VALIDATING FDS AGAINST A LARGE-SCALE FIRE TEST FOR FACADE SYSTEMS

Markus Nilsson, Johan Nilsen and Axel Mossberg
Brandskyddslaget AB Consulting firm, Sweden

Introduction

Background

  • Part of an MSc thesis at Lund University
  • Need of a calculation tool for modelling external fire spread
  • Evaluating the tool before performing the following analysis
  • Previous numerical work on a large-scale fire test showed promising results
  • SP FIRE 105 facade test - modified test
  • An update in FDS $\neq$ every area is improved
  • Investigate possible differences in the program versions
    (FDS 6.2.0 vs FDS 5.5.3)

Experimental setup

Modified SP FIRE 105 test rig

Namnlös1

Fire development

Figure1-2ny

Setup in FDS

Figure4

Processing the output data

$\dot{q}^{\prime\prime}_{IRHF}$ from the fire test

(1)
\[ \dot{q}^{\prime\prime}_{inc} = \sigma T_{s}^{4} - \dfrac{h_{c}(T_{g}-T_{s})}{\epsilon} + \dfrac{dc\rho}{\epsilon} \cdot \dfrac{dT}{dt} \]
(2)
\[ h_{c} = 2.4 T_{f}^{0.085} \cdot u_{\infty}^{1/2} \cdot x^{-1/2} \]
(3)
\[ \dot{q}^{\prime\prime}_{inc} = \dot{q}^{\prime\prime}_{IRHF} \]

$\vspace{\baselineskip}$

$\epsilon_{PT} \dot{q}^{\prime\prime}_{inc} - \epsilon_{PT} \sigma T_{PT}^{4} + h_{PT} (T_{g} - T_{PT}) + K(T_{g} - T_{PT})$

$= C \dfrac{dT_{PT}}{dT}$

$\vspace{\baselineskip}$

$T_{PT} \sim T_{AST}$

$\dot{q}^{\prime\prime}_{IRHF}$ in FDS

(4)
\[ \dot{q}^{\prime\prime}_{inc} = \dfrac{\dot{q}^{\prime\prime}_{rad}}{\epsilon} + \sigma T_{w}^{4} + \dot{q}^{\prime\prime}_{c} \]
(5)
\[ \dot{q}^{\prime\prime}_{rad} = \dot{q}^{\prime\prime}_{rad, in} - \dot{q}^{\prime\prime}_{rad, out} = \dot{q}^{\prime\prime}_{rad, in} - \epsilon \sigma T_{w}^{4} \]
(6)
\[ \dot{q}^{\prime\prime}_{inc} = \dfrac{\dot{q}^{\prime\prime}_{rad, in}}{\epsilon} + \dot{q}^{\prime\prime}_{c} \]
(7)
\[ \dot{q}^{\prime\prime}_{IRHF} = \dot{q}^{\prime\prime}_{inc} - \dot{q}^{\prime\prime}_{c} = \dfrac{\dot{q}^{\prime\prime}_{rad, in}}{\epsilon} \]

Results

Grid sensitivity, thermocouples

Figure9

Grid sensitivity, thermometers

Figure10

Grid sensitivity, $T_{AST}$

Figure11

Facade damage

facadedamage

Grid sensitivity, $\dot{q}^{\prime\prime}_{IRHF}$

Figure12

FDS 6.2.0 vs FDS 5.5.3

FDS 6.2.0 vs FDS 5.5.3, temperature

Figure14

FDS 6.2.0 vs FDS 5.5.3, $\dot{q}^{\prime\prime}_{IRHF}$

Figure15

Conclusions

  • FDS 6.2.0 generally produce higher temperatures and $\dot{q}^{\prime\prime}_{IRHF}$ for the given setup compared to FDS 5.5.3
  • FDS 6.2.0 produce results that are more in line with the test results compared to FDS 5.5.3
  • To obtain credible results particularly close to the fire, a mesh resolution $D^{*}/\delta x$ of at least 30 is needed.
  • Plenty of heat flux outputs in FDS – inadequate descriptions – confusing for the ordinary FDS-user
  • $T_{AST}$ can be used as an alternative means of expressing the thermal exposure to a surface in FDS

Thank you for listening