Numerical Simulations of the Flowfield in a Central-Dump Ramjet Combustor. I. Tests of the Model and Effects of Forcing

摘要

This paper presents results of numerical simulations of the cold flow in a central dump ramjet combustor. Tests of the boundary conditions and numerical resolutions are used to perform the simulations. The simulations are used to isolate and study the interaction between acoustic waves and large scale vortex structures. A strong coupling between the acoustic modes of the chamber and large scale vortex structures is observed. The results in the early part of the calculations indicate unforced natural vortex growth near the entrance to the combustor (dump plane) at a frequency close to that of the first longitudinal acoustic mode. With time, the acoustic modes shift the frequency of the most amplified vortex rollup mode near the dump plane into resonance with the acoustic mode. The simulations indicate that the location in space where the modes grow can also be shifted by acoustic forcing. An interesting feature observed in the simulations is a low frequency mode corresponding to the arrival of the merged vortex structures at the choked exit. This mode causes major changes in the merging pattern of the vortices.