Absolute Instability Analysis of the Vortical Structure in the Rectangular Plate Wake

Vortical structures in the wake of the axisymmetric bluff body were investigated using an absolute instability analysis. The wake of the rectangular plate has different frequency components for vortical structures in major and minor planes. On the condition that the flows in both planes are parallel individually, the absolute instability analysis revealed that the unstable frequency obtained showed a good agreement with the shedding frequency of the hairpin shape vortex in the minor plane. In the major plane. it was found that an other frequency component related to the meandering vortex structure was also associated with the unstable instability. In an analysis of the major plane. it was shown that there are two saddle points in the complex field which express the dispersion relation.