Helical strakes on High Mast Lighting Towers and their effect on vortex shedding lock-in
An experimental study on the effect of helical strakes on vortex induced vibrations and the lock-in phenomenon in High Mast Lighting Towers (HMLTs) is investigated. Two multi-sided tapered scaled models are clamped in place in a subsonic wind tunnel that is equipped with a hot-wire sensor and a traverse mechanism. The shedding frequency data is collected for the models with and without helically patterned strakes with the use of two different ropes. The responses of the tower models, for a Reynolds number of 44, 000, are compared and discussed under different configurations including: two directions of the model with respect to the direction of the flow, and changes in the ratio of strake height to HMLT diameter. Four major aspects of the spectrum of the hot-wire signal from the wake are studied: the vortex shedding frequency, signal strength, characteristic spectral peak area, and characteristic spectral peak width. It is observed that, for most cases, no specific method produces a decisive outcome. However, some of the results for the 12-sided model provide supporting evidence that the vortex induced vibrations may be mitigated with the use of helical strakes.^
Steven H. Collicott, Purdue University.