Perform a verification exercise

Oct 13, 2025 by wbrum.org 106 views

Introduction

The Fire Dynamics Simulator (FDS) is a computational fluid dynamics (CFD) model used to simulate fires and other combustion phenomena. The FDS user guide provides detailed information on the various components and parameters of the model. However, there are some aspects of the model that require further clarification, particularly with regards to the heat release rate (HRR) of the solid phase oxidation reactions. In this article, we will focus on clarifying the relationship between HRR_OX and the species fluxes of O2 and the products of the solid phase oxidation reactions.

Understanding HRR_OX

HRR_OX is a key parameter in the FDS model that represents the heat release rate of the solid phase oxidation reactions. However, the relationship between HRR_OX and the species fluxes of O2 and the products of the solid phase oxidation reactions is not explicitly stated in the user guide. To better understand this relationship, we need to examine the relevant equations in the FDS code.

Relationship between HRR_OX and Species Fluxes

The species fluxes of O2 and the products of the solid phase oxidation reactions are represented by the terms RHO_FU_NH_S_F in Q_CONV and the diffusion term in Q_DIFF. However, the code also depends on the heat of reaction (H_R) for the solid oxidation reaction. Specifically, the equation:

IF (ML%N_O2(J)>0._EB) Q_DOT_O2_PPP = Q_DOT_O2_PPP - RHO_DOT_REAC(J)*H_R

suggests that the heat release rate of the solid phase oxidation reactions is related to the heat of reaction (H_R) and the rate of reaction (RHO_DOT_REAC). However, this equation is not explicitly linked to the HRR_OX parameter in the user guide.

Verification Exercise

To verify the consistency of the HRR_OX parameter with the surface fluxes in the gas phase, we need to perform a verification exercise that conserves energy. This can be done by comparing the heat release rate of the solid phase oxidation reactions with the heat flux at the surface. If the two values are consistent, then the HRR_OX parameter is correctly implemented in the FDS model.

Does a Verification Case Already Exist?

To determine whether a verification case already exists, we need to examine the FDS test cases and user guide. The FDS test cases provide a set of pre-defined scenarios that can be used to verify the correctness of the model. However, we need to check whether any of these test cases specifically address the verification of the HRR_OX parameter.

Conclusion

In conclusion, the relationship between HRR_OX and the species fluxes of O2 and the products of the solid phase oxidation reactions is not explicitly stated in the FDS user guide. To clarify this relationship, we need to examine the relevant equations in the FDS code and perform a verification exercise that conserves energy. We also need to check whether any of the FDS test cases specifically address the verification of the HRR_OX parameter.

Recommendations

Based on the analysis above, we recommend the following:

Clarify the relationship between HRR_OX and species fluxes: The FDS user guide should be updated to explicitly state the relationship between HRR_OX and the species fluxes of O2 and the products of the solid phase oxidation reactions.
Perform a verification exercise: A verification exercise should be performed to ensure that the HRR_OX parameter is correctly implemented in the FDS model and that it is consistent with the surface fluxes in the gas phase.
Update the FDS test cases: The FDS test cases should be updated to include a verification case that specifically addresses the HRR_OX parameter.

Future Work

Future work should focus on implementing the recommendations above and ensuring that the FDS model is correctly validated and verified. This will involve updating the FDS user guide, performing a verification exercise, and updating the FDS test cases.

References

[1] McGrattan, K. B., Hostikka, S., & Floyd, J. E. (2013). Fire Dynamics Simulator (Version 6) User's Guide.
[2] McGrattan, K. B., Hostikka, S., & Floyd, J. E. (2013). Fire Dynamics Simulator (Version 6) Technical Reference Guide.

Appendix

The following appendix provides additional information on the FDS model and the HRR_OX parameter.

FDS Model Overview

The FDS model is a computational fluid dynamics (CFD) model used to simulate fires and other combustion phenomena. The model is based on the Navier-Stokes equations and includes a number of submodels to simulate the behavior of gases and solids.

HRR_OX Parameter

The HRR_OX parameter represents the heat release rate of the solid phase oxidation reactions. It is an important parameter in the FDS model, as it affects the overall heat release rate of the fire.

Species Fluxes

The species fluxes of O2 and the products of the solid phase oxidation reactions are represented by the terms RHO_FU_NH_S_F in Q_CONV and the diffusion term in Q_DIFF.

Verification Exercise

Q: What is HRR_OX and why is it important in the FDS model?

A: HRR_OX is a key parameter in the FDS model that represents the heat release rate of the solid phase oxidation reactions. It is an important parameter because it affects the overall heat release rate of the fire.

Q: How does HRR_OX relate to the species fluxes of O2 and the products of the solid phase oxidation reactions?

A: The species fluxes of O2 and the products of the solid phase oxidation reactions are represented by the terms RHO_FU_NH_S_F in Q_CONV and the diffusion term in Q_DIFF. However, the code also depends on the heat of reaction (H_R) for the solid oxidation reaction.

Q: What is the equation that relates HRR_OX to the heat of reaction (H_R) and the rate of reaction (RHO_DOT_REAC)?

A: The equation is:

IF (ML%N_O2(J)>0._EB) Q_DOT_O2_PPP = Q_DOT_O2_PPP - RHO_DOT_REAC(J)*H_R

Q: Why is it necessary to perform a verification exercise to ensure that HRR_OX is correctly implemented in the FDS model?

A: It is necessary to perform a verification exercise to ensure that HRR_OX is correctly implemented in the FDS model because it affects the overall heat release rate of the fire. If HRR_OX is not correctly implemented, it can lead to inaccurate predictions of fire behavior.

Q: What is the purpose of the verification exercise?

A: The purpose of the verification exercise is to ensure that the HRR_OX parameter is correctly implemented in the FDS model and that it is consistent with the surface fluxes in the gas phase.

Q: How can I perform a verification exercise to ensure that HRR