mr. nektarios koutsourakis1,2 dr. alexander venetsanos2
DESCRIPTION
ADREA-HF CFD CODE Constantly developing Latest additions: LES (Large Eddy Simulation) Parallel solver Arbitrary number of species Combustion Back tracking GUI pre and post processor (called EDes) Advantages: Robust, powerful and general Specialization in environmental applications ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODETRANSCRIPT
[ID 204] Evaluation of ADREA-HF LES against Hydrogen release
dispersion
Mr. Nektarios Koutsourakis1,2 Dr. Alexander Venetsanos2 Prof. John
G. Bartzis1 4th International Conference on Hydrogen Safety San
Francisco, California, September 12-14, 2011 1 University of West
MacedoniaGreece 2 NCSR DemokritosGreece ICHS 2011, #204 LES
MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A
NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE
ADREA-HF CFD CODE Constantly developing
Latest additions: LES(Large Eddy Simulation) Parallel solver
Arbitrary number of species Combustion Back tracking GUI pre and
post processor (called EDes) Advantages: Robust, powerful and
general Specialization in environmental applications ICHS 2011,
#204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A
NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE
ADREA-HF CFD CODE ADREA specializes in dispersion
applications
ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION
WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF
CFD CODE ADREA-HF CFD CODE GUI environment for pre and post
processing
ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION
WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF
CFD CODE LARGE EDDY SIMULATION Between DNS and RANS
Navier-Stokes math. analysis: impossibly difficult
DNS:Fully-resolved NS Cost Re2.75(for wall-bounded flows Re3.5)
RANS:Time-averaged NS Fast, widely tested, usually accurate enough
LES:Spatially-filtered NS Cost near wall: Re2.4 ! (at outer layer
Re0.5) Converges to DNS. As in DNS, LES needs: a) averagingb)
demanding boundary conditions Suggested were RANS fails: transient,
separated flow DNS: Thousands of years to simulate 1s of flight
RANS: Good for steady state problems, with no big separations ICHS
2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION
WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF
CFD CODE ENERGY CASCADE LES solves most of the turbulence
ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION
WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF
CFD CODE LES EQUATIONS AT ADREA-HF Compressible volume-filtered
Navier-Stokes
ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION
WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF
CFD CODE LES EQUATIONS AT ADREA-HF Alternative subgrid model:
RNG-LES
ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION
WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF
CFD CODE LES AT ADREA-HF Numerics
ADREA/SIMPLER algorithm Solver: Parallel BiCGstab with parallel
Schwarz preconditioner. Speedup with 2 CPUs up to 1.7 Numerics:
Deferred correction central scheme for convection Crank-Nicolson 2d
order for time advancement Linear upwind with VanLeer limiter for
concentration For more: Venetsanos, A. G., E. Papanikolaou and J.
G. Bartzis, 2010: The ADREA-HF CFD code for consequence assessment
of hydrogen applications. Int. J. Hydrogen Energy, 35, 3908. ICHS
2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION
WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF
CFD CODE TEST CASE HySafe INERIS-6C experiment
1g/s H2 for 240s Jet 20mm Room 3.78 * 7.2 * 2.88m Jet exit velocity
38m/s ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND
ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING
THE ADREA-HF CFD CODE TEST CASE SETUP Simulation details
Standard Smagorinsky with Cs=0.1 Total number of cells in the room:
CFLmax=0.3 Minimum mesh resolution: 0.02*0.02*0.053 m Simulation
time in a workstation: 15 days for the release phase (240s);dtav1=
s + 2 days for the first 260s of the post-release phase ICHS 2011,
#204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A
NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE
TEST CASE SETUP Geometry, sensors, part of the grid
ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION
WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF
CFD CODE RESULTS Comparison with experiment
Photo from experiment ADREA LES An asymmetry on the ceiling can be
noticed (higher C towards the sensors side of the room). The plume
at the higher parts of the jet seems to be slightly wider in the
simulation. ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND
ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING
THE ADREA-HF CFD CODE RESULTS Video of the Hydrogen
propagation
ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION
WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF
CFD CODE RESULTS Concentration contours animation
A flow field develops that transfers the hydrogen along the ceiling
and then downwards along the side walls, which have higher
concentrations than the neighbouring regions of the same height.
