COMPARISON BETWEEN THE SUM OF 2ND-ORDER VELOCITY STRUCTURE FUNCTIONS AND THE 2ND-ORDER TEMPERATURE STRUCTURE-FUNCTION

The previously established similarity between the temperature spectrum and the spectrum corresponding to the mean turbulent energy in a wide variety of turbulent (shear) flows is re-examined within the framewor k of second-order velocity and temperature structure functions. Measur ements in a turbulent wake indicate that D-q, the sum of the three sec ond-order velocity structure functions bears close similarity to D-the ta, the second-order temperature structure function, when D-q and D-th eta are normalized by the mean turbulent energy and temperature varian ce, respectively. This similarity also applies to other flows. In the limit of small separations, the Kolmogorov-normalized structure functi ons differ only by the value of the molecular Prandtl number. In the i nertial range, the Obukhov-Corrsin constant differs from the D-q Kolmo gorov constant by a factor equal to the dissipation time scale ratio. This ratio is typically about 0.5. (C) 1996 American Institute of Phys ics.