Kurzbeschreibung:
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
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