5th European Review Meeting on Severe Accident Research (ERMSAR-2012) Cologne (Germany), March 21-23, 2012
Final results of the SARNET Hydrogen deflagration Benchmark Effect of turbulence on flame acceleration
A. Bentaib1, A. Bleyer1, N. Chaumeix2, B. Schramm3, M. Höhne3, P. Kostka4, M. Movahed5,
T. Brähler6, H. Seok Kang7, K. Sang-Baik7, M. Povilaitis8
1) IRSN, France 2) CNRS, France 3) GRS, Germany 4) NUBIKI, Hungary
5) AREVA, Germany 6) RUB, Germany 7) KAERI, KOREA 8) LEI, Lithuania
Summary
In case of a severe accident in a light water nuclear reactor, hydrogen would be produced during reactor core degradation and released into the reactor building. This could subsequently raise the potential of a combustion hazard. A local ignition of the combustible mixture may generate standing flames or initially slow propagating flames. Depending on geometry, mixture composition and turbulence level, the flame can accelerate or be quenched after a certain distance. The loads generated by the combustion process (increase of the containment atmosphere pressure and temperature) may threaten the integrity of the containment building and of internal walls and equipments. Turbulent deflagration flames may generate high pressure pulse, temperature peaks, large pressure gradients and even shock waves, which could seriously damage specific containment components, internal walls and/or safety equipment. The evaluation of such loads needs codes, which should be used with a high level of confidence.
Actually, turbulence effect on flame acceleration, flame deceleration and flame quenching mechanisms has not been completely well understood and further model development and validation are needed. For this purpose, hydrogen deflagration benchmark exercise had been organized in frame work of SARNET II project. Three tests performed on ENACCEF facility had been considered. They concern vertical flame propagation in initial homogenous mixture with 13% hydrogen content and different geometrical configurations. Three blockage ratios of 0, 0.33 and 0.63 had been considered to generate different levels of turbulence. The lumped parameter (LP) code ASTEC and the CFD codes CFX, COM3D and FLACS were used.
This paper presents the results of blind and open phases of the ENACCEF benchmark. The first part describes experiments made in the ENACCEF test facility which is a vertical stainless steel setup, which totalizes a length of 4.9 m. It is constituted of two main parts: the acceleration tube (length 3.2 m, inner diameter 154 mm), and the dome (length 1.7 m, external diameter 750 mm).
In the second part of this paper, both blind and open simulation results of the experiments are described and discussed. Conclusions and recommendation of the next benchmark step are given in the end.
KEY WORDS : Hydrogen, Combustion, ENACCEF, CFX, ASTEC FLACS, COM3D
5th European Review Meeting on Severe Accident Research (ERMSAR-2012) Cologne (Germany), March 21-23, 2012
2
1. INTRODUCTION In case of severe accident in a light water nuclear reactor, hydrogen would be produced during reactor core degradation and released into the reactor building. This could subsequently raise the potential of a combustion hazard. A local ignition of the combustible mixture may generate standing flames or initially slow propagating flames. Depending on geometry, mixture composition and turbulence level the flame can accelerate or be quenched after a certain distance. The loads generated by the combustion process (increase of the containment atmosphere pressure and temperature) may threaten the integrity of the containment building and of internal walls and equipments. Turbulent deflagration flames may generate high pressure pulse, temperature peaks, large pressure gradients and even shock waves, which could seriously damage specific containment components, internal walls and/or safety equipment. The evaluation of such loads needs codes, which should be used with a high level of confidence. Even if flame acceleration has been largely studied for a homogeneous hydrogen distribution, only very few detailed data are available on the effect of turbulence on the H2/air flame propagation. These topics are addressed in the ENACCEF facility operated by CNRS in the frame of collaboration with IRSN. Three ENACCEF tests were delivered to the SARNET community in order to perfom a benchmark exercise in the frame of SARNET [1]. Blind and open phases had been organized. The aim of this paper is to present the results and outcomes of this benchmark.
