Cylinders with Square Cross Section: Paths to Turbulence with Various Angles of Incidence

The path to turbulence in the wake of cylinders with square crosssection is investigated by means of direct numerical simulation, employing a two-dimensional spectral element method and Floquet linear stability analysis. The critical Reynolds number for the onset of the three-dimensional instability modes A, B, C and QP are reported for cylinder incidence angles between 0° and 45°. The Strouhal—Reynolds number relationship, and lift and drag coefficients are also investigated for these incidence angles. Reynolds numbers (based on the side length of the square) up to Re=300 are considered, and a significant variation in bifurcation scenarios are observed for the various incidence angles. At Reynolds numbers greater than Re ≈ 225 for an incidence angle of 45°, a previously unreported asymmetry is detected in the von Kármán vortex street. The cause of this asymmetry is investigated as it presents a possible alternative path to turbulence to that reported in the wakes of other bluff bodies.