The concentration of pulp fibers in three-dimensional fully developed turbulent channel flow is investigated by two numerical methods: a random-walk simulation and large eddy simulation (LES). For the random-walk simulation, the Reynolds averaged Navier-Stokes equations are solved for the mean flow fields with Reynolds number 65,000 (based on average channel velocity and channel half-width). The individual components of the fluctuation velocities are obtained by curve-fitting existing experimental data for the whole channel width. The LES is performed at Reynolds number Re, (based on friction velocity and channel half-width) of 2820, which is close to the flow condition used for the random-walk simulation. A flexible fiber model is used to simulate the fiber motion. A general wall model is developed to deal with the fiber interaction with the walls. Both simulated results show that the concentration increases linearly near the wall and becomes approximately constant farther from the wall, in reasonable agreement with experimental observations. (C) 2002 Elsevier Science Ltd. All rights reserved.