Numerical Study of Tube Array Vibrations Under Cross Flow

Tube array vibration in heat exchangers has been treated thoroughly. One part of the vibration is induced by the cross flow. The vibration of a free tube, surrounded by rigid tubes, is a common model used to simplify the problem. In this paper, a numerical simulation of this experiment is carried out and a database of the results is created. Some assumptions have been introduced in the simulation. The flow is considered incompressible, monophasic and non-turbulent. The tubes are fixed, except for the central one, which has a mass, a damping ratio and a frequency in vacuum. At the initial time, it is displaced from its static equilibrium. Variables of the simulation include the parameters of the tube in vacuum, the water velocity, the separation between tubes and their diameters. The results are the frequency and the damping ratio that enable the characterization of the the dimensionless mass-damping parameter. Many results have been collected, by changing these parameters. The results include a Rogers’ formula review. This formula is used to obtain the mass and damping factor from the tubes’ diameter-pitch ratio, when there is no flow. In this manuscript the influence of the water velocity on those factors is explained. When water velocity grows, the damping ratio of the central tube becomes negative, therefore, the tube becomes instable. Increasing the velocity further makes this instability disappear, generating a new zone of stability. This initial instability is compared to other authors experimental results.