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.