Confinement Effects on Air Cross-Flow Over an Elliptical Cylinder

Cylinders in cross-flow encountered in engineering applications and in nature may or may not have confinement influence due to the presence and proximity of neighboring structures. On the other hand, fluid-structure experiments conducted in wind and water tunnels are typically restricted and affected by confinement. The confinement is usually expressed in terms of the blockage ratio, which is the cylinder/tunnel cross sectional area ratio. Therefore, a good understanding of the role of blockage is critical in further advancing the knowledge of fluid-structure interactions. The effect of blockage ratio on the fluid flow over a circular cylinder has been addressed by some authors, but, literature on elliptical cylinders is limited. In this study, fluid flow over an elliptical cylinder with axis ratios (minor to major axis ratio) of 1 (circular cylinder), 0.5 and 0.4 were investigated numerically, using control volume approach in FLUENT, at a Reynolds number (based on the hydraulic diameter) of 40. The flow was considered to be uniform at the entrance (40d and 15d upstream from the center of the cylinder for unbounded and bounded flow respectively) of the two dimensional computational domain, steady and parallel to the major axis of the cylinder. Blockage ratios of 0 (un-confined scenario), 0.07 and 0.12 were studied because of the availability of experimental data at these blockage ratios for the circular cylinder case. From the simulation output, the velocity distributions were analyzed in detail. The increase of blockage ratio increases the drag coefficient and reduces the wake size of the circular cylinder. On the other hand, the increase in blockage ratio increases the wake length of elliptical cylinders with (minor/major) axis ratios of 0.5 and 0.4. These results agree well with the available data in the literature.