Vortex-induced vibrations of an elliptic cylinder with both transverse and rotational degrees of freedom

Autor: Huakun Wang, Kaixiao Chen, Qiu Zhai
Rok vydání: 2019
Předmět:
Zdroj: Journal of Fluids and Structures. 84:36-55
ISSN: 0889-9746
DOI: 10.1016/j.jfluidstructs.2018.10.004
Popis: Two-degree-of-freedom (2-DOF) vortex-induced vibration (VIV) of an elliptic cylinder is numerically investigated at a Reynolds number R e = 150 . The incompressible Navier–Stokes equations in arbitrary Lagrangian–Eulerian formulation are solved by a four-step fractional finite element method. The elliptic cylinder, with a variety of aspect ratios (AR = 1.0–2.5), is free to vibrate in both transverse and azimuthal directions. At each AR, the computations are conducted within a wide range of reduced velocities (2 ≤ U r ≤ 15). For comparison, the one-degree-of-freedom (1-DOF) responses of the cylinder vibrating only transversely are also provided. The results show that significant rotations occur under a condition of frequency synchronization similar to the lock-in condition of VIV in the transverse direction. Under the rotation effect, the transverse peak amplitude at AR = 1.0 reaches a higher value about 20% larger than its counterpart of 1-DOF VIV, whereas it fells by more than half at AR = 2.0 and 2.5, and the corresponding wake patterns present distinct characteristics. The typical phenomenon of phase switch can be captured successfully between the torque and rotation response, which occurs at the same reduced velocity to the phasing between the transverse force and motion. Our simulation results also elucidate that the free rotation may significantly affect the statistics of the drag, lift and moment coefficients. The most striking observation is that all of the force responses at AR = 2.0 and 2.5 collapse onto a very low level compared to those of the transverse-only VIV. This is consistent with the dramatic drop in the transverse vibration amplitude at the same AR.
Databáze: OpenAIRE
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