Numerical Study of Stratified Flames Using Reynolds Averaged Navier Stokes Modeling

Area of Science:

• Combustion science
• Computational fluid dynamics
• Turbulence modeling

Background:

• Stratified flames present complex combustion dynamics.
• Accurate numerical modeling is crucial for understanding flame behavior.
• Previous studies often relied on computationally intensive methods.

Purpose of the Study:

• To develop and validate a computationally efficient numerical model for stratified flames.
• To investigate the impact of varying stratification ratios on flame characteristics.
• To analyze the effects on temperature, combustion efficiency, and flame location.

Main Methods:

• Reynolds averaged Navier-Stokes (RANS) technique for numerical modeling.
• Validation against experimental data from the Cambridge dual annulus swirl burner.
• Utilized the RNG k-ε turbulence model and SG-35 skeletal chemical mechanism.
• Achieved a 99.75% reduction in computational time compared to LES.

Main Results:

• The model accurately predicted scalar and vector quantities.
• Intense burning near the bluff body observed at stratification ratios (SRs) of 1 and 2.
• Flame region shifted downstream for SR > 2 due to rich inner annulus mixtures.
• Maximum temperature increased by 24.1% from SR=1 to SR=2.
• Combustion efficiency improved by 267% at SR=2.

Conclusions:

• The RANS model with RNG k-ε and SG-35 provides an efficient and accurate tool for stratified flame simulation.
• Mild stratification (SR=2) optimizes temperature and combustion efficiency.
• Flame behavior is highly sensitive to the equivalence ratio and mixing dynamics in stratified flames.