PROBABILITY-DISTRIBUTIONS AND THERMAL TRANSPORT IN A TURBULENT GRID FLOW

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.