Time-averaged and time-dependent computations of isothermal flowfields in a centerbody combustor

A numerical investigation of the near-wake region in a ducted bluff-body combustor by finite-difference computations is reported. The numerical predictions are based upon: (1) the Reynolds-averaged Navier Stokes equations and the k-epsilon turbulence model; and (2) the time-dependent, compressible Navier-Stokes equations, The standard K-epsilon turbulence model was modified to account for the effect of streamline curvature and for the preferential influence of normal stresses. The time-averaged calculations addressed the turbulent mixing under isothermal conditions in: (1) the large and small-scale centerbody combustor configurations, due to annular air flow and central CO2 flow; and (2) the two-dimensional mixing-layer configuration, due to two streams of nitrogen at different velocities. The time-dependent calculations addressed the near-wake flowfield of the large-scale centerbody combustor configuration with only the annular air stream present. The Reynolds-averaged predictions examined the influence of the turbulence model corrections and geometric scale under varying annular and central flows on: (1) the axial and radial distributions of the mean and fluctuating components of the axial and radial velocities and of the mean CO2 concentrations; and (2) the axial and the radial locations of the vortex center, as well as the magnitude and location of the minimum centerline mean axial velocity. Comparison of the predicted results with experimental data emphasizes and clarifies the complex flowfield interactions of the recirculating near-wake region.