Turbulence Integral Scale Corrections to Experimental Results of Aeroelastic Models with Large Geometric Scales: Application to Gust Loading Factor of a Transmission Line Tower

Abstract

Full aeroelastic model tests are often carried out to investigate the buffeting responses and the corresponding gust loading factor (GLF) of flexible structures. The geometric model scale for complicated structures may sometimes be excessively large in comparison with the ratio between turbulence integral scales measured in wind tunnel and in real atmospheric environments. This inconsistency in scale modeling leads to severe distortions of turbulence integral scale similarity whose influence manifests itself by modifications in resonant component of buffeting response and in resulting GLF as well, and numerical correction is needed when these testing results are converted to full-scale. This paper presents a correction procedure in terms of correction factors for experimental GLF obtained from full aeroelastic model tests to account for the inconsistency in scale modeling. The correction is simply made on analyzing the prototype in two air flows with different turbulence integral scales, namely the nominal value in the real atmosphere environment and the full-scale value correspondent to aeroelastic model test. The correction procedure is applied to the full aeroelastic model experiments of a transmission line tower with an unusually large geometric scale of 1/40 in order to examine the effect of turbulence integral scale on GLF. An appreciable effect is observed. It is found that the GLF obtained from wind tunnel experiments tends to be conservative for most structures and becomes unsafe for structures with extremely low modal frequencies when disregarding the correction. Correction factors are then derived to accommodate the inconsistency in modeling turbulence integral lengths. As a first generalization, a set of more general correction factors defined in terms of modal damping ratio and frequency ratio, the ratio between modal frequency and the dominant frequency in wind power spectra, are further developed through parametric analysis. The correction factors decrease with the augment of modal damping ratio and frequency ratio.