Analysis of flow behavior and fluid forces in large cylinder bundles by numerical simulations

This paper presents a numerical investigation of the three-dimensional flow around an in-line cylinder arrangement with up to twenty-five cylinders under confinement, with a subcritical Reynolds number, in the context of flow-induced vibrations. Flow characteristics and patterns, as well as the force coefficients of the cylinders and Strouhal numbers were evaluated numerically with the large eddy simulation approach and validated against previously published experimental data. Two values for both the transversal (T/D = 1.5 and 3) and longitudinal (L/D = 2 and 4) spacing ratios were considered and combined to generate four different arrangements. The velocity distributions obtained in the simulations were in good agreement with the experimental data. Fluctuations in the force coefficients were characterized for each arrangement and found to be directly proportional to the turbulence kinetic energy upstream of each cylinder. Depending on the flow pattern, certain rows are subjected to greater flow force fluctuations. The dominant frequency, expressed by the Strouhal number, was also mapped throughout the arrangements and its distribution was characterized according to the observed flow patterns. Although the spacing ratios have a combined effect, their separate influence on the general behavior and distribution of fluid forces could be identified, as these are linked to the flow regimes. This knowledge allowed for the contribution to an already existing in-line tube bundle classification, which is useful in the diagnosis of flow-induced vibrations and the design of heat exchangers and other industrial equipment.