Experiments in nearly homogeneous turbulent shear flow with a uniform mean temperature gradient. Part 2. The fine structure

Abstract

Previous measurements in nearly homogeneous sheared turbulence with a uniform mean temperature gradient are here supplemented with data on the fine structure of the velocity and temperature fluctuation fields. The statistics of signal derivatives and of band-passed signals show that neither field is locally isotropic in the spectral range covered, possibly because of the insufficiently large turbulent Reynolds and Péclet numbers. Observed skewnesses of both velocity and temperature derivatives are explained qualitatively with the use of a kind of ‘mixing-length’ model. The flatness factors of the derivatives and of band-passed, high-frequency signals indicate appreciable departures from normality, consistent with the spatially ‘spotty’ fine structure. The temperature flatnesses are a bit larger than those of the streamwise velocity. The homogeneous shear flow data are compatible with measurements in turbulent boundary layers at comparable RΛ and PΛθ.