| This thesis presents an experimental study of organized structures in the turbulent near wakes of single, two and three side-by-side circular cylinders, covering four topics.; Firstly, the relationships between logitudinal (ribs) and spanwise vortical structures in the turbulent near wake of a circular cylinder were investigated. Three components of vorticity in the wake of a circular cylinder were measured simultaneously with a combination of four X-wire probes.; Secondly, interactions between spanwise vortical structures, momentum and heat transport in the turbulent wake of two side-by-side circular cylinders were studied. The results point to a significant effect of T/ d on the topology and transport characteristics. The streamwise evolution of the vortex street is also discussed in detail.; Thirdly, interaction between turbulent simple wakes is determined. Using the same three-wire probe mentioned above, velocity and temperature fluctuations were measured in the turbulent wakes generated by single, two and three side-by-side circular cylinders (one of them was heated slightly). The superposition hypothesis, as proposed by Bradshaw and his co-workers, is also examined for the present complex wakes.; Finally, the effects of unequal cylinder spacing on the vortex streets behind the three side-by-side cylinders were studied. Various techniques were used in this experimental study, including hot-wire technique, laser Doppler anemometry (LDA) and laser-illuminated flow visualization the equally and unequally spaced cylinders in terms of the pressure around the cylinders, drag, lift, dominant frequencies, vortex formation and downstream evolution. The flow topology (patterns) is also discussed in detail. (Abstract shortened by UMI.)... |
