Transient numerical simulations of a cold-flow bidirectional vortex chamber

Abstract

Bidirectional chambers are well-studied in terms of the flow structure and influence of their input parameters. However, most of the available studies are based on steady-state or time-averaged research methods and do not allow to obtain data on bidirectional flow dynamics over time. The present paper reports on detailed numerical studies based on detached eddy simulations (DESs) and unsteady Reynolds-averaged Navier–Stokes methods applied for two vortex chambers with different aspect ratios. A comparison of the numerical results with the available experimental data shows that the DES method gives the most accurate results on bidirectional flow structure, turbulent fluctuations, and precessing vortex core (PVC) motion. A notable feature of the studied bidirectional flow is the central recirculation zone (CRZ) formation, which is correctly predicted by the DES method only. The presence of a CRZ in a bidirectional flow has a significant effect on turbulent velocity fluctuations and PVC behavior. It is found that CRZ formation leads to a significant decrease in radial and circumferential velocity fluctuations whereas the axial velocity fluctuations are slightly increased. Additionally, the paper reports new findings on CRZ and PVC interaction in bidirectional flows. PVC motion is almost completely nullified by the presence of a CRZ. This can prove useful in many industrial applications of bidirectional chambers, e.g., vortex thrusters and gas turbine combustors. The bidirectional swirling flow transient properties studied in this paper could assist in determining the most efficient operational modes and geometric configuration of industrial chambers as well as enabling control of turbulent fluctuations, which would allow for reliable ignition and stable combustion.