Some Basic Laws of Isotropic Turbulent Flow Page: 3 of 37
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NACA TM No. 1079
and has enabled Taylor to develop the theory of the dissipa-
tion of turbulent disturbances behind screens and enabled Von
Kirmin to give a general equation for turbulence propagation.
The concept of association moment makes it possible to
determine such an important magnitude as the "scale of the
turbulence," a characteristic of turbulence of equal impor-
tance with the other characteristics; namely, the amplitudes
and frequencies of the fluctuations. Modern physical experi-
ments, such as are conducted in aerodynamics, permit measuring
the association moments and thus check the results of the
theory. From the practical point of view new theories are
.important because they replace semiempirical theories, they
throw light on the physical structure of turbulent motion,
and also because they provide a firm basis for the investiga-
tion of artificial flows in-aerodynamic wind tunnels;-open
channels, and so forth. A knowledge of the turbulence charac--
teristice of these flows permits a more accurate estimate of
the scale effects of the phenomena and better application of
the modeltests to full-scale design.,
A furthet development of the'problem of the diffusion of
artificially produced turbulence behind screens or other tur-
bulence-producing devices is presented in this paper. With
the fundamental assumptions of the theory more accurately de-
fined a method is proposed that permits the investigation of
the diffusion of turbulent disturbances of finite scale in
place of the point source disturbances considered by Von
Karman. The method is based on the author's concept of "mo-
ment of'disturbance" as a certain theoretically well-founded
measure of turbulent disturbances. Incidentally, with- the
object of fatiliarizing the reader.with the fundamentals pf
the new theory, the latter is'presented in'a form" hat is con-
sidered simpler than that given in existing liter'tuve.
a , L
1. HOMOGENEOUS AND ISOTROPIC TURBULENCE - ASSOCIATION
MOMENTS AND 0OQRELATION TENSOR - TWOFIRST:CORRELATION
FUNCTIONS YO MOHENTS OF THE SEQOND'ORDER
Visualize a homogeneous turbulent flow, that is, a flow
at a given instant the average charabtbrietics of which are
the same at different points. Take an. two points in the flow
M and M' Snd .denote their relative radius vector . by z
and its projections on" the coordinatp'axes bj 1,. a, is*
The flow velocities at points K &nd H" at the same instant
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Loitsianskii, L. G. Some Basic Laws of Isotropic Turbulent Flow, report, September 1945; (digital.library.unt.edu/ark:/67531/metadc63978/m1/3/: accessed November 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.