Flow-induced forces and vortex transportation characteristics of three circular cylinders at subcritical Reynolds number

Abstract

Three-dimensional numerical simulation for the three circular cylinders at Re = 3900 is carried out by using the large eddy simulation (LES) in this paper. The present numerical model and parameters are verified by solving single cylinder and two cylinders cases. Then, the parameters consisted of spacing ratio (L/D) and incidence angle (α) are checked in three circular cylinders array. The fluid force and near-wake behavior of the two- and three-cylinder systems are analyzed with emphasis. Under a tight arrangement, there are three flow patterns: reattachment flow pattern, large-incidence-angle flow pattern, and biased flow pattern, corresponding to cases with incidence angles of 0, 45, and 90 degrees, respectively. The Strouhal number (St) of the three cylinders is essentially overlapping at α= 0° and α= 90°, the distinctive secondary peaks can be observed at the small spacing ratio in power spectral density (PSD). The mean pressure coefficient of midstream cylinder (MC) influenced by the number of cylinders is negative in the tandem arrangement at the stagnation point, accompanied by reattachment phenomenon the upstream surface of MC with L/D= 1.5. Placing the third cylinder between the two cylinders in a tandem arrangement significantly suppresses their lift oscillations. The phase difference (φum) between the fluctuating lift of the upstream two cylinders is highly sensitive to the incidence angle of the system.