Characteristics of the flow around four cylinders of various shapes

Abstract

Characteristics of flow around four cylinders of various shapes in the square configuration were numerically investigated using a vortex-in-cell method. The flow patterns drastically depend on the cylinder geometry, such as equilateral triangle, square, regular hexagon, and circle. In the cases of left, right, and up/down triangles, the vortices are synchronously shed from the cylinders. The fluctuations of drag (Cd) and lift (Cl) coefficients exerted on these cylinders are also synchronous. The magnitudes of these fluctuations of left triangles are small, while those of right and up/down triangles are greater. In the cases of circles and squares rotated 45 degrees, the vortices shed from the cylinders are nearly synchronous, and the fluctuations of Cd and Cl are of a higher magnitude. In the cases of down/up triangles, unrotated squares, and regular hexagons, the flow instability was investigated in a range of Reynolds numbers from 65 to 300, and the flow patterns are classified into Steady, notRolling-twoStreets, Rolling-twoStreets, notRolling-Merging, and Rolling-Merging. The fluctuations of Cd and Cl exerted on these cylinders are non-synchronous and of a strong magnitude. The lowest frequency of the vortex shedding was noticed in cases of down/up triangles and unrotated squares, in which the fatigue of the cylinder cluster is highly remarkable. The two most optimal geometries of the cylinder are circle and square rotated 45 degrees.