2. ENACCEF EXPERIMENT ENACCEF is a vertical facility of about 5 m high and can be equipped with repeated obstacles in the bottom part. It is divided in 2 parts:
� the acceleration tube (3.2 m long and 154 mm i.d.), is equipped at its bottom-end with 2 tungsten electrodes as a low energy ignition device. At a distance of 1.9 m from the ignition point, 3 rectangular quartz windows (40 mmx300 mm optical path) are mounted flush with the inner surface, 2 of them are opposed to each other the third one being perpendicular to the others (see figure 1, right). These windows allow the recording of the flame front during its propagation along the tube using either a shadowgraph or a tomography system. The tube is also equipped with 11 small quartz windows (optical diameter: 8 mm, thickness: 3 mm) distributed along it.
� the dome (1.7 m long, 738 i.d.) is connected to the upper part of the acceleration tube via a flange. This part of the facility is also equipped with 3 silica windows (optical path: 170 mm, thickness: 40 mm), perpendicular to each other 2 by 2 (see figure1, left). Through these windows, the arrival of the flame can be recorded via a schlieren or a tomography system.
5th European Review Meeting on Severe Accident Research (ERMSAR-2012) Cologne (Germany), March 21-23, 2012
3
Figure 1: View of ENACCEF facility
Figure 2: ENACCEF instrumentation
To promote flame acceleration, 9 annular obstacles of blockage ratios (0.33 and 0.63) had been inserted in the acceleration tube. The first obstacle being 0.638 m from the ignition point and the distance between the obstacles was fixed to 0.154 m.
2.1. Instrumentation ENACCEF facility is highly instrumented to follow the flame propagation: 16 UV-sensitive photomultiplier tubes (HAMAMATSU, 1P28) are mounted across silica windows (optical diameter: 8 mm, thickness: 3 mm) in order to detect the flame as it propagates (5 photomultiplier tubes are located along the dome and 11 along the acceleration tube). Several high speed pressure transducers, (7 from CHIMIE METAL and 1 PCB) are mounted flush with the inner surface of the tube in order to monitor the pressure variation in the tube as the flame propagates and the pressure buildup is monitored via a PCB pressure transducer mounted at the ceiling of the dome. Moreover, gas sampling is used to measure the gas composition along the facility. 6 gas sampling are located along the acceleration tube and 1 on the dome. Figure 2 shows the sensors location along the facility height.
2.2. Gas Injection system The combustible mixtures were constituted of hydrogen distributed by Air Liquide (purity larger than 99.95 %) and laboratory dry compressed air. Before each run, the whole facility was vacuumed down below 1 Pa. Then, the mixture is introduced in ENACCEF via flow meter controllers (MKS1179A) at the desired composition up to a final pressure of 100 kPa. All the experiments were performed at ambient temperature.
2.3. Ignition system
The ignition point is located at 138 mm from the bottom of the facility. Ignition system is composed of two electrodes. The energy delivered is estimated to 100 mJ.
5th European Review Meeting on Severe Accident Research (ERMSAR-2012) Cologne (Germany), March 21-23, 2012
4
3. EXPERIMENTAL RESULTS
All the experiments reported here are performed at ambient temperature and at 100 kPa with the same initial gas composition (13%H2 + 87% air). Hence, the three experiments differ only with the used blockage ratio:
- Test RUN160 performed using smooth tube (without obstacle),
- Test RUN 158 performed using 9 annular rings of BR =0.33,
- Test RUN 153 performed with 9 annular rings of BR=0.63. To deduce the combustion completeness rate, gas composition had been measured before and after combustion for each test. These measurements show that the combustion is almost complete and the remaining hydrogen concentration is lower then 0.3%.
Moreover, flame position and pressure time evolution measurements show that:
� Flame propagates in quasi-laminar regime in case of smooth tube (RUN160) and between the ignition point and the first obstacle for RUN158 and RUN153 tests,
� pressure rise depends on turbulence level induced by obstacles,
� The pressure decrease after combustion is independent of obstacles,
� Flame acceleration depends on the blockage ratio.
The following figures show the flame position and pressure time evolution of the three
tests.
