ABSTRACT
In the study of viscous flows thus far, the transport of momentum across and between fluid layers has been taken to be due solely to activity at the molecular level. In this chapter we introduce the concept of turbulence, which is a much more effective means of momentum transport. By its very nature, turbulence is an extremely complex motion that is very difficult to characterize. In fact, the subject of turbulent flows really constitutes another major branch of the field of fluid mechanics and could easily constitute a fourth part for this text. Instead, we will make an effort to develop an appreciation of the difficulty of the problem while still arriving at some useful engineering applications.
