Flows around two nonparallel tandem circular cylinders

The paper presents a systematic experimental study on the dynamics of flow around two nonparallel tandem cylinders at a Reynolds number of 5.6 x 10(4). Three generic configurations of the cylinders are considered: 1 the upstream cylinder yawed and downstream cylinder upright, 2 both cylinders yawed oppositely, and 3 the upstream cylinder upright and the downstream cylinder yawed. Extensive measurements are conducted of the surface flow pattern, fluid forces, shedding frequencies, and velocity fields around the cylinders. The flow is classified into three regimes based on the behaviors of shear layers around the cylinders for all configurations. The wake in each regime is characterized in detail, including its recirculation strength, vortex formation length, wake width, Strouhal numbers, and mean and fluctuating fluid forces on the cylinders. Conceptual flow structure models are proposed for each configuration. It has been found that the flow around two nonparallel cylinders is characterized by spiral vortices, with either upward or downward motion or both. These vortices play a crucial role in fluid dynamics, producing a profound impact on the fluid forces as well as flow three-dimensionality.