One of the key issues in membrane technology is to avoid fouling which is formed on the membrane surface. To get over this trouble, the use of a patterned surface was suggested as a way to reduce fouling. In this report, both the experimental and numerical studies were performed with a prism patterned membrane system. In our experiments, we observe the local distribution of microbials; more fouling in the lower part of the pattern and less fouling in the upper region. In the simulation, the vortex develops in the lower part of the pattern, in which the aggregates of solid components in the sludge can be easily formed, leading to a favorable fouling formation. It is also observed that the local wall shear stress is higher in the upper region of the pattern compared to the lower region where the vortex is formed. High shear stress facilitates detachment and prohibits attachment of solid components on the membrane surface. The simulation result (vortex formation in the lower region of the pattern and higher stress in the upper region) is in accordance with the experimental results on the distribution of microbials in the patterned membrane system (more fouling in the lower part of the pattern, and less fouling in the upper region). This indicates the importance of flow characteristics as well as the stress distribution to reduce the fouling in the patterned membrane system. In addition, it is emphasized that the pattern should be designed efficiently by considering the local flow and stress distribution in the cross flow membrane system. (C) 2012 Elsevier B.V. All rights reserved.