SECTION B 



TURBULENT FLOW 



G. B. SCHUBAUER 

 C. M. TCHEN 



CHAPTER 1, INTRODUCTION 



B,l. Subject Treatment. Since turbulent flows and their effects are 

 encountered in nearly every case where fluid motion is involved, it be- 

 comes important to know their behavior. It is also important to under- 

 stand the reason for their behavior, not only to formulate laws for practi- 

 cal use, but to satisfy our desire to know and to be able to explain the 

 phenomena with which we deal. 



These dual requirements have been kept in mind in writing this ac- 

 count, and some degree of balance has been attempted. However, greater 

 emphasis is placed on the characteristics of mean flow resulting from the 

 action of turbulence than on the turbulent motions themselves. Since the 

 effects of compressibility and aerodynamic heating are assuming increas- 

 ing importance in modern technology, these have been included wherever 

 possible. The general equations of motion and energy are accordingly ex- 

 pressed in terms of a compressible fluid, and combined thermodynamic 

 and aerodynamic formulations are presented in relation to boundary layer 

 and skin friction effects at high speeds. 



Due to the fact that most of the basic concepts by which we attempt 

 to understand the behavior of turbulent flows are as yet conceived only in 

 terms of incompressible flow, much of the subject must still be treated in 

 these terms. Therefore the more penetrating treatment of wall-bounded 

 flows on the one hand and free turbulent flows on the other are dealt with 

 in terms of incompressible, isothermal flow. The specific subjects covered 

 under these general headings are boundary layers, pipe and channel flows, 

 jets, wakes, and mixing regions. In the case of jets the effects of com- 

 pressibihty and of temperature and density differences are treated. 



It would be misleading to imply that complete coverage can be given 

 to all of the varied aspects of turbulent flow in the space allotted to it 

 here. Certain omissions are therefore inevitable. These include much of 

 the structure of turbulent flow embracing the wealth of information de- 

 rived from hot wire measurements and its theoretical interpretation. A 



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