Flow-induced transverse vibration of an elliptical cylinder with different aspect ratios

Abstract

This paper presents numerical investigations of the flow-induced vibration of an elastically mounted elliptical cylinder with different aspect ratios. The cylinder is constrained to vibrate only in the cross-flow direction, with the major axis being perpendicular to the uniform flow. The Reynolds number, based on the free stream velocity and the major axis width, is fixed as 100. The aspect ratio (AR) is based on the minor axis width over the major axis width. By specifying AR = 0.1, 0.25, 0.5, 0.75 and 1, with a fixed mass ratio of 10, the fluid–cylinder interactions are simulated using a high-order Spectral/hp element method to characterize the vibration responses, oscillation frequencies, fluctuating drag and lift coefficients, lock-in regimes and vorticity contours, with the variation of reduced velocities. A synchronization regime is found to be directly correlated with AR. For the lowest AR = 0.1, the elliptical cylinder response is found to be greater, as much as twice, than the circular cylinder response, by also exhibiting an earlier onset of the lock-in. The lack of the cylinder afterbody has a significant effect on the lower-branch response, resulting in a beating phenomenon and a rapid reduction in the response with decreasing AR. The effect of varying mass ratios is also investigated for low AR cases. The vortex shedding modes for all the response branches are found to be 2S with wake variants. A parallel vortex-shedding mode is noticed in a lower AR case with a large-amplitude oscillation whereas the C(2S) mode is observed in a higher AR case.