Effect of Reynolds number on the stability of a single flexible tube predicted by the quasi-steady model in tube bundles

Abstract

Fluidelastic instability is the most destructive phenomenon in steam generators and boilers. This phenomenon can be reproduced in laboratories by considering cylinder arrays subjected to cross-flow. We use the quasi-steady model to study the stability of the central tube in a parallel triangular tube bundle. The model relies strongly on the derivative of the lift coefficient to predict the onset of the negative damping mechanism and static divergence. In this work, we experimentally study the effect of the Reynolds number on the lift coefficient derivative on the central tube, for a parallel triangular array with P/D=1.5 and low Reynolds number between 20 and 700. Direct numerical simulation (DNS) results are also presented for low values of the Reynolds number, between 20 and 400, and different tube array geometries. The effect of higher Reynolds number was considered using results from the literature for Reynolds numbers in the range [2×104–2×106] and also the potential flow theory. It was found that the lift coefficient derivative strongly depends on the Reynolds number for the lower range of Reynolds number [0,1000]. Additionally, numerical methods (DNS and potential) allowed one to investigate the effect of pitch ratio and orientation of the array. The sensitivity of the lift coefficient derivative on these parameters provides some perspective on the scatter in the data found in the literature. As a result of this study, the effect of the Reynolds number on the stability of a single flexible tube is discussed. The quasi-steady model seems unable to predict the experimental results for the critical velocity, for high values of the Reynolds number.