Numerical Study of the Instability and Flow Transition in a Vortex-Ring/Wall Interaction

Abstract

Instability and fl w transition of a vortex ring impinging on a wall were investigated by means of large-eddy simulation for two vortex core thicknesses corresponding to thin and thick vortex rings. Various fundamental mechanisms dictating the fl w behaviours, such as evolution of vortical structures, instability and breakdown of vortex rings, development of modal energies, and transition from laminar to turbulent state, have been studied systematically. Analysis of the enstrophy of wrapping vortices and turbulent kinetic energy (TKE) in fl w fiel indicates that the formation and evolution of wrapping vortices are closely associated with the fl w transition to turbulent state. It is found that the temporal development of wrapping vortices and the growth rate of axial fl w generated around the circumference of the core region for the thin ring are faster than those for the thick ring. The azimuthal instabilities of primary and secondary vortex rings are analysed and the development of modal energies reveals the fl w transition to turbulent state. The law of energy decay follows a characteristic k −5/3 law, indicating that the vortical fl w has become turbulent. The results obtained in this study provide physical insight into the understandingof the instability mechanisms relevant to the vortical fl w evolution.

Flow characteristics and formation optimization of vortex ring air supply

“…Structured grid used in this study. The accuracy of different turbulence models was verified, including the Laminar model, 31 RSM model, and LES model 32–36 . The corresponding $$$ {y}^{+} $$$ values were selected for different turbulence models.…”

“…The accuracy of different turbulence models was verified, including the Laminar model, 31 RSM model, and LES model. [32][33][34][35][36] The corresponding y + values were selected for different turbulence models. For the RSM model, the high Reynolds number turbulence model requires higher y + value (30 < y + <500).…”