Methods for Strong Turbulence III. Model Based on Reduced Variables
By a reduction of variables, specific processes in inhomogeneous turbulence may be studied. Global perturbations that are selectively chosen by boundary conditions are sometimes excited. In such a case, a truncated model is often used, and a few degrees of freedom for the global perturbations are kept. A typical example is the Lorenz model in fluid dynamics [16.1]. When a cascade plays a dominant role, the shell model is a useful approach [3.19–3.22]. The shell model for a system with linear instabilities will be discussed here. The third is the K- ε model [16.2]. The influence of the boundary appears through the spatial transport of turbulence. The K- ε model based on the TSDIA is used to study such situations.