Numerical investigation of the vortex-induced vibration of an elliptic cylinder free-to-rotate about its center

Vortex-induced vibration (VIV) of an elliptic cylinder free to rotate about its center is numerical studied at Reynolds number 2580≤Re≤15490. The vibration and rotation responses occurring simultaneously are considered with normalized torsional friction varied from 3.34×10⁻⁴ to 1.17. A two-way fluid–structure interaction (FSI) approach is used to solve the incompressible flow equations and the structure motion including the vibration and rotation in two dimensions. The numerical results indicate that the torsional friction is a key factor, determining the rotation response and then affecting the vibration amplitude. When the torsional friction is too large or the reduced velocity is too small, the elliptic cylinder is unable to rotate, while too small friction leads to transverse galloping instead of the desynchronized region. For the elliptic cylinder with moderate frictions, the response occurs similar as the circular cylinder, but the amplitude in the desynchronized region is larger than the circular cylinder due to the hydrodynamic instability. The results show four kinds of rotation response, which are associated with the time-averaged torque and the flow field around the elliptic cylinder. Compared to the non-rotatable elliptic cylinder with 0° attack angle, the rotatable cylinder vibrates more vigorously.