ABSTRACT
Fluctuating turbulence is usually represented by its intensity, i.e., by a root-mean-square value. If turbulent components were independently random, they could be described by a normal probability density function, or a Gaussian distribution, determined by the second-order moment, i.e., the turbulence intensity. However, turbulent components are never independently random; they are always correlated with each other in both space and time. In a broad sense, one can describe such correlated fluid parcels by the appellation ‘coherent’. Thus, higher-order moments must also be considered in order to obtain more detailed information concerning turbulence. The third-order moment, the ‘skewness factor’, describes the asymmetry in the probability density function of turbulent fluctuations; it is an important factor that is used to describe bursting events. The fourth-order moment, i.e., ‘flatness factor’, describes the intermittency of turbulence, and it is also an essential property, e.g., (Frenkiel & Klebanoff 1973).