Effect of obstacles
Flame position
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
0,00 0,10 0,20 0,30 0,40
time (s)
position/ignition point (m)
RUN153-BR=0.63
RUN158-BR=0.33
1st obstacle
last obstacle
dome
RUN160-BR=0
Effect of obstacles
Totale pressure
0
1
2
3
4
5
6
0 0,2 0,4 0,6 0,8 1 1,2 1,4
time (s)
pressure (bar)
RUN158-BR=0.33
RUN153-BR=0.63
RUN160-BR=0
Figure3: flame position for tests RUN153, RUN158 and RUN160
Figure4: pressure time evolution for tests RUN153, RUN158 and RUN160
5th European Review Meeting on Severe Accident Research (ERMSAR-2012) Cologne (Germany), March 21-23, 2012
5
4. COMPARISON OF CALCULATION TO EXPERIMENTS
4.1. Participants, organizations and codes Seven organizations provided eight blind and open calculations. Four computer programs were used, one of the Lumped parameter (LP) type and three of the computational fluid dynamics (CFD) type. The following table presents the participants list and the used codes:
Participant Affiliation Program Type Blind/open Chaumeix CNRS-ICARE Experiment
Kostka NUBIKI ASTEC LP Blind/open
Hyung Seok & Sang Baek
KAERI CFX CFD Blind/open
Schramm GRS CFX CFD Blind/open
Hohner GRS ASTEC LP Blind/open
Movahed AREVA COM3D CFD Blind (test RUN153, RUN158) /open
Povilaitis LEI ASTEC LP Blind/open
Brähler RUB ASTEC LP Blind/open
Bleyer & Bentaib
IRSN Flacs CFD open
Table 1: List of the used codes
The used codes and the corresponding combustion models are briefly described below:
ASTEC CPA-FRONT model
ASTEC is a complex system of codes for reactor safety assessment. For this SARNET Benchmark, only the CPA (Containment Part of ASTEC) module is used. CPA is a lumped parameter code. While energy and mass conservation is respected, the momentum balance is neglected. All ASTEC contributions were made using CPA-FRONT combustion model. This model calculates the flame front burning velocity in case of hydrogen combustion and regulates the propagation of the flame from zone to zone (it especially signalizes when an adjacent zone is to ignite). Its main purpose is an easy applicability for containment simulations, hence it is designed in a way that no additional input parameters are required apart from the “usual” thermohydraulic CPA input deck. It shall enable the user to take into account and to calculate hydrogen combustion at least roughly in his simulation without much effort. In FRONT, the flame propagation is modelled inside the junctions. The H2-combustion itself (mass transfer from H2 and O2 to steam, distribution of combustion heat) takes place in the zones.
CFX BVM model
KAERI and GRS use ANSYS CFX 11 which solves the Navier-Stokes equations. They selected the SST turbulence model. In order to model combustion a turbulent flame closure (Zimont correlation) is used.
5th European Review Meeting on Severe Accident Research (ERMSAR-2012) Cologne (Germany), March 21-23, 2012
6
COM3D model
AREVA uses COM3D, which solves the Navier-Stokes equations. The standard K-epsilon turbulence model was selected and eddy break-up (EBU) model with Said-Borghi extension is applied for turbulent combustion modelling.
FlACS combustion model
FLACS contains a combustion model that assumes that the flame in an explosion can be regarded as a collection of flamelets. One-step reaction kinetics is assumed, with the laminar burning velocity being a measure of the reactivity of a given mixture. The combustion model consists of two parts: a flame model and a burning velocity model. The
β-flame model gives the flame a constant flame thickness equal to 3-5 grid cells, and assures that the flame propagates into the reactant with the specified velocity. A flame folding model has also been implemented to represent flame folding around sub-grid obstacles. The following table summarizes the peculiarity of each used code:
AREVA GRS KAERI IRSN GRS/LEI/RUB/ NUBIKI
Code name COM3D 2.2 CFX CFX FLACS ASTEC
Turbulence model
k-ε SST SST k-ε Correlation
Combustion model
EBU extended BVM BVM Beta-flame model
CPA-FRONT
Convective heat losses
- + + + +
Radiation model
- + Discrete Transfer
- +
Table 2 : Summary of used models (- means not used ; + for used)
4.2. Blind benchmark calculations
4.2.1. Nodalization For ASTEC LP nodalizations, the acceleration tube was modelled using cells sizes of 115 mm diameter. The dome was modeled using 1 cell in Nubiki calculation and using 10 layers for the other contributions. The main geometric data are summarised in the following table:
5th European Review Meeting on Severe Accident Research (ERMSAR-2012) Cologne (Germany), March 21-23, 2012
7
RUB GRS NUBIKI LEI
Total number of nodes
52 52 24 41
Sketch of the used nodalization
733
154
33
00
15
40
3086
2932
2624
2316
1700
1392
1084
776
468
3300
160116
2080
3608
4224
3916
4532
4840
AA
ignition point
A
A
Table3: ENACCEF nodalisation for ASTEC contributions For CFD contributions, several strategies had been adopted by considering quarter, half or full volume. The following table summarizes the main characteristic of the mesh used by GRS, KAERI, AREVA and IRSN.
