C,25 • CITED REFERENCES 



Townsend [98] performed experiments to check the theoretical predic- 

 tions and reached the following conclusions : 



1. The reduction of turbulent intensity on the upstream side of the gauze 

 is described by the Taylor-Batchelor theory with adequate accuracy. 



2. The reduction of the total turbulent intensity in passing through a 

 gauze is consistent with the theory except for small values of k, when 

 the observed reduction is greater than predicted. 



3. As predicted by the theory, the turbulence emerging behind the gauze 

 is anisotropic, with the intensities of the lateral components exceeding 

 that of the longitudinal component. The degree of anisotropy is less 

 than the theory predicts. 



The smaller degree of anisotropy is ascribed by Townsend to a 

 possible rapid initial adjustment toward isotropy in the zone of influ- 

 ence of the gauze. Downstream of the gauze, Townsend found that the 

 recovery of isotropy is very slow, but local isotropy is valid within the 

 range of observation in the sense that 



\dx) 2 \dx) 



There is some obvious disagreement between the results of Townsend 

 and the NBS data. Such differences are, however, not unexpected in view 

 of the experimental difficulties attending such measurements. While the 

 effect of damping screens has probably been determined with sufficient 

 accuracy for practical appHcation, further experiments are desirable for 

 checking the theory. 



The NBS data show that the scale of turbulence is not changed by 

 the screen. No extensive experimental results are yet available on the 

 change of spectrum. Some of the results obtained by Townsend do not 

 agree with the theoretical predictions. In making such a comparison, it 

 should be borne in mind that the theory is hnear and the change of 

 spectrum downstream of the screen is not considered in the theory. 



C,25. Cited References. ^^ 



1. Batchelor, G. K. The Theory of Homogeneous Turbulence. Cambridge Univ. 

 Press, 1953. 



2. Lin, C. C. J. Aeronaut. Sci. 23, 453-461 (1956). 



3. Burgers, J. M. Adv. Appl. Mech. 1, 171 (1948). 



4. Burgers, J. M. Proc. Natl. Acad. Amsterdam 53, 247, 393, 718, 732 (1950). 



5. Hopf, E. J. Rat. Mech. and Anal. 1, 87 (1952). 



6. Hopf, E. Commun. on Pure and Appl. Math. 1, 303 (1948). 



21 References [100] and [101] appeared after the present article was completed. 

 Elraichman's paper [100] deals with an approach to the theory of turbulence (both 

 nonmagnetic and magnetic) which differs substantially from those discussed earlier 

 in the text, and is indeed contradictory to the Kolmogoroff theory. Corrsin's paper 

 [101] considers the question of local isotropy also discussed in [99]. 



{ 251 > 



