EFFECTS OF ROUNDING ON FLOW CHARACTERISTICS PAST AN ANGULATED CYLINDRICAL OBJECT

초록

In the present numerical study, we aim at elucidating the effects of rounding on flow topology past an angulated cylindrical object. Change in flow topology significantly affects flow-induced forces on the object. We consider the rounded cylinders ranging from a square cylinder of height D to a circular cylinder of diameter D by rounding the four corners of a square cylinder with a quarter circle of fixed radius (r). An immersed boundary method was adopted for implementation of the cylinder cross-sections in a Cartesian grid system. The key parameters are Reynolds number (Re) and corner radius of curvature (r). A small rounding delays the flow separation towards the trailing rounded edges, resulting in lower lift fluctuation. The minimum mean drag also occurs when the sharp edges of a square cylinder are “partially” rounded. The optimal edge-radius ratio (r/d) for lift fluctuation or for mean drag depends upon Re, and high-Re flow tends to be more sensitive to small rounding. The main topological changes resulting from four-edge rounding can be obtained by leading-edge rounding alone. Trailing-edge rounding, however, plays a positive role in stabilizing the flow when the two types of rounding are combined.