Introduction

Abstract

Turbulent flows are full of vortexes, the chaotic motion of which possesses a great amount of kinetic energy, mainly in the form of angular rotation. The question is how to find the special features of this state and use them in continuum balances. In engineering the only way is practical, that is, physically measuring forces and calculating the corresponding velocity field. Forces are measured at a plane of gage (across the tube flow section, etc) while energy and impulses are contained in a fluid volume. That is why we need to begin with spatial averaging to determine turbulent flow parameters.

All real fluid motions are rotational. Even in nearly irrotational flows the relatively small amount of vorticity present may be of central importance in determining major flow characteristics, and even some of those whose interest in fluid dynamics is only of the practical sort are now beginning to learn that the hitherto largely neglected question of vorticity must at last be faced.

Clifford Truesdell, 1953