A new article has been published in JFS, dealing with the VIV of tandem cylidners. You can download it here: https://doi.org/10.1016/j.jfluidstructs.2019.04.006 
Fluid-Structure Interactions Lab.
Prof. F. Huera-Huarte @ Universitat Rovira i Virgili (URV)
Fluid-Structure Interactions Lab. 