Br. Lane et al., PROBABILITY-DISTRIBUTIONS AND THERMAL TRANSPORT IN A TURBULENT GRID FLOW, Physics of fluids. A, Fluid dynamics, 5(9), 1993, pp. 2255-2263
Recent theoretical proposals concerning non-Gaussian statistics of pas
sive scalars in random velocity fields are tested experimentally, by m
easuring the probability distributions of fluctuating temperature in a
n oscillating grid flow across which a steady temperature gradient is
maintained. Pronounced exponential tails occur at sufficiently high Re
ynolds number R, and predominantly Gaussian statistics at low R. When
the extended tails are present for the passive scalar, the correspondi
ng velocity power spectrum shows reasonable scaling, and the velocity
distribution is not far from Gaussian. The present paper provides a mo
re complete characterization of the flow field than an earlier brief r
eport [Phys. Rev. Lett. 67, 3507 (1991)], and also contains a descript
ion of additional features, such as the skewness of the distributions.
Finally, the effective or eddy diffusivity of both heat and a molecul
ar impurity are measured and compared.