STUDY OF LIQUID TURBULENCE SPECTRA BEHIND GRIDS USING ELECTROMAGNETIC INDUCTION

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.