Identification of Flow Structures during Irregular Vortex Shedding

Surface pressure on a square cylinder mounted near a wall and velocity measurements in the wake are analyzed for a flow at a Reynolds number of 20000. Regular and intermittent vortex shedding regimes are consifered using classical spectral and continuous wavelet transform analysis. For large cylinder-to-wall spacing vortex shedding is regular and there is evidence of secondary large scale structures in addition to the shed vortices. In the intermittent regime, the secondary structures contain significantly less energy. During the interruption of shedding, large-scale, high energy structures can be identified