Large-Scale Tunnel Fire Tests and the use of CFD modelling to predict Thermal Behaviour _Gabriele_Vigne_151009

7/31/2019 Large-Scale Tunnel Fire Tests and the use of CFD modelling to predict Thermal Behaviour _Gabriele_Vigne_151009

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Experimental Research - Large-Scale TunnelFire Tests and the use of CFD Modelling to

predict Thermal Behavior

Gabriele Vigne16 October 2009

Fire Protection and Life Safety in Buildings and Transportation Systems , Santander 16 October 2009


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Presentation

Introduction

The Tests

The Models

Results and Future Works



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Introduction

-Arup Fire in Madrid forms part of a European constructionTechnology Platform (ECTP)

- Test series were conducted in La Ribera del Folgoso (Spain) in a

50m cross section tunnel during March 2009

- Similar tests were conducted in 2008 and the results have been

considered when realizing these tests



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The Tests

Five tests were conducted in the tunnel,

each one with the same configuration and

external conditions in order to quantify the

uncertainty of the experimentalmeasurements.

Fire Size: 5-6 MW

Duration: 8 minutes

Ventilation :


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Geometry

- Cross Section Area of 50m

- 100m Length

- Concrete surface



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The Fire

A metal containers designed to achieve a

Fire Power of 5-6MW

Dimension: 2.0m x 1.00m

The container was filled with a thin layer of

water and a layer of Heptane



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1.0000

6.5005.5000

4.00

1.5000

2.0002.5000

3.5000

2.50

2.50

1.0000

1.0000

4.00

2.0000

1.0000

2.0000

2.0000

5.0000

2.0000

2.0000

2.0000

2.0000

2.0000

2.0000

5.0000

8.0000

Instrumentation

Thermocouples were placed at ceiling height along the tunnel, every

2m from the fire and through the fire plume

Four couple of plate thermometers were placed 4m from the fire at a

height of 2.5m and 3.5m.

Two velocimeters were positioned 5m from the fire to ensure that lowvelocities were maintained at the start of each test.



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Models Setup

3 simple Models were run, each one with a different grid resolution

40

20

10

D*/x

9

5

3

Totalnumber of

meshes

0.10.05FDS 3

0.20.1FDS 2

X0.20.2FDS 1

Recommendedvalue

Resolutionof the other

meshes (m)

Resolutionof the Fire

mesh (m)

Modelname


Assuming a 5.5MW fire => D*=2.0


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The Model

-Software used: FDS 5.3.1

- HRR: from test data

- Reaction: heptane

- Walls: concrete, thermally thick

- THCPs modelled as thermocouples

- Velocity: none



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Results


-Temperature

Above the fire plume FDS has a tendency to heavily over predict the temperatures, once outside the

plume the temperatures are closer to the measured temperatures.


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Results

-Temperature

It is difficult to capture the correct temperature above the plume due to the continuous fluctuation of

the flame.

For this reason it is very difficult to draw valid conclusions about the temperature of the thermocouple

placed above the fire.



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Results

Heat Release Rate

HRR from mass loss measurements was close towhat expected from empirical pool-fire calculations

The fuel was burning consistently for 5 minutes



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Results

The combination of the experimental uncertainty associated with both the model input

parameters and the measured model outputs served as a benchmark for evaluation of the

models

A range of 10% was obtained as result of the experiments.



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Results

Measured vs. predicted gas temperature, 2m from the fire



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Results




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Results




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Results




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Plate Thermometers

Due to the quantity of Heptane available during the tests and the wish

to perform as many tests as possible, the time allowed to the pool fire

to burn consistently was limited to about 5 minutes. Because of the

thermal inertia of the plate thermometers, the duration of the fire didnot permitted the plate thermometers to reach steady state conditions

during the tests as can be seen in the graph below.



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Conclusions

-FDS has shown a good performance in predicting the temperature magnitudeinside the tunnel

-The evaluation showed the importance of using a correct grid resolution to

get reliable results. This is very important it should be assured that a proper

grid resolution always is to be used.

- To be able to fully investigate and analyse the heat flux behaviour it isnecessary with longer burning times.



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Further Works

The duration of the fire was enough to reach steady state condition for the

normal thermocouples whilst it was not possible for the plate

thermometers

The FDS model was deliberately built in a simple way as it would have

been created by an average user; further adjustments to the FDS model

could lead to better results

Additional tests will be performed in order to investigate the heat flux

behaviour around the fire.



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Acknowledgement

-Fundacin Santa Barbara

- NIST, VTT



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Gabriele Vigne16 October 2008

Thanks


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Large-Scale Tunnel Fire Tests and the use of CFD modelling to predict Thermal Behaviour _Gabriele_Vigne_151009