GRS KAERI AREVA IRSN
Type of mesh 1/4 1/2 Full Full
Total number of nodes
524 000 -Acceleration Tube: 2,267,634 hexahedral cells -Dome: 823,860 hexahedral cells
950616 Cubic cells Cell size 1.54 cm BR=0.571 (Test 153) BR=0.381 (Test 158)
1022625
Mesh type Structured
Structured
Structured
Structured With porosity
Table 4: ENACCEF nodalisation for CFD contributions
5th European Review Meeting on Severe Accident Research (ERMSAR-2012) Cologne (Germany), March 21-23, 2012
8
4.2.2. Blind calculations
As mentioned previously, the experimental results show a mostly complete combustion and
a quasi-laminar propagation regime before the first obstacle. We observe also that
pressure rise depends on turbulence level induced by obstacles and pressure decrease after
combustion is independent of obstacles. So the comparison of code calculations to
experiment will be focused on these points.
RUN 153 (BR=0.63)
� Pressure time evolution and combustion completeness
Totale pressure -Test BR =0,63
0
1
2
3
4
5
6
0
time (s)
Pressure (bar)
experiment
NUBIKI-ASTEC bar
GRS-ASTEC
GRS-CFX
KAERI-CFX
RUB-ASTEC
LEI-ASTEC
AREVA-COM3D
Figure 5: pressure time evolution-comparison calculation -experiments Figure 5 shows the experimental and calculated pressure time evolutions at the PCB1 pressure transducers in upper part of the acceleration tube. The experimental curve shows a first pressure peak around 2.5 bar at time 0.109 s corresponding to flame position between last obstacle and the dome entrance. This first pressure peak was predicted by almost all contributions, except RUB-ASTEC. However, the magnitude of the peak is overestimated in GRS-ASTEC and GRS-CFX contributions. This is mainly du to the fact that these contributions overestimated the flame speed in the acceleration tube (see Fig. 7). Moreover, the pressure increase starts when the flame reaches the dome area. The maximum pressure value is 4.98 bars and the pressure rise (dp/dt) is around 142 bar/s. After combustion, the pressure decreases due to heat losses with a slop of -2.7 bar/s. From Fig. 5, we can observe that the pressure rise is quite well predicted by all contributions except LEI-ASTEC. However, the pressure decrease due to heat losses is underestimated by all codes. Furthermore, combustion completeness rate could be deduced from pressure data by comparing the calculated pressure maximum value to the pressure experimental maximum
value PexpMax as follow:( )
MaxP
PMaxPCompRate
exp
maxexp −= . For RUN 153 test, PexpMax is
equal to 4,98bars.
5th European Review Meeting on Severe Accident Research (ERMSAR-2012) Cologne (Germany), March 21-23, 2012
9
The following table presents completeness combustion rate for each contribution:
GRS-ASTEC
GRS-CFX
NUBIKI-ASTEC
LEI-ASTEC
RUB-ASTEC
KAERI-CFX
AREVA COM3D
Pmax 5,0015 5,3535 4,924731 4,565989 5,2959 3,9148 4.94
(PexpMax-PMax)/ PexpMax -0,0032 -0,073 0,0121 -0,084 -0,062 0,214 0.008
Table 5: combustion completeness rate evaluation
From the table 5, we can conclude all contributions, except KAERI-CFX, predict quite well the combustion completeness rate.
