A few statistical properties of fine-scale velocity and temperature fluctuations have been measured on the axis of symmetry of a heated turbulent round jet. The probability density of ∂θ/∂x, the streamwise derivative of the temperature fluctuation, is strongly negatively skewed, indicating a lack of isotropy for the fine-scale temperature structure. An estimate of the correlation between the velocity and temperature dissipation fields has been obtained by assuming that the dissipation of velocity and dissipation of temperature can be approximated by (∂θ/∂x)2, whereuis the streamwise velocity fluctuation, and (∂θ/∂x)2rrespectively. The correlation between the quantities (∂θ/∂x)2rand (∂θ/∂x)2raverages over a volume of linear dimensionr, is fairly high and depends on the choice ofr.An analysis shows that this correlation plays a vital role in the prediction of high-order structure functions ofuand θ. The assumed lognormality of the probability density of (∂θ/∂x)2rand (∂θ/∂x)2rand of their joint density is found to be reasonable over a range ofrcorresponding to the inertial subrange.
Fine-Scale Temperature Fluctuations in the Orion Nebula and thet2Problem
