BRINKMAN SCREENING AND THE COVARIANCE OF THE FLUID VELOCITY IN FIXED-BEDS

The phenomenon of Brinkman screening, whereby the fluid velocity distu rbance produced by each particle in a fixed bed is attenuated by the f arces that the fluid exerts on surrounding particles, plays a crucial role in limiting the range of velocity correlations in porous media an d fixed beds. Koch and Brady [J. Fluid Mech. 154, 399 (1985)] showed t heoretically that Brinkman screening leads to a finite hydrodynamic di ffusion coefficient for fluid phase tracers in dilute fixed beds. In t his Letter, we present the results of two simulation techniques (latti ce-Boltzmann method and a multipole method) confirming the screening o f the fluid velocity covariance that underlies the Koch and Brady theo ry. (C) 1998 American Institute of Physics. [S1070-6631(98)02612-9].