Aerodynamics of a stay cable with helical fillets - Part II: Fluctuating load and wake characteristics

Abstract

This paper presents the fluctuating load and wake characteristics of a bridge stay cable model with helical fillets in smooth flow at high Reynolds numbers. Over the Reynolds numbers tested, the frequency content of the lift coefficient in individual pressure tap rings, was dominated by low frequencies. At lower Reynolds numbers, these were caused by single separation bubble instabilities. At smaller spectral magnitudes, a vortex shedding process was observed, with a local Strouhal number dependent on the angular position of the helical fillet nearly normal to flow. For the average over the four rings, the low frequencies cancelled out, and left a high frequency vortex shedding process with a Strouhal number of 0.19 as the prominent load. The Strouhal number was maintained throughout the Reynolds number range tested. In dynamic tests, the pressure distribution was found to periodically rotate relative to the cable circumference at the natural frequency of the cable. Also, when observing the velocity components in the wake, a periodic motion of the wake synchronized with the cable motion was revealed. In static tests, the wake field instantly displaced towards the same side as the lift force generated by the asymmetric pressure distribution during boundary layer instabilities.