Thus the plume takes a mushroom shape. ICHS 2011, #204 LES
MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A
NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE
RESULTS Comparison with sensors
Each plot should be explained, along hydrogen route: Starting from
16 to 1 to 7 to 12. Why the slope increases along route, why the
difference of release and diffusion decreases, etc. ICHS 2011, #204
LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A
NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE
DISCUSSION Some remarks
In general very good agreement High turbulence during release
phase, only Release overestimated, especially near source. Very
difficult for CFD and for turbulence modelling to capture the
physical processes next to the source Diffusion underestimated
(possible experimental asymmetry?) - improvement with better grid
Better agreement is prevented from experimental inaccuracies and
numerical discrepancies I think release is overestimated due to
inadequacy of CFD to see what exactly happens at the emission area.
That is a very difficult point that needs very advanced models ICHS
2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION
WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF
CFD CODE FURTHER EXAMINATION Cs value influence (release phase
-coarse grid)
Jet axis sensors Ceiling sensors Side wall sensors Sensor 16 Sensor
14 Sensor 13 Sensor 1 Sensor 4 Sensor 6 Sensor 7 Sensor 8 Sensor 9
Sensor 10 Sensor 12 Only 80s-160s measurements taken into account!
Max diffusion close to 0.12 ICHS 2011, #204 LES MODELLING OF
HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT
PRESSURE GARAGE USING THE ADREA-HF CFD CODE DISCUSSION Cs affects
the results
Cs (SGS modelling in general) important near jet At the ceiling, no
Cs influence (buoyancy dominates) Non-monotonic behaviour
(increasing the Cs gives better results, but up to a limit) Worst
Cs by far: 0.2 ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE
AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE
USING THE ADREA-HF CFD CODE FURTHER EXAMINATION C variances for
each Cs
C variance = mean (Ci2) VARIANCE IS A MEASURE OF RESOLVED
TURBULENCE if total turbulence is higher (while variance being
same), it means that the SGS (unresolved) is higher. To calculate
the variance I only used values from 74s till 166s for all cases.
ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION
WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF
CFD CODE DISCUSSION A critical balance: resolved vs. SGS
turbulence
As we go away from the jet, variance (and resolved turbulence
intensity) drops Two mechanisms compete: - Modelled SGS turbulence
- Resolved turbulence (generally low if SGS is high) With Cs=0.2,
very high artificial viscosity causes more laminar flow and lower
fluctuations Resolved turbulence is higher with Cs=0.1, but total
turbulence seems to be higher with Cs=0.12 ICHS 2011, #204 LES
MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A
NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE
FURTHER EXAMINATION Evaluation of RNG-LES (run not finished
yet)
ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION
WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF
CFD CODE DISCUSSION RNG LES seems to be an improvement
RNG LES provides in general better results Improvement towards the
right side for sensors both close to the jet (turbulent flow) and
far from it (laminar flow). That was not the case by varying Cs
Resolved turbulence seems to decrease close to the jet and increase
far from it RNG LES is believed to better model the subgrid scales
for both the turbulent and the laminar flow Suggestible when the
turbulence intensity varies ICHS 2011, #204 LES MODELLING OF
HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT
PRESSURE GARAGE USING THE ADREA-HF CFD CODE CONCLUSIONS I
Acceptable results and physical insight
LES results are good, given all numerical and experimental
inaccuracies Overestimation during release phase (close to jet)
Underestimation during diffusion phase (and far from jet) Attempt
to investigate the balance between resolved and SGS turbulence with
parametric analysis of Cs RNG LES seems to behave slightly better
in both turbulent and laminar parts of the flow ICHS 2011, #204 LES
MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A
NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE
CONCLUSIONS II LES is good, but not for everyday use
ADREA-HF has now tested LES in hydrogen release LES can provide
peak concentrations (good for flammable mixtures or for calculation
of dosages) LES can provide concentration statistics LES many times
more expensive than RANS LES is not RANS++ There is not good LES
there is good CFD In general, in any good CFD code LES can be added
ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION
WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF
CFD CODE THANK YOU Acknowledgements: Greek Scholarships Foundation,
Municipality of Aghia Varvara ICHS 2011, #204 LES MODELLING OF
HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT
PRESSURE GARAGE USING THE ADREA-HF CFD CODE