The Zimont TFC Model Applied to Premixed Bluff Body Stabilized Combustion Using Four Different RANS Turbulence Models

Abstract

The Volvo Aero Corp. (VAC) Triangular Bluff Body Stabilized Combustion rig VR-1 has been extensively researched both in terms of experiments and theoretical treatment. Previous CFD work has concentrated on Reynolds Averaged Navier-Stokes (RANS) models combined with the Level Set Flamelet Library approach. Large Eddy Simulation (LES) has also been applied to the case. In this paper the Zimont Turbulent Flame Closure (TFC) model has been investigated in conjunction with the k-ε, k-ω, SST k-ω and RSM RANS model implementations in ANSYS CFX 10.0. It is shown that the various RANS models generate significantly different results in terms of turbulent velocity and integral length scale fields. These parameters influence the computed turbulent flame speed. The turbulent viscosity fields also differ substantially between the various RANS models. This will affect the computed degree of flame front diffusion. For the investigated case; the TFC model combined with the k-ω model fairly accurately captures the recirculation zone length and overall turbulent flame speed. The measured case however displays Kelvin-Helmholtz induced oscillations of the shear layers behind the bluff body. This will combine with the free-stream turbulence and turbulence generated along the upstream surfaces of the bluff body to distort the flame sheets. The two flame fronts will also be subjected to other (unquantified) combustion related instabilities. The combined effect is not captured well in steady state RANS. The analysis is therefore seen to grossly under-predict flame front diffusion, regardless of turbulence model.