Vortex shedding and heat transfer in rotationally oscillating cylinders

Wake formation and heat transfer from a rotationally oscillating circular cylinder in cross-flow at $\mathit{Re}= 750$ are studied. Two aspects, the effect of cylinder forcing on vortex shedding and the effect of the wake structures on convective heat transfer, are studied. Cylinder forcing conditions range between $0.09 \leq \theta _{PP} \leq 2.09$ , where $\theta _{PP}$ is the peak-to-peak oscillation amplitude in radians and $0.70 \leq F_{R} \leq 3.16$ , where $F_{R}$ is the ratio of forcing frequency to natural shedding frequency. Digital particle image velocimetry (DPIV) is used to obtain quantitative wake structure information. Wake modes, and regions of the parameter space in which they occur, are identified for both heated and unheated cylinders. For the heated cylinder, cylinder forcing is found to affect the convective heat-transfer rate. Certain wake modes, including newly discovered wake modes synchronized over multiple oscillation cycles, are found to correlate with significant heat-transfer enhancement. Cylinder tangential velocity is also found to affect the heat-transfer rate in certain regions of the parameter space.