Influence of vibrational non-equilibrium on the dynamics of velocity gradients in turbulent flows*

In hypersonic turbulent flow fields, air molecules get vibrationally excited. Further, the flow residence time over a hypersonic vehicle may be too small such that the vibrational and the translational modes of internal energy may exist in a temporally evolving non-equilibrium state. This non-equilibrium leads to modified energetics in the flow field that in turn may affect various non-linear processes of turbulence. In this work, our objective is to identify, isolate and examine how the vibrational non-equilibrium phenomenon specifically influences the dynamics of velocity gradients.  We perform well-resolved direct numerical simulation (DNS) simulations of decaying isotropic turbulence, including the physics of vibrational non-equilibrium of air molecules. These simulations are performed for a set of initial conditions, wherein the vibrational Damkohler number and the initial ratio of vibrational to translation-rotational energy are used as simulation parameters. We plan to demonstrate how the vibrational non-equilibrium process specifically influences the solenoidal and dilatational aspects of the hypersonic velocity field. Further, we also discuss how the pressure Hessian tensor acts as an intermediary through which the vibrational non-equilibrium shapes the behavior of the velocity gradient field.