Fluid Particle Motion in Inhomogeneous and Non-Gaussian Turbulence

It has been proven that modelling turbulent dispersion in the Lagrangian framework is a successful and flexible approach. The effects of inhomogeneity, instationarity and nonGaussianity of turbulence have to be taken into account (Thomson, 1987; Sawford, 1991) and there are questions concerning the modelling of buoyancy (van Dop, 1991) and chemical reactions. As shown recently (Heinz and Schaller, 1993), equations for particle motion, particle potential temperature and mass fractions of chemical components can be determined completely consistent with the exact ones for the means and variances, assuming the approximations of Kolmogorov and Rotta. Moreover, the influence of non-linear terms to the systematic particle motion is discussed for locally Gaussian-distributed fluctuations. However, there arises the question in which extent the consistence with the exact transport equations for the first and second moments determines particle motion, which influence arises from non-Gaussian distributed fluctuations for instance for transport coefficients like the diffusion coefficient or the Lagrangian timescale. To get more insight in the contributions of nonGaussianity and inhomogeneity transport coefficients are calculated here for different non-Gaussian distributed vertical velocity fluctuations coinciding in it means and variances.