Perspectives in turbulences study

Turbulence can be narrowly defined as a property of Newtonian fluid flow of constant density and constant viscosity at high Reynolds number. Most studies to turbulence have an applied objective. An attempt can be made to specify what is the basic problem common to all of these applications, and in what sense this problem is unsolved. The applicability of the Navier- Stokes equation to real turbulent flows and the success and limitations of direct numerical simulation are considered. An assessment of current routes to well posed quantitative description of turbulent flow leads to the overall message: Ensemple averaging isthe only averaging procedure that meets the needs of the aircraft designer. Thus an attempt is made to open new ways in turbulence modelling, emphasis is granted to invariance properties