Tracking Virtual Flame Particles for Studying Flame Dynamics

Objective of this theoretical thesis work is to gain an in-depth understanding of the flame dynamics during turbulent combustion processes, which is of great importance for the stable, efficient and clean burning of fuels. The topic covers mainly the effect of the interaction between the turbulent flow and combustion reaction. The flame is stretched due to the unsteady, non-uniform flow in terms of curvature and straining, which locally leads to a modified balance between underlying transport and reaction processes. In extreme case, the flame may be extinguished by a high stretch rate on the flame surface. As this interaction process occurs at a wide range of length and time scales, most existing models take simply the unstretched, laminar flame speed for the interpretation of local flame characteristics, e.g. in Flamelet models. This assumption is not valid especially under conditions of highly turbulent and unsteady flows.

Previous studies on flame dynamics are mostly limited to global flame features, such as time mean total flame surface or flame angle, which neglects the effect of time history of the turbulent flow. A novel method based on tracking virtual massless particles along the flame surface will be used in this thesis work for a detailed analysis of the correlation of modified transport processes by turbulent flow stretch. Direct numerical simulation on simple 2D oscillating jet flames will be carried out using the OpenFOAM code at varying fluctuating time scales. The behaviors of local and global flame speed in response to unsteadiness of the incoming flow will be analyzed and at best, recast to a correlation law by means of the flame’s relaxation time. The computational grids as well as tools required for DNS and particle tracking are already developed.

Detailed work steps include:

1. Literature research and familiarization with required tools 

2. Running DNS for different inflow conditions

3. Detailed analyses of the simulation results 

4. Summary and presentation of the work