Ebook: Decay of weak turbulence

The Catholic University of America, 1969. 70 p.A detailed experimental investigation of the structure of weak turbulence generated by various single and multiple-stage grids has been made. The weak turbulent fields were limited to those having no interaction with the mean flow field. The present study covers a range of Reynolds numbers of turbulence between 70 and
7. Components of turbulence were found to have equipartition of energy
in the final stage of decay. When the Reynolds number of turbulence is 30, the kinetic energy of turbulence decreases inversely as the square of decay time. All the length scales of turbulence increase as the square root of time, while the Reynolds number of turbulence decreases as the square root of time. The longitudinal correlation function is closer to a Cauchy's distribution than a Gaussian distribution function. The resultant three-dimensional energy spectrum show continuous transfer of energy from the low to high wave numbers through out the final stage of decay. The measured time-correlation functions up to the fourth order indicate that the grid-generated turbulence is not completely consistent with normal statistics. All experimental evidences imply that in the final stage of decay the wave components of turbulence are not completely independent with unlimited degrees of freedom but are closely related to the kinetic model of a field consisting of a specific type of line vortices which are aged and essentially non-interacting.