Near wake of a circular cylinder submitted to blowing – II: Impact on the dynamics

The near wake of a porous circular cylinder in cross-flow submitted to blowing through its whole surface is experimentally studied. The blowing impact on the Strouhal number exhibits a linear decrease of the vortex shedding frequency with the blowing ratio. A simple model representing this decrease as a function of the injection rate is developed, based on the wake static pressure profile evolution. The main flow temperature influence is also investigated in case of non-isothermal blowing and is shown to have no effect on the Strouhal number evolution. Finally, the interaction between the blowing and the shear layer is investigated through a spectral analysis of the velocity signal. A modification of the shear layer power spectrum is observed when injection occurs. The dynamics are slowed down and characteristic patterns, denoted sub-peaks, appear while the relationship between the von Kármán and the shear layer frequencies without blowing remains valid.