Abstract

The buoyancy effects on the turbulence structure in unstably-stratified shear flow generated by cooling the top of the layer in an open channel were investigated. Measurements were made of the characteristics of the turbulent fluctuations; turbulence intensities, correlation coefficients, joint probability density functions, and coherence-phase relationships. The results show that the buoyancy-driven motions cause substantial changes in the turbulence structure. Of the buoyancy-driven motions, the intermittent downward motion contributes mainly to the turbulent transport of heat in the vertical direction. A parameter which characterizes the stability dependence of the turbulence structure is the local gradient Richardson number Ri, and the turbulence quantities are well correlated with Ri. A theoretical spectral equation model is applied to the stratified flow and well compared with the experimental results.

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