The effect of angular misalignment on low-frequency axisymmetric wake instability

Abstract

The effect of angular misalignment on the low-frequency dynamics of the near wake of a blunt-based axisymmetric body is investigated at a Reynolds number of $Re=67\,000$. While for axisymmetric boundary conditions all azimuthal orientations of the wake are explored with equal probability, resulting in a statistical axisymmetry, an angular offset as small as $0.2^{\circ }$ is found to suppress the low-frequency large-scale behaviour that is associated with the erratic meandering of the region of reversed flow. As a result of the misalignment, the centroid of this backflow region is displaced from the model axis and remains confined around an average off-centre position. Spectral and modal analysis provides evidence that the erratic backflow behaviour occurs within a narrow angular range of deviations from axisymmetric conditions.