Numerical Simulations of the 3D Unsteady Flow in a Bluff-Body Combustor

Abstract

In this work, results from numerical investigations of a bluff body stabilized flame are reported. Here, the fuel is injected a short distance upstream of the bluff body within the combustor, as is the case in practical ramjets and afterburners. In this situation, both the mixing of the fuel and air as well as the subsequent combustion stabilized at the bluff body are altered by the acoustic field excited by unsteady heat release in the combustion zone. The present study focuses on the unsteady flow in this geometry for different combustor configurations. These configurations correspond to different axial locations of the bluff body and different combustor lengths. Numerical simulations of the non-reacting as well as reacting flow in the bluff body combustor have been carried out for selected configurations using FLUENT. Both realizable k - ε and SST k - ω model have been used for modelling turbulence. Chemistry is modelled using a laminar 3 step model. Second order accurate spatial as well as temporal discretization has been used. DFT of the pressure-time data have been performed to extract the dominant frequencies of the oscillations. Numerically predicted frequencies are compared with experimental values (reported in a companion paper) and the predictions are seen to agree reasonably well with the experimental data. It is also shown that the present calculations are able to predict both the duct acoustic modes as well as the vortex shedding mode.