A study on the energy transfer of a square prism under fluid-elastic galloping

Abstract

In this paper, power transfer of an elastically mounted body under the influence of fluid-elastic galloping is analysed.The quasi-steady state model equations are first analysed to find suitable governing parameters. It is shown that, as well as Re, the system is a function of three dimensionless groups: a combined mass-stiffness parameter, Π1; a combined mass-damping parameter, Π2; and mass ratio, m⁎.Data obtained by numerically integrating the quasi-steady state equations show that for high values of Π1, the power extracted from the flow is a function of Π2 only. For low values of Π1, the power extracted is still a strong function of Π2, but is also a weak function of Π1. For all the cases tested, the power extracted was independent of the value of m⁎.These results are then compared to results of direct numerical simulations. It is found that Π1 has a much stronger impact on the power extracted than predicted by the quasi-steady state model. The error is shown to be an inverse function of Π1. The failure of the quasi-steady state model at low Π1 is hypothesised to be due to the stronger influence of vortex shedding, which is not accounted for in the quasi-steady model. Spectral analysis of the DNS cases at low Π1 shows a significant response at the vortex shedding frequency. The strength of the vortex shedding response is also shown to be an inverse function of Π1.Even though the quasi-steady state model does not accurately predict the power extracted, it does predict the parameter values at which maximum power transfer occurs reasonably well, and both the quasi-steady model and the direct numerical simulations show that this value is basically independent of Π1.