Ermsa2012rBenchEnaccef1 PK Areva comment 2012 01 Hohner GRS ASTEC LP Blind/open ... (mass transfer from H 2 and O 2 to steam, ... March 21-23, 2012 6 COM3D model AREVA uses COM3D,

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


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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.


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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.


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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


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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.


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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:


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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


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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.


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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:


10


0

0,01

0,02

0,03

0,04

0,05

0,06

0 0,5 1 1,5 2 2,5 3Elevation (m)


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.


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RUN 158(BR=0.3)


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.


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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.


0

100

200

300

400

500

600

0 0,5 1 1,5 2 2,5 3Elevation (m)


experiment

NUBIKI-ASTEC

GRS-CFX

GRS-ASTEC

KAERI-CFX

LEI-ASTEC

RUB-ASTEC

AREVA



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.


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RUN 160(BR=0)


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.


Calculated flame position in the acceleration tube and the measured flame position are

presented and compared in the following figure:


14


0

0,3

0,6

0,9

1,2

1,5

0 0,5 1 1,5 2 2,5 3Elevation (m)


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


0

10

20

30

40

50

60

70

0 0,5 1 1,5 2 2,5 3Elevation (m)


0

100

200

300

400

500

600

700

experiment

NUBIKI-ASTEC

GRS-CFX

GRS-ASTEC

LEI-ASTEC

KAERI-CFX

RUB-ASTEC



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


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



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



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

Documents

Ermsa2012rBenchEnaccef1 PK Areva comment 2012 01 Hohner GRS ASTEC LP Blind/open ... (mass transfer from H 2 and O 2 to steam, ... March 21-23, 2012 6 COM3D model AREVA uses COM3D,