Kinetic energy budgets of triple-components in a cylinder wake

Abstract

The velocity fields of wakes after a cylinder were disintegrated using a conventional triple decomposition method to investigate the kinetic energy transfer mechanism among the mean flow, unsteady wave, and turbulence. Two-dimensional and two-component (2D-2C) velocity fields were measured using particle image velocimetry (PIV) in a rectangular cross-section water tunnel. For analysis, the proper orthogonal decomposition (POD) was applied to the velocity fields, and it was found that the combination of its first two modes constructs the unsteady coherent motion – in other words, wavelike motion within the cylinder wake. The investigation of the kinetic energy budget also revealed that the dissipation in the regime of coherent motion is negligible, as it is in wave propagation, unlike in the regime of turbulence. Furthermore, the turbulence energy produced by coherent waves was significantly smaller than the wave or turbulence energy directly produced by mean flow. Lastly, in conjunction with the kinetic energy budget, the momentum equation can explain the large deformations of mean velocity in more detail. As a result, the importance of negative production and energy transport has been highlighted.