Observation of preferred instability modes in a mechanically excited thermal plume using Schlieren visualizations

An experimental study of the instability modes of a laminar axisymmetric thermal plume under symmetrical controlled disturbances of varicose type was carried out. The Schlieren technique was used to investigate the considered flow. The range of excitation frequencies over which the studied plume became unstable was determined. The size of the corresponding induced large-scale structures was analyzed in function of the disturbance frequency. The results obtained throughout this work confirmed the ability of a plume to behave like a frequencies filter.