Energy contents and vortex dynamics in Mode-C transition of wired-cylinder wake

Abstract

The 3D transition of the flow behind a circular cylinder with a near-wake wire disturbance has been investigated experimentally. The flow is oriented horizontally and the wire is positioned in the upper half of the wake. We performed flow visualization and particle image velocimetry experiments to investigate the influence of the wire on various properties of the flow, such as the dynamics of the spanwise structures. Experiments were performed in the Reynolds number range of Re = 165–300. It is shown that in Mode-C transition of the wired cylinder wake, some part of the streamwise vorticity content of the upper von Kármán vortices located at the perturbed side, is transferred to the secondary vortices. This vorticity transfer results in upper von Kármán vortices which are weaker than the lower ones. The analysis of the discrete energy content of the wake supports this analysis by showing that the energy intensity at von Kármán vortex shedding frequency f0 at the perturbed side of the wake is less than the energy intensity in the lower half. This leads to conclusion that the excess energy is transferred to the subharmonic frequency f1 ≈ f0/2.

Two- and three-dimensional instabilities in the wake of a circular cylinder near a moving wall

“…The λ C values obtained in the present case are similar to those reported in the literature, e.g. λ C = 1.8D and 2.2D for flow past a circular cylinder with a trip-wire in the near wake by Zhang et al (1995) and Yildirim et al (2013b), respectively, and λ C ~ 1.7D for flow past a circular ring (Sheard et al, 2003).…”

Three-dimensional wake transition of a diamond-shaped cylinder

“…The most unstable spanwise wavelength for the subharmonic mode (∼1.9h) is similar to the wavelengths for the subharmonic mode observed in the wake of other bluff bodies (e.g. Sheard et al 2009;Yildirim, Rindt & van Steenhoven 2013).…”

Mode C flow transition behind a circular cylinder with a near-wake wire disturbance

“…symmetry-breaking effect of the wire compared to the natural transition modes A and B, and to show the development of the streamwise vortices as a function of time. As indicated above, the secondary streamwise vortices in mode C transition originate from the primary upper vortices only, resulting in the typical 2T-periodic nature of mode C. The energy transfer from the primary to the secondary vortices is analysed in detail elsewhere (see Yildirim, Rindt & van Steenhoven 2013). The origin of the instability for the natural transition modes A and B arises from an elliptic instability of the vortex cores for mode A and from a hyperbolic instability in the braid region for mode B (Williamson 1992(Williamson , 1996aLeweke & Williamson 1998;Thompson et al 2001).…”