Hydrodynamic and heat transfer characteristics of two circular cylinders in series under two-degrees-of-freedom vortex-induced vibration

The heat transfer and hydrodynamic properties of two rigid cylinders in series with fluid disturbance at the laminar flow under vortex-induced vibration were studied numerically. The six DOF model was chosen and combined with user-defined functions (UDF) to seek a solution for the cylindrical equations of motion. The coupled calculation between fluid flow and rigid body motion was realized by combining the dynamic mesh technique. The effects of two types of motion conditions of the upstream cylinder, i.e. fixed (referred to as model A) and with two degrees-of-freedom (referred to as model B), on the flow field and heat transfer of the downstream cylinder with two degrees-of-freedom were investigated. The numerical results showed that in the reduced velocity (Ur) range considered in this work, the heat transfer and motion conditions of the downstream cylinder were subjected to the self-shedding vortices and the shedding vortices of the upstream cylinder. The comparison of models A and B at Ur = 4 and Ur = 5, respectively, displayed that the force frequency of the downstream cylinder was close to the natural frequency when it was impacted by the tail vortices shedding of the upstream cylinder and the self-shedding vortices. This resulted in the maximum transverse amplitude and strongest heat transfer of the downstream cylinder.