Temporal evolution of lift in a pure cruciform system for energy harvesting

Abstract

We investigated the displacement and lift time series of a circular cylinder - strip plate cruciform system for energy harvesting in the Reynolds number range 1.1×103=Re=14.6×103, numerically using the open source C++ library: OpenFOAM. The Karman vortex-induced vibration (KVIV) regime was identified between reduced velocity, U*, 2.3 and 13.6, while the streamwise vortex-induced vibration (SVIV) regime was identified between 18.2=U*=29.5. We analysed the cylinder displacement and lift time series using the Hilbert-Huang transform (HHT). Within this range of U*, Karman vortex shedding contributes nearly as much as streamwise vortex shedding to the root-mean-square amplitude of total lift, while between 25.0=U*=29.5, the Karman component contribution is on average twice that of the streamwise component. These findings hint at the possibility to improve the power output of the harvester by a factor of two between 18.2=U*=22.7 and by a factor of three between 25.0=U*=29.5, if we can unite the contribution to the root-mean-square amplitude of the total lift under a single vibration-driving mechanism: the shedding of streamwise vortex.