer meteorology 21 (1981), S. 443-463 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract It is shown that predictions of a numerical trajectory-simulation method agree closely with the Project Prairie Grass observations of the concentrations 100 m downwind of a continuous point source of sulphur dioxide if the height (z) dependence of the Lagrangian length scale Λ L is chosen as: whereL is the Monin-Obukhov length. The value of 0.5 for Λ L /z in neutral conditions is consistent with the findings of Reid (1979) for the Porton experiment, and is also shown to be the best choice for simulation of an experiment in which concentration profiles were measured a short distance (〈 40 m) downwind of an elevated point source of glass beads (40 μn diameter). $$\begin{gathered} \Lambda _L = 0.5z\left( {1 - 6\frac{z}{L}} \right)^{{1 \mathord{\left/ {\vphantom {1 4}} \right. \kern-\nulldelimiterspace} 4}} L〈 0 \hfill \\ \Lambda _L = 0.5z/\left( {1 + 5\frac{z}{L}} \right)L 〉 0 \hfill \\ \end{gathered} $$
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02033593
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  • 15
    Electronic Resource
    Electronic Resource
    Comments on a relationship between fluid and immersed-particle velocity fluctuations proposed by Walklate (1987) (1988)
    Springer
    Boundary layer meteorology 43 (1988), S. 93-98 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00153972
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  • 16
    Electronic Resource
    Electronic Resource
    A second-order closure model for flow through vegetation (1988)
    Springer
    Boundary layer meteorology 42 (1988), S. 371-392 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract By splitting the turbulent kinetic energy into two wavebands and adopting as the turbulence timescale the ratio k/ɛ of the kinetic energy in the low-frequency band to its turnover-rate, the second-order closure scheme of Launder et al. (1975) has been adapted for flow through vegetation. Predictions of the model compare satisfactorily with observations of the mean windspeed and (somewhat less satisfactorily) with the turbulent velocity variances in two very different canopies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00121591
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  • 17
    Electronic Resource
    Electronic Resource
    A two-dimensional trajectory-simulation model for non-Gaussian, inhomogeneous turbulence within plant canopies (1992)
    Springer
    Boundary layer meteorology 61 (1992), S. 349-374 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We report a two-dimensional (alongwind u, vertical w) trajectory-simulation model, consistent with Thomson's (1987) well-mixed criteria, that allows for the non-Gaussian turbulence typical of flow within a plant canopy. The effect of non-Gaussian turbulence was examined by formulating a non-Gaussian u, w joint probability density function (PDF) as the sum of two Gaussian joint-PDFs. The resultant PDF reproduced the desired means, variances, skewnesses, and kurtoses, and the correct covariance. In prediction of the location of maximum concentration downwind of a line source in homogeneous, slightly non-Gaussian turbulence, it proved advantageous to incorporate skewness and kurtosis. However, in the case of inhomogeneous, highly non-Gaussian turbulence, the addition of skewness and kurtosis in the model resulted in substantially worse agreement with measurements than the results of the model using Gaussian PDFs. This may be due to inaccuracy in our PDF formulation. Dispersion predictions from the model with Gaussian PDFs were generally not statistically different from measurements. These results indicate that a two-dimensional Gaussian trajectory-simulation approach is adequate to predict mean concentrations and fluxes resulting from sources within plant canopies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00119097
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  • 18
    Electronic Resource
    Electronic Resource
    Numerical simulation of particle trajectories in inhomogeneous turbulence, I: Systems with constant turbulent velocity scale (1981)
    Springer
    Boundary layer meteorology 21 (1981), S. 295-313 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A means of numerical simulation of particle trajectories in inhomogeneous turbulence is described. The method employs a simple coordinate transformation which allows a trajectory in inhomogeneous turbulence to be converted to a corresponding trajectory in homogeneous turbulence. Concentration distributions predicted by the trajectory-simulation method agree precisely with analytical solutions in the special cases of homogeneous turbulence, turbulence with power-law wind and eddy diffusivity profiles, and the neutral atmospheric surface layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00119275
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  • 19
    Electronic Resource
    Electronic Resource
    Turbulent dispersion in the atmospheric surface layer (1982)
    Springer
    Boundary layer meteorology 22 (1982), S. 399-420 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract By non-dimensionalizing a trajectory-simulation (TS) model of turbulent dispersion, it is shown that the dimensionless concentration z 0cu*/kQ (cu */kQ) due to a continuous line (area) source of strength Q in the atmospheric surface layer depends only on z/z 0, x/z 0, z 0/L and z s/z0, where z s is the source height. The TS model is used to tabulate concentration profiles due to ground-level line and area sources. Concentration profiles generated by the TS model for elevated sources are shown to be inconsistent with the Reciprocal Theorems of Smith (1957) and it is suggested that this is because the flux-mean gradient closure scheme inherent in the Reciprocal Theorem is invalid for an elevated source.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00124701
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  • 20
    Electronic Resource
    Electronic Resource
    An approximate analytical solution to the diffusion equation for short-range dispersion from a continuous ground-level source (1982)
    Springer
    Boundary layer meteorology 23 (1982), S. 85-103 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract An easily-evaluated expression for the dimensionless concentration profile χ(z/z 0,χ/z 0, z 0/L) = = cu */kQ (or z 0cu*/kQ) downwind of a continuous ground-level area (or line) source in the stable surface layer is obtained by integrating the diffusion equation using the Shwetz approximation method (c = concentration, Q = source strength, k = von Kárman's constant). The analytical solution compares closely with concentration profiles obtained using a trajectory-simulation model over a useful range of heights, the important discrepancies occurring at the upper edge of the plume. The analytical solution is used to generate predictions of ground-level concentration for the Project Prairie Grass experiments; good agreement with the observations is obtained at all downwind distances (50 to 800 m).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00116113
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