UNIFORM MEAN SCALAR GRADIENT IN GRID TURBULENCE - ASYMPTOTIC PROBABILITY-DISTRIBUTION OF A PASSIVE SCALAR

An asymptotic self-similar solution is obtained for the one-point prob ability density function (pdf) equation, of a passive scalar with unif orm mean gradient in incompressible homogeneous turbulence. It is argu ed that the same solution should be a valid approximation when turbule nce is generated in a high-quality wind tunnel. The asymptotic pdf sha pe is a unique function of the conditional expectation of the normaliz ed scalar dissipation rate. The mean scalar gradient modifies the scal ar pdf shape only if the conditional expected velocity component in th e direction of the mean gradient is a nonlinear function of scalar flu ctuation value. Experimental data from wind tunnel studies are consist ent with the sign and scale of the changes produced by these nonlinear ities. (C) 1996 American Institute of Physics.