On sustaining turbulence production in interacting supersonic streamwise vortices

Interacting supersonic streamwise vortices have been investigated as a means to enhance mixing at supersonic velocities. However, the turbulence dynamics associated with this class of flow has been left largely unexplored despite turbulence playing a major role in the achievement of molecular mixing. For this reason, the process of turbulent kinetic energy production in interacting supersonic streamwise vortices is investigated in this work. Specifically, the link between the mean flow motion and turbulence, represented by the production term of the turbulent transport equation, is analyzed. An approach is proposed in which the mean flow strain rates can be cast such that their intensity and morphology properly couple with the requirements imposed by the Reynolds stresses that, in the framework of this work, are shown to be intimately linked with the resulting plume morphology. The analysis is leveraged for the design of a mode of vortex interaction targeted to maintain a positive production of turbulent kinetic energy in the downstream evolution. The resulting configuration was experimentally investigated in a Mach 2.5 flow by stereoscopic particle image velocimetry. The results from these experiments show that the turbulence production remained positive and sustained turbulence levels, a unique result in the available literature. The role of turbulence anisotropy and the principal direction of negative planar strain rates are highlighted in detail in this work.