RESUMO
Higher-order passive scalar (temperature) structure functions are measured in the turbulent wake of a circular cylinder at a Taylor-microscale Reynolds number (Rlambda) of 370. The scalar is injected by two different means: (i) heating of the cylinder and (ii) use of a mandoline. Even though the second-order statistics (e.g., power spectra, second-order structure functions) of the scalar field are experimentally indistinguishable in the inertial and dissipative ranges, we observe notable differences in the inertial-range scaling exponents (xin) of the scalar structure functions at higher orders. The implication is therefore that the variations in previous estimates of xin may be attributable to differences in the scalar field initial conditions (and may not be deemed characteristic of a universal nature of the small-scale statistics of turbulent passive scalars).
RESUMO
A generalized form of Yaglom's equation, in which the effect of turbulent production of temperature fluctuations is taken into account, is derived. The modified Yaglom equation (which extends the work of Danaila et al. [J. Fluid Mech. 391, 359 (1999)] to incorporate the effects of decay and production) is compared with experimental data. The flow under consideration is decaying grid turbulence with an imposed mean temperature gradient (Mydlarski and Warhaft [J. Fluid Mech. 358, 135 (1998)]). The agreement between theory and experiment is good and the effects of nonhomogeneities in the flow are small.