Phenomenology of turbulence production in merging process of supersonic streamwise vortices
Journal of Propulsion and Power
Merging of corotating vortices is of primary interest in the field of supersonic mixing due to the ability of two or more structures to coalesce and form a larger one which enhances the stirring motion and straining in the flow, thus promoting turbulence production and mixing augmentation. During experimental efforts aimed at quantifying mean and fluctuating flowfields produced by the merging of two supersonic streamwise corotating vortices through stereoscopic particle image velocimetry, it was noticed that both the strain rates and turbulent kinetic energy would peak within the elongated merger’s vorticity patch. The article discusses how this is in fact a counterintuitive phenomenon and shows that a possible explanation can be given by studying the flow within a frame of reference which rotates with the merger itself. It will be shown how the merger is surrounded by a different flowfield than that measured in the laboratory frame of reference, characterized by the presence of recirculation zones referred to as ghost vortices. These vortices introduce large rates of strain within the merger, thus providing a possible justification for the high levels of turbulence attained within the rotating structure. The experimental findings are strongly corroborated by reduced-order, inviscid simulations, showing the formation of similar structures and clarifying the presence of peaks of strain rates within the merger.
Fabrizio Vergine, Davide Viganò, and Luca Maddalena. "Phenomenology of turbulence production in merging process of supersonic streamwise vortices" Journal of Propulsion and Power (2021): 231-241. https://doi.org/10.2514/1.B38002