This publication draws on the work carried out during an IAEA coordinated research project to benchmark computational fluid dynamics (CFD) codes used in fuel assembly design and model options and methods against ‘CFD quality’ experimental data under single phase flow conditions. It presents the results obtained by seven participating institutes from six Member States, all with currently operating water cooled reactors. The publication provides a description of the omni flow experimental loop test facility used for benchmark experiments related to the phenomena of fuel assembly spacer grid induced flow mixing. The focus of the benchmark was on the downstream region after the spacer grid. The comparisons between the experimental measurements and the CFD calculations are hence focused on the average velocity, the fluctuating velocity (turbulence), and local cladding temperatures in this region.