A three dimensional CFD code is applied to the analysis of a single elastically mounted tube in cross flow. The unsteady Navier-Stokes equations are solved in a finite volume mesh with a differential Reynolds-Stress model for turbulence. The tube is supported at both ends by a spring and dashpot system in the cross-flow direction. Fluid forces, tube acceleration, tube velocity and tube displacements are computed after each time step due to the actual flow field. The results for rigid and vibrating tubes are analyzed and compared with experimental data given in the literature. Particular attention is given to the influence of vibration amplitude on the correlation length. In the conclusions the lack of models is discussed critically as well as the aspects of computation time. Suggestions are given for improvement and extension of the model to cover multiple tube rows and tube bundles.