� Flame position in the acceleration tube
The calculated and measured flame position in the acceleration tube are presented and
compared in the following figure:
RUN153 : Flame position
0
0,5
1
1,5
2
2,5
3
0 0,01 0,02 0,03 0,04 0,05 0,06
Time of Flame Arrival (s)
Elevation (m)
experiment
NUBIKI-ASTEC
GRS-CFX
GRS-ASTEC
KAERI-CFX
LEI-ASTEC
RUB-ASTEC
AREVA-COM3D
Figure 6: RUN153-flame position
From this figure and as mentioned previously, three flame propagation phases could be
distinguished:
� 1st Phase corresponds to the flame propagation between the ignition point and the
first obstacle. During this phase, the flame propagates in a smooth tube with mean
velocity of 14 m/s. From the calculation flame position, we can conclude that the
flame velocity in this area is overestimated by all contribution, except KAERI-CFX
who underestimates it. During this phase, flame speed could be influenced by the
delivered ignition energy. To limit this effect, we skip the phase corresponding to
the flame propagation from the ignition point to the first PM sensor. Consequently,
the corresponding time duration is skipped from calculations and experiment curves
as shown in the following figure:
5th European Review Meeting on Severe Accident Research (ERMSAR-2012) Cologne (Germany), March 21-23, 2012
10
RUN153 : Flame position
0
0,01
0,02
0,03
0,04
0,05
0,06
0 0,5 1 1,5 2 2,5 3Elevation (m)
Time of Flame Arrival (s)
experiment
NUBIKI-ASTEC
GRS-CFX
GRS-ASTEC
KAERI-CFX
LEI-ASTEC
RUB-ASTEC
AREVA-COM3D
RUN153 : Flame velocity
0
100
200
300
400
500
600
700
800
0 0,5 1 1,5 2 2,5 3Elevation (m)
Flame velocity (m/s)
experiment
NUBIKI-ASTEC
GRS-CFX
GRS-ASTEC
KAERI-CFX
LEI-ASTEC
RUB-ASTEC
AREVA-COM3D
Figure 7: RUN153-flame position with time
shift Figure 8: RUN153-flame velocity
In Figure 7, all flame position curves start at PM16 and at time t=0s. With this time
shifting, we observe that flame position is quite well predicted by GRS-ASTEC,
RUB-ASTEC and NUBIKI-ASTEC. However, GRS-CFX and KAERI-CFX underestimates
respectively overestimates the flame arrival time during this phase.
� 2nd Phase corresponds to flame propagation in the area between the first and the
last obstacle. Due to turbulence induced by those obstacles, the flame speed
increases and reaches 500m/s. As shown in Fig. 8, GRS-CFX, GRS-ASTEC and RUB-
ASTEC predicted reasonably well the flame acceleration in this area.
� 3rd Phase corresponds to the flame propagation in the area between the last
obstacle and the dome entrance. In this phase and due to the decrease of
turbulence level, flame speed decreases from 500m/s to 366m/s. This phase is
reasonably well described by GRS-ASTEC.
� 4th Phase correspond to the flame propagation in the dome area. During this phase,
flame behaves as reactive turbulent jet: the flame propagates first in the upward
direction before radial propagation. For these reasons, the measured flame position
and velocity are not relevant for code-experiment comparison.
5th European Review Meeting on Severe Accident Research (ERMSAR-2012) Cologne (Germany), March 21-23, 2012
11
RUN 158(BR=0.3)
� Pressure time evolution and combustion completeness
RUN 158
0
1
2
3
4
5
6
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1
time (s)
Pressure (bar)
experiment
AREVA-COM3D
NUBIKI-ASTEC
GRS-CFX
KAERI-CFX
LEI-ASTEC
RUB-ASTEC
GRS-ASTEC
Figure 9: RUN158-pressure time evolution
Figure 9 shows the experimental and calculated pressure time evolutions. The experimental curve shows a first pressure peak around 1.9 bar at time 0.118 s corresponding to flame position between last obstacle and the dome entrance. This first pressure peak was predicted by almost all contributions, except RUB-ASTEC. However, the magnitude of the peak is overestimated in GRS-ASTEC and GRS-CFX contributions. This is mainly du to the fact that these contributions overestimated the flame speed in the acceleration tube (see Fig. 11). Moreover, the pressure increase starts when the flame reaches the dome area. The maximum pressure value is 5.07 bars and the pressure rise (dp/dt) is around 137 bar/s. After combustion, the pressure decreases due to heat losses with a slop of -2.7 bar/s. From Fig. 9, we can observe that the pressure rise is quite well predicted by all contributions except LEI-ASTEC. However, the pressure decrease due to heat losses is underestimated by all codes. Furthermore, the combustion completeness rate had been deduced from pressure values as for RUN 153. The obtained results are presented in the following table:
GRS-ASTEC
GRS-CFX
NUBIKI-ASTEC
LEI-ASTEC
RUB-ASTEC
AREVA-COM3D
KAERI-CFX
Pmax 5.0626 5.038 4.4518 4.3985 5.303 5.2209 4.3867
(PexpMax-PMax)/PexpMax
-0,0015 -0,006 -0,122 -0,1325 0.045 0.029 -0.134
Table 6: combustion completeness rate evaluation
From the table 6, we can conclude all contributions, except KAERI-CFX, predict quite well the combustion completeness rate.
5th European Review Meeting on Severe Accident Research (ERMSAR-2012) Cologne (Germany), March 21-23, 2012
12
� Flame position in the acceleration tube
Calculated and the measured flame position in the acceleration tube are presented and
compared in the following figure where the curves are shifted as for test RUN153.
RUN158 : Flame velocity
0
100
200
300
400
500
600
0 0,5 1 1,5 2 2,5 3Elevation (m)
Flame velocity (m/s)
experiment
NUBIKI-ASTEC
GRS-CFX
GRS-ASTEC
KAERI-CFX
LEI-ASTEC
RUB-ASTEC
AREVA
Figure 10: RUN158-flame position
Figure 11: RUN158-flame position
From the previous figures and as for RUN153, flame propagation into the acceleration tube
shows three main phases:
� 1st Phase corresponds to the flame propagation between the first PM sensor and the
first obstacle. During this phase, NUBIKI-ASTEC predicts quite well the flame
position. However, GRS-CFX, RUB-ASTEC and LEI-ASTEC underestimate slightly the
time duration while GRS-ASTEC, AREVA-COM3D and KAERI-CFX overestimate it.
� 2nd Phase corresponds to flame propagation in the area between the first and the
last obstacle. As shown in Fig.11, GRS-CFX and AREVA-COM3D predicted reasonably
well the flame acceleration in this area. However, GRS-ASTEC and RUB-ASTEC
overestimate this acceleration where NUBIKI-ASTEC and LEI-ASTEC underestimate
it.
� 3rd Phase corresponds to the flame propagation in the area between the last
obstacle and the dome entrance. In this phase and due to the decrease of
turbulence level, flame speed decreases from about 350 m/s to about 200 m/s. This
phase is reasonably well described by AREVA-COM3D, GRS-CFX and GRS-ASTEC.
5th European Review Meeting on Severe Accident Research (ERMSAR-2012) Cologne (Germany), March 21-23, 2012
13
RUN 160(BR=0)
� Pressure time evolution and combustion completeness
RUN 160
0
1
2
3
4
5
6
0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5
time (s)
pressure (bar)
experiment
NUBIKI-ASTEC bar
GRS-CFX
GRS-ASTEC
KAERI-CFX
LEI-ASTEC
RUB-ASTEC
Figure 12: RUN160-pressure time evolution As the acceleration tube is smooth, only one pressure peak due to the combustion in the dome is observed in pressure curves presented in figure 12. Nevetheless, pressure peak numerical results show a large discrepancy.
GRS-ASTEC
GRS-CFX
NUBIKI-ASTEC
LEI-ASTEC
RUB-ASTEC
KAERI-CFX
Pmax 4.24 4.5 4.12 4.46 5.26 nc
(PexpMax-PMax)/ PexpMax
0.09 0.04 0.125 0.05 -0.11 nc
Table 7: combustion completeness rate evaluation From table 7, we can conclude all contributions, except KAERI-CFX, RUB-ASTEC and NUBIKI-ASTEC, predict quite well the combustion completeness rate.
� Flame position in the acceleration tube
Calculated flame position in the acceleration tube and the measured flame position are
presented and compared in the following figure:
5th European Review Meeting on Severe Accident Research (ERMSAR-2012) Cologne (Germany), March 21-23, 2012
14
RUN160 : Flame position
0
0,3
0,6
0,9
1,2
1,5
0 0,5 1 1,5 2 2,5 3Elevation (m)
Time of Flame Arrival (s)
experiment
NUBIKI-ASTEC
GRS-CFX
GRS-ASTEC
KAERI-CFX
LEI-ASTEC
RUB-ASTEC
-58,7ms
-95,3ms
-31,7ms
-51,9ms
-46,5ms
-16,2ms
-54ms
RUN160 : Flame velocity
0
10
20
30
40
50
60
70
0 0,5 1 1,5 2 2,5 3Elevation (m)
Flame velocity (m/s)
0
100
200
300
400
500
600
700
experiment
NUBIKI-ASTEC
GRS-CFX
GRS-ASTEC
LEI-ASTEC
KAERI-CFX
RUB-ASTEC
Figure 13: RUN160-flame position
Figure 14: RUN160-flame position
Figures 13 and 14 show flame locations increase “quasi- linearly” with time. The
correspond flame speed average is estimated to 14 m/s. This behaviour is quite well
predicted by KAERI-CFX and LEI-ASTEC. RUB-ASTEC overestimate this velocity where GRS-
CFX and GRS-ASTEC underestimate it.
