On the correlation between temperature and velocity dissipation fields in a heated turbulent jet

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 , where u is the streamwise velocity fluctuation, and (∂θ/∂ x ) 2 r respectively. The correlation between the quantities (∂θ/∂ x ) 2 r and (∂θ/∂ x ) 2 r averages over a volume of linear dimension r , is fairly high and depends on the choice of r. An analysis shows that this correlation plays a vital role in the prediction of high-order structure functions of u and θ. The assumed lognormality of the probability density of (∂θ/∂ x ) 2 r and (∂θ/∂ x ) 2 r and of their joint density is found to be reasonable over a range of r corresponding to the inertial subrange.