An experiment on turbulence in a density-stratified fluid, incorporating experimental results for isothermal and non-isothermal, turbulent flow in a channel

Turbulent shear flows with an imposed density-stratification have been studied, for the most part, in atmospheric and oceanic field situations. Deduction of the basic dynamics of flows with density-stratification has been based on studies of this type with little appeal to laboratory experiments; the number of suitable laboratory experiments that have been performed has been limited by both the large and costly experimental rigs required and the lack of adequate instrumentation techniques. However, it is believed by the author that a sound understanding of the underlying dynamics of turbulent shear flows with an imposed density-stratification should be a preliminary step in the study of the several naturally occurring flows of this type and also the flows met with in engineering practice in which density-stratification may have a significant role. The flow in a two-dimensional channel was preferred to boundary layer flow for study owing to the known flux profiles, the constrained turbulent scale and the lack of turbulent intermittency of the former. [...]
The results also suggest the existence of a critical Richardson flux number both as a local parameter and as a gross parameter. The density-stratification markedly suppress the transfer of turbulent kinetic energy from the longitudinal velocity component to the vertical velocity component. These results suggest the existence of a second critical Richardson flux number which may not be equal to the first. Comments are mad concerning the correctness of some of the modelling techniques used to describe turbulent shear flows in a density-stratified fluid. Finally suggestions are given for continuation of the work presented in this thesis.