Mutual interference on transition of wake of circular cylinder

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An experimental investigation was carried out in the very near wake of a circular cylinder over the Reynolds number range of 260<Re<1.8×103. The aspect ratio of the cylinder was 4. The present study concerns the regular shedding mode of the wake, in which the large-scale primary vortex sheet and the small-scale individual and pairing secondary vortices are present. Based on a new conditionally sampling technique, there is mutual interference between the high-energy small-scale secondary vortices and the development of large-scale primary vortex sheet and of the strain field of primary vortex sheet on individual secondary vortices. The pairing vortices, however, do not significantly affect the large-scale vortices. In the transition regimes within this low Reynolds number range, in which transition of two-dimensional large-scale primary vortices to three dimensionality occurs, the disturbances of the individual and pairing secondary vortices excite the separated shear layer at the most amplified mode. Coupled with mutual interference, they play an important role in the transition. Correlation with the available and additional results in the upper transition regime and in the supercritical and transcritical regimes suggests the same mechanism of transition. The mutual interference of different types of vortices in the very near wake is the key factor for transition.