Wake dynamics past a curved body of circular cross-section under forced cross-flow vibration

• Published in: Journal of fluids and structures 2009-05, Vol.25 (4), p.721-730
• Main Authors: de Vecchi, A., Sherwin, S.J., Graham, J.M.R.
• Format: Article
• Language: English
• Subjects: Curved bluff body; Exact sciences and technology; Fluid dynamics; Forced vibration; Fundamental areas of phenomenology (including applications); Physics; Rotational flow and vorticity; Solid mechanics; Structural and continuum mechanics; Turbulent flows, convection, and heat transfer; Vibration, mechanical wave, dynamic stability (aeroelasticity, vibration control...); Vortex shedding; Wakes
• ISSN: 0889-9746; 1095-8622
• DOI: 10.1016/j.jfluidstructs.2009.01.005

Three-dimensional numerical simulations are presented of flow past a curved body at a Reynolds number of 100. The geometry consists of a circular cross-sectioned body, whose centreline axis is prescribed by a quarter ring with a horizontal extension. This plane of curvature of the body is aligned to the free-stream flow direction such that the outer part of the ring is the body's stagnation face (convex configuration). The bluff body is forced to sinusoidally vibrate in the cross-flow direction at different amplitudes and frequencies. The resulting vortex shedding is strongly influenced by the curvature of the body. Within the lock-in region for a straight cylinder, the shedding past the convex body exhibits a 2S mode for all the pairs of input parameters tested; outside this region, a “weak” form of shedding with two pairs of counter-rotating vortices per cycle occurs in the top part of the body. At lower amplitudes of oscillation and frequencies below the Strouhal value for a straight cylinder, dislocations are found in the near wake: these generally occur in the middle of the curved part of the body, at an angle of approximately 45 ∘ from the top plane, regardless of the amplitude of oscillation. However, at very low amplitudes, an increase in the input frequency is found to influence the spanwise position of the dislocations by shifting them towards the top sections. The wake dynamics and force distribution are associated with the relative importance of the different regions of the curved geometry: the top region, nearly perpendicular to the inflow and therefore comparable to a straight cylinder, and the lower region with the horizontal extension, which is parallel to the inflow direction and hence behaves similarly to a slender body. The influence of the force contributions from these regions and their different nature determine the occurrence of dislocations in the wake, as well as their position along the span. The energy transfer mechanism, which determines whether the body is excited or damped by the flow, is also affected by this balance: at very low amplitudes the top part undergoes a lift force due to vortex shedding, which is strong enough to overcome the dampening effect from the horizontal extension used in this case and therefore provides a positive energy transfer from the fluid to the structure.