A Computational Study on the Damping-Amplitude Dependence and Estimation of the Limit Cycle Oscillations for Normal Triangular Arrays with One Tube Undergoing Fluidelastic Instability

Abstract

While the estimation of the critical velocity for fluidelastic instability of tube arrays has received considerable attention for decades, the studies intended to analyze the post-stable behavior have been scarce. However, the behavior of the system under instability, is also interesting in order to characterize the amount of energy transferred from fluid to structure. A computational study has been carried out for the case of one tube vibrating in a normal triangular array by means of a CFD model previously developed with Fluent by the authors. This model incorporates the motion of the vibrating tube by means of user defined functions for both forced and free oscillations, so that the tube position can be updated and the mesh rebuilt at every time step. First, predictions of limit-cycle oscillations (zero net damping) were obtained for pitch ratios P/d = 1.25 and 1.375, so that the experimental response curves (amplitude against flow velocity) measured in other experimental studies could be used for contrast purposes. After validation, the CFD model was used to investigate how the net damping of the fluid-structure system depends on the vibration amplitude for a given flow velocity, which shows the non-linear nature of the tube response. Finally, special simulation series were conducted to explore the effects of pitch ratio, Reynolds number and structural damping on the net damping of the system for constant vibration amplitude.