Multiscale Dynamics in Turbulent Wakes

In this work we demonstrate the energy exchange processes to/from coherent structures present in a multiscale flow consisting of a main cylinder and a control rod. Apart from the vortex shedding frequencies of the two wake-generating bodies, new frequencies are observed that correspond to the sum and difference of the former. We show that the sheddings of the wake-generating bodies are energised by the mean flow, hence we refer to them as ‘primary modes’. Contrastingly, the new frequencies are found to be entirely energised through non-linear interaction between the primary modes, establishing the notion of ‘secondary modes’ that are not directly energised by the mean flow. The same analysis is extended for a wind turbine wake which is inherently of multiscale nature. Preliminary results show that there not only exist modes that resemble the primary and secondary modes observed in the prior cylinder–control rod flow, but there also exist modes of mixed nature (energised by both mean flow and non-linear interactions) and modes that are solely driven by convection.