Numerical study on flow past a confined half cylinder in two bluff arrangements

Two-dimensional flow past a half cylinder in the two bluff arrangements confined by parallel walls is studied for the range of Reynolds number as 1 <= Re <= 160 at a blockage ratio of beta = 0.2. A direct comparison is made of all results obtained for the two half-cylinder arrangements and the full cylinder. Critical Reynolds numbers signifying the onset of flow separation (Re-c1) and vortex shedding (Re-c2) have been identified for both bluff arrangements, the values of which are lower than that for the full cylinder of the same blockage ratio. The value of Re-c2 reported in the literature [Kumar et al 2016 Int. J. Heat Mass Transfer 102 417-425] for a confined half cylinder at beta = 0.25 has also been evaluated and clarified. The mean value of the coefficient of drag CD increases with Re in the vortex shedding regime for the half cylinder, which is well-known to manifest opposite trends with Re from the full cylinder. A possible explanation for this difference is provided. In addition, the pressure and friction (viscous) components are analyzed for all instances studied in both the steady and vortex shedding regimes, and provide an understanding of the competition between the forces due to pressure and friction acting on the cylinder with increasing Reynolds number. In particular, a very high percentage contribution (nearly 99%) of pressure drag to total drag is found at Re = 160 for the half cylinder with its flat surface facing upstream. Finally, flow features are detailed to further illustrate the fluid-structure interaction for the half cylinder.