Pathological cases in turbulent field and spectral approach

Pathological cases, which are defined by reference to standard patterns of flows, the mechanisms of which can supposedly be elucidated, display some failures in previous predictive methods. The role played by several preponderant factors which appear in the equations governing either the evolution of the turbulent kinetic energy or that of the velocity correlation is more or less explained. Mean velocity gradient orders the turbulent structure whereas the rate of strain pressure correlation refrains this trends. Such views can be supported by experimental data; however, if the behavior of some turbulent fields is examined, slight failures appear. In several cases, the reasons of such failures can be found by analyzing the spectral behavior of these turbulent fields. In most cases, the energy flux is constant within the inertial range, all the parts of the spectrum are linked to each other through this scalar quantity. Such a situation can be invalidated if a large amount of energy is introduced in a small spectral area. This peak in spectral space displays the important role of quasi ordered structures; hence, turbulence modellings carried out in physical space should be invalidated unless several characteristic scales are introduced.