Enstrophy Transport During Longitudinal Combustion Instability in a High-Pressure Rocket Combustor

Enstrophy transport involves both large- and small-scale turbulence dynamics. Therefore, understanding the various physical phenomena contributing to its production and destruction is critical. This understanding is essential for comprehending flame-turbulence interactions. This study utilizes a highly resolved adaptive mesh refinement (AMR) based large-eddy simulation (LES) dataset to examine enstrophy transport in a high-pressure rocket combustor experiencing longitudinal combustion instability. Specifically, the four terms of the enstrophy transport equation—vortex stretching, dilatation, baroclinic torque, and viscous dissipation are analyzed both in physical and state-space. Results indicate that vortex stretching and baroclinic torque predominantly produce enstrophy in fuel-rich regions, while dilatation and viscous dissipation contribute to its destruction. Notably, baroclinic torque, arising from the non-alignment of density and pressure gradients, exhibits the highest enstrophy production. This study also reveals a quasi-cyclic behavior of enstrophy dynamics, with production phases interspersed with dissipation phases, correlating with flame weakening and re-intensification. These nonlinear enstrophy fluctuations impact mixing and unsteady heat release, amplifying acoustic waves and sustaining combustion instabilities.