Heat transfer enhancement and vortex flow structure over a heated cylinderoscillating in the crossflow direction

Experiments are preformed to study the flow structure and heat transfer. ov er a heated oscillating cylinder. Both flow visualization using a smoke wir e and local hear transfer measurements around the cylinder were made. The e xcitation frequencies of the cylinder are selected at F-e/F-n = 0, 0.5, 1, 1.5, 2, 2.5 and 3. These include excitations at harmonic, subharmonic, supe rharmonic, and nonharmonic frequencies. Synchronization of vortex shedding with the cylinder excitation occurs not only at F-e/F-n = 1 but also at F-e /F-n = 3, which can greatly enhance the heat transfer. The simultaneous enh ancement of heat transfer at the stagnation point, its downstream region, a nd the wake region of the flow suggests that different modes of instabiliti es occurring in the shear layer of the near wake are actually initiated and amplified far upstream in the stagnation point, which were suppressed in t he accelerated flow region and re-amplified in the decelerated flow region. As long as the dominant mode of the instability is amplified by the excita tion of cylinder, enhancement of heat transfer can be obtained. During the experiments, the Reynolds numbers vary from 1600 to 4800, the ratios of osc illation amplitude to diameter of the cylinder from 0.064 to 0.016.