An experimental study on dynamic ice accretion and its effects on the aerodynamic characteristics of stay cables with and without helical fillets

An experimental investigation was conducted to examine the effects of helical fillets on dynamic ice accretion process over the surfaces of bridge stay cables and evaluate its effects on the aerodynamic characteristics of the stay cables under both dry rime and wet glaze icing conditions. The experimental study was performed in the Icing Research Tunnel of Iowa State University (i.e., ISU-IRT). Four bridge stay cable models, including a standard plain cable model and three helical filleted cable models of different helical pitch lengths, were used for the experimental investigation. During the experiment, in addition to using a high-speed imaging system to record the dynamic ice accretion process over the cable surfaces, a Digital Image Projection (DIP) based 3D scanning system was also utilized to quantify the 3D shapes of the ice structures accreted on the test models. While a high-resolution digital Particle Image Velocimetry (PIV) system was used to characterize the wake flows behind the cable models during the ice accreting process, the time variations of the aerodynamic drag forces acting on the test models were also measured by using a pair of force/moment transducers mounted at two ends of the cable models. It was found that, under the rime icing condition, the helical filleted cable models accreted more ice structures than the standard plain cable model. However, the helical filleted cable models were found to have less ice accretion under the wet glaze icing condition. The pitch length of the helical fillets was also found to affect the ice accretion process substantially. Under the rime icing condition, while the aerodynamic drag forces acting on the cable models were found to decrease continuously with more rime ice accreting over the cable surfaces, the drag reduction due to the rime ice accretion was found to be less obvious for the helical filleted cable models, in comparison with that obtained for the standard plain cable model. Under the glaze icing condition, the aerodynamic drag forces acting on the cable models were found to decrease quickly at the initial stage of the glaze icing process, and then increase gradually with the increasing ice accretion time at the later stage of the ice accreting process. PIV flow field measurements were correlated with the force measurement data to elucidate the underlying physics for a better understanding of the variation characteristics of the aerodynamic forces acting on the cable models under different icing conditions.