Spectral Analysis of Flow around Single and Two Crossing Circular Cylinders Arranged at 60 and 90 Degrees

Abstract

Two modal decomposition techniques, including proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD), were used to identify the wake patterns past single and two crossing cylinders in 60° and 90° arrangements with gap ratio G = 4. The flow was simulated using direct numerical simulations (DNS) for Reynolds numbers Re = 100. From modal analysis, the flow’s spatial scale decreased with increasing modal frequency. Two main modes were identified in the wake of the cylinders, namely spatially antisymmetric and symmetric modes. Antisymmetric and symmetric modes were related to the cylinders’ vortex shedding and shedding vortices’ shift motion, respectively, whose frequencies were odd and even multiples of the cylinders’ lift force frequency. In addition, a low-frequency mode concerning the shadowing effect of the downstream cylinder (DC) in 90° arrangement was found in the wake of the DC centre.

Keywords

• low-dimensional models
• vortex dynamics
• wakes