Aerodynamic forces on a high-voltage delta-configuration lattice transmission tower segment

Abstract

This paper presents a study on aerodynamic properties of the upper segment of a high-voltage delta-configuration (cat-head) lattice transmission tower. These segments have been damaged in recent strong-wind events. A representative 1:100 scale specimen of the segment was subjected to wind tunnel tests. A computational fluid dynamics-based model was developed to simulate experimental observations. These models were extended to consider segments with different properties, and force coefficients in transverse and longitudinal directions were calculated. Further, provisions outlined in five design standards were used to estimate force coefficients for these segments. Wind forces for a segment can be determined by multiplying that computed using ASCE 74 or IEC 60826 by a factor, which is a function of yaw angle and solidity ratio. This factor varies between 1.0 and 1.6 (1.0 and 2.0) for the transverse (longitudinal) direction. Additional analyses revealed that an approximately 100% increase in the gap between adjacent longitudinal faces leads to an approximately 10% increase in the force coefficient, and that the influence of Reynolds number and turbulence parameters is small. Further, introduction of cross-arm led to a less than 10% reduction in the force coefficient for transverse direction; the influence was negligible in the longitudinal direction.