Vortex-induced vibration of a cooled circular cylinder

We numerically investigate vortex-induced vibration of a cooled circular cylinder in the presence of thermal buoyancy. We employ an in-house fluid-structure interaction solver based on a sharp-interface immersed boundary method. The cylinder is elastically mounted and is free to vibrate transversely to the flow direction. The surface of the cylinder is prescribed at a temperature lower than that of the fluid, and the gravity is aligned opposite to the flow direction. Numerical simulations are carried out for the following parameters: Reynolds number, Re = 150, Prandtl number, Pr = 7.1, Richardson number, Ri = [−1, 0], mass ratio, m = 2, and reduced velocity, UR = [3, 20]. The oscillation amplitude of the cylinder is larger in the presence of the thermal buoyancy for 4 < UR < 15. The amplitude is maximum at UR = 11 and is around ≈1D* in the presence of the thermal buoyancy, where D* is the diameter of the cylinder. However, this amplitude is ≈0.6D* at UR = 4 in the absence of the thermal buoyancy. The lock-in (synchronization) region is obtained for a wider range of UR in the presence of the thermal buoyancy. In the presence of the thermal buoyancy, along with a dominating vortex shedding frequency, we obtain multiple weak as well as strong even and odd harmonics along with subharmonics of the fundamental frequency in the lift signal. However, the secondary frequencies are limited to only a weak third harmonic of the fundamental frequency in the absence of the thermal buoyancy. We observe elongated as well as wider vortices and isotherms in the presence of the thermal buoyancy although the vortex shedding mode remains “2S.” Our results show that there exists a critical minimum absolute value of Ri in order to achieve the lock-in and this value increases with UR.