LAUSR

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 ( C d ) and lift ( C l ) 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 C d and C l 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 C d and C l 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.