Dynamics of Compressible Vortex Rings and Circular Jets

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ABSTRACT Proposal Number: CTS-9622302 Principal Investigator: Virk/Hussain This is a project to carry out numerical simulations of circular turbulent jets in both the incompressible and compressible flow regimes. The aim is to study vortical structures first in incompressible jets and then extend this to the study of the role of compressibility in flow development. Vortex rings are the canonical coherent structures in turbulent jets. Their transition and interactions are the primary cause of entrainment and mixing in turbulent jets. The issues of interest in this study are the vorticity topology during non-linear evolution and transition, and the post transition structure. The complex helical wave decomposition will be used to reveal the separation of vorticity packets that lead to transition. A numerical data base will be developed that will allow the study of transition mechanisms, controllability using inflow perturbations, the dynamics of far field coherent structures and shock vortex interactions. A finite-volume code will be developed to initiate systematic studies of spatially evolving 3D jets. Low Mach number simulations of a single frequency perturbation will be used to determine the vortex dynamics responsible for the experimentally observed periodic/chaotic transitional flow regimes. The results of this effort will be used to improve low-dimensional dynamic models that will enable flow control. Axisymmetric simulations of supersonic jets will be used to determine the effects of shock-cell structure on coherent structure roll-up and interactions. This will be extended to the study of fully 3D, spatially evolving, supersonic jets in terms of vortex dynamics to understand the effects of shocks on coherent structure dynamics and their transition, as well as the evolutionary dynamics of the far field coherent structures. Compressible turbulent flows are technologically important. This study will provide insight that will lead to computational models that will be c apable of taking into account the effect of compressibility on flow instability and will lay the foundations for the development of flow control methods.