B • TURBULENT FLOW 



of spreading of both velocity and temperature. The effect of the tem- 

 perature on the width is given as proportional to [1 + (To — T'i)/T'i]~?. 

 Pabst's work, as quoted by Szablewski, does not provide any test of 

 this effect. The effect is opposite to that found by Corrsin and Uberoi 

 for Ui = 0. 



Conclusion 5 appears to be inconsistent with conclusion 4. Conclusion 

 5 can, however, be made to appear reasonable by following a suggestion 

 by Squire and Trouncer to the effect that compressibility or heating might 

 be dealt with in terms of an "equivalent jet." Since the momentum 



^i)2pC7o(t/o- U^) 



is maintained at all sections, an equivalent incompressible jet should be- 

 have like a compressible jet when the momentum is the same. Heating a 

 jet decreases pUo(Uo — Ui) by decreasing p. We should obtain the same 

 effect without heating by keeping p the same and decreasing Uo{ Uo — Ui) . 

 This can be done either by decreasing Uo or by increasing Ui. By either 

 means Ui/Uo is increased, and this clearly has the effect of decreasing 

 the divergence of the velocity field. Presumably the divergence of the 

 temperature field would follow that of the velocity field. 



The tentative conclusion drawn from the present information is that 

 the effect of density on spreading characteristics reverses in going from 

 the case where t/i = to the case where Ui > 0. More experimental 

 results covering a greater range of conditions are needed to clarify the 

 situation. 



Not all of the information on jets has been covered in this brief 

 survey. Pai, for example, gives a mathematical procedure for dealing 

 with turbulent jets by employing methods analogous to those for laminar 

 flow. For this, the reader is referred to his book [111]. An extensive 

 bibliography given by Forstall and Shapiro [134] will be helpful to readers 

 wishing to pursue the subject of jets further. 



CHAPTER 6. TURBULENT STRUCTURE 

 OF SHEAR FLOWS 



B,33. The Nature of the Subject. Dating from about 1925 many 

 investigators have applied the hot wire anemometer in aerodynamic ex- 

 periments in an effort to learn something about turbulence through meas- 

 urement. Over the years these efforts have borne fruit; consequently there 

 are many separate pieces of information contributing to our present 

 knowledge of turbulence and the turbulent structure of various flow fields. 



< 184 > 