4.2.3. Open calculations
Open calculations had been performed by the participants by using different input
parameter. The main changes for LP contributions concern parameters dealing with the
initial turbulence level. Concerning CFD contributions, the changes concern the use of
refined meshes. The following figures compare blind and open results based on the
pressure time evolution.
RUN BR=33%
0
1
2
3
4
5
6
0 0,1 0,2 0,3 0,4
Time (s)
Pressure (bar)
experiment
NUBIKI-ASTEC
GRS-ASTEC
KAERI-CFX
RUB-ASTEC
IRSN-FLACS
Totale pressure -Test BR =0,63
0
1
2
3
4
5
6
0
time (s)
Pressure (bar)
experiment
NUBIKI-ASTEC bar
GRS-ASTEC
GRS-CFX
KAERI-CFX
RUB-ASTEC
LEI-ASTEC
AREVA-COM3D
Figure 15: RUN153-open phase
Figure 16: RUN153-blind phase
5th European Review Meeting on Severe Accident Research (ERMSAR-2012) Cologne (Germany), March 21-23, 2012
15
RUN BR=63%
0
1
2
3
4
5
6
0 0,05 0,1 0,15 0,2 0,25 0,3Time (s)
Pressure (bar)
experiment
NUBIKI-ASTEC
GRS-CFX
GRS-ASTEC
KAERI-CFX
LEI-ASTEC
RUB-ASTEC
RUN 158
0
1
2
3
4
5
6
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1
time (s)
Pressure (bar)
experiment
AREVA-COM3D
NUBIKI-ASTEC
GRS-CFX
KAERI-CFX
LEI-ASTEC
RUB-ASTEC
GRS-ASTEC
Figure 17: RUN158-open phase
Figure 18: RUN158-blind phase
RUN160 BR=0%
0
1
2
3
4
5
0 0,2 0,4 0,6 0,8 1 1,2 1,4
Time (s)
Pressure (bar)
experiment
NUBIKI-ASTEC
GRS-ASTEC
KAERI-CFX
LEI-ASTEC
RUB-ASTEC
IRSN-FLACS
RUN 160
0
1
2
3
4
5
6
0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5
time (s)
pressure (bar)
experiment
NUBIKI-ASTEC bar
GRS-CFX
GRS-ASTEC
KAERI-CFX
LEI-ASTEC
RUB-ASTEC
Figure 19: RUN160-open phase
Figure 20: RUN160-blind phase
5. Conclusion
In Framework of SARNET2 project, combustion benchmark had been organized within eight contributions from seven organizations. Blind and open simulation results from three CFD codes CFX, COM3D and FLACS and ASTEC LP code have been compared against ENACCEF experimental results. The comparison shows that most of those codes are able to predict pressure time evolution and the flame speed during the acceleration phase. Nevertheless, the flamespeed maximum value is generally overpredicted. This indicates that there are still limitations and weaknesses in the combustion models used in the different codes. Up to now it is not clear, if the limitations are in the chemistry part or in the turbulent combustion model or in the coupling between the two. Therefore further investigations are needed, also because scaling remains an open issue. All experiments presented in this paper are performed without steam. Since in the plant application analyses always steam exists at the start of combustion analyses, it is recommended to prove the applicability and reliability of the codes in presence of the steam with appropriate experiment like ENACCEF tests with diluent for a benchmark exercise in the frame of SARNET [2] investigating the effect of diluent on flame propagation.
6. REFERENCES [1] Bentaib, A.,and Chaumeix N., SARNET H2 Combustion Benchmark Specification of ENACCEF test-Turbulence effect on flame propagation, RAPPORT DSR/SAGR N° 102 [2] Bentaib, A.,and Chaumeix N., SARNET H2 Combustion Benchmark Specification of ENACCEF test-Diluent effect on flame propagation, RAPPORT DSR/SAGR N° 206