Abstract:
The work reported in this thesis includes the
development of a device, based on the method of electro
magnetic induction, for measuring turbulent velocity
fluctuations in water. This method for turbulence measure
ments in water was first used by Grossman (26) and later
studied by Day (14) and Gratz (25) at the University of
Wisconsin, where the experimental work reported here was
carried out. In the present work, the r.m.s, value of
u« fluctuations as well as their spectra were measured.
These measurements were made in a 2"dia. Incite pipe along
a diameter for proving of the equipment. Studies were then
conducted of the decay and energy spectra downstream of
various grids - singly as well as in combination.
The linear decay law, based on Kolmogoroff's
hypothesis has not been found to be adequate to describe
the decay behind a grid. Also it was found that a change
in initial conditions brought about a change in the decay
law as well. This can be attributed to the fact that the
similarity of spectrum of energy does not hold good over
a very wide range of wavenumbers. This deviation from
similarity was also experimentally verified.'
A generalised theory of similarity of spectra
and decay law was proposed by Goldstein, wherein account
was taken of the effect of Reynold's numbers and the
initial conditions on the law of decay as well as on
similarity of spectra. The postulates of this theory
have been confirmed with the experimental data obtained,
in as much as the results can be explained on the basis
of the above theory.
