Numerical Computation of Modal Characteristics of a Clamped-Clamped Cylinder in Turbulent Axial Pipe Flow

In this paper the modal characteristics of a flexible cylinder in turbulent axial flow are investigated with partitioned fluid-structure interaction simulations. In these simulations a computational fluid dynamics calculation to resolve the flow field is coupled with a computational structure mechanics calculation to compute the structural behavior. The cylinder is initially deformed according to an eigenmode in vacuo and then released. From this free vibration decay of the cylinder in the turbulent axial flow, modal characteristics are determined. To assess the accuracy of these calculations, the same configuration is computed as in an experiment with a solid brass cylinder mounted in a water-conveying pipe. The natural frequency appears to be relatively insensitive to an increase in flow velocity in this case. Both experiments and computations show the same trend of slightly decreasing natural frequency with increasing flow velocity. The damping, on the other hand, is very sensitive to the flow velocity. A change in flow velocity from 10m/s to 30 m/s results in a modal damping increase from 1.4% to 3.0%. Changes in molecular viscosity due to temperature differences had only a small effect on modal damping.