AN EFFECT OF TURBULENCE ON FLUIDELASTIC INSTABILITY IN TUBE BUNDLES: A NONLINEAR ANALYSIS

Abstract

This paper is concerned with the behaviour of a tube bundle subjected to combined fluidelastic and turbulence excitation. Here, we formulate the fluidelastic forces based on a simplified, nonlinear model for a single flexible tube surrounded by rigid neighbours and constrained to move transverse to the mean flow. We use a flat power spectral density function to express the turbulence excitation. The resulting system we first examine heuristically, based on a superposition of both excitation mechanisms. We then assess the merits of this approach via direct numerical integration of the equation of motion. Lastly, we perform a nonlinear investigation into the sensitivity of the fluidelastic stability boundary on variations in the random field of turbulence and generate a stability map. The analysis shows that the fluidelastic stability boundary defined by an unstable bifurcation may be reduced by turbulence; for long-term operation, the threshold reduction may approach the size of a hysteresis region. This effect increases with turbulence intensity and decreases with unstable-limit-cycle amplitude. For a stable bifurcation, the fluidelastic stability boundary is virtually unaffected by turbulence. In the latter case, the effect of turbulence is through practical stability definitions made using amplitude–response curves.