Turbulent flow over a rough wall with suction or blowing is a common fluid mechanics problem that has many practical applications including pulp screening. To better understand, the complex hydrodynamics at the critical region near the surface of the wall, the streamwise mean and velocity fluctuations were determined experimentally using laser Doppler velocietry. The near-wall streamwise velocity fluctuations and local mean streamwise velocity were shown to be a strong function of the surface roughness, and the aperture and cross-flow velocities. A correlation for the mean velocity and the wall shear stress acting near the wall was determined. (C) 2008 American Institute of Chemical Engineers.