Flow uniformity characterization in catalytic converters under turbulent inlet conditions
Typ
Projektarbete, avancerad nivå
Program
Publicerad
2022
Författare
Tylén, Oskar
Larsson, Jacob
Murali, Aravind
Rangaswamy, Sunil
Peyvandi, Ehsan
Larsson, Axel
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
In the sectors utilizing the combustion of fossil fuels, catalytic converters are commonly
employed to reduce dangerous gases generated by combustion engines. For greater efficiency,
it is critical to understand the exhaust flow homogeneity inside the converter.
This work attempts to evaluate the added value of using Detached Eddy Simulation (DES)
simulation over Reynolds-Averaged Navier-Stokes (RANS) simulation for analysis of turbulent
flow inside catalytic converters. The meshing and simulation of the domain was
carried out using ANSYS FLUENT and ANSYS Workbench. Initially a RANS simulation
with k-ω SST turbulence model was carried out for a specific case to understand the
behavior of the time averaged flow field with modeled turbulence and its effect on uniformity
index. The results from the RANS simulation were, together with definitions of
turbulent length scales, used to develop a mesh for DES simulation. In this process it was
found that in order to resolve a sufficient amount of turbulence upstream of the monolith
inlet, the DES simulation required a considerably finer grid than the RANS simulation.
The DES simulation with k-ω SST model was used to simulate multiple retention times,
attempting to achieve a quasi steady flow with resolved velocity fluctuations. However
due to constraints on computational power, simulating until statistical convergence was
not possible. The time averaged quantities were extracted from the DES simulation in
order to make a fair comparison with RANS results. The uniformity indices of RANS
and DES were then compared throughout the monolith of the catalytic converter. A
difference of ∼1-1.5% in uniformity index was found from this comparison. Further more
it was found that the resolved turbulence in the DES generates fluctuations of ∼3-6% in
the uniformity index based on instantaneous quantities.
The work concludes that for the exact case simulated, the possibility of increased accuracy
when predicting uniformity index with DES instead of RANS does not outweigh the
increased computational cost. However for different flow conditions, with larger mean
velocity magnitude and less uniform flow, the measured difference between RANS and
DES could make a larger difference for prediction of catalytic conversion efficiency. Hence
in these cases it is possible that DES simulations are worth their computational cost.
Whether this is the case or not would have to be examined through further research
before coming to any definitive conclusions.
Beskrivning
Ämne/nyckelord
Catalytic converters , Flow uniformity , Detached-eddy simulation , Reynolds averaged navier stokes simulations