Refinement of the Correlation Length Method for Predicting Vortex-Induced Vibrations in Slender Structures

Vortex-induced vibrations (VIV) are a major design concern for slender towers, chimneys, and wind-turbine structures. The effective correlation-length method, adopted in current design standards such as Eurocode 1, remains widely used but has not been comprehensively validated across the full parameter space relevant to modern lightweight structures. This study presents new experimental results obtained in the boundary-layer wind tunnel of RWTH Aachen using the forced-oscillation method. The experiments quantify the influence of structural slenderness, oscillation amplitude, and atmospheric boundary-layer turbulence on the correlation length governing cross-wind response. Two rigid aluminium models with different slenderness ratios were tested under smooth and turbulent flow conditions representative of terrain categories I–IV. To complement these measurements and validate the aerodynamic excitation obtained from the forced-vibration approach, additional aeroelastic tests were conducted using lightweight carbon-fibre tube models capable of reproducing self-excited vibration behaviour under resonance. The combined results confirm the consistency of both testing approaches and provide insight into the dynamic coupling between flow and structure. Measured correlation lengths generally exceed current standard values, particularly under turbulent flow and higher oscillation amplitudes, indicating that existing design provisions may underestimate aerodynamic excitation. The findings support a refined formulation of the correlation-length-based VIV model, improving its applicability to modern tall and flexible structures and enabling more reliable fatigue and serviceability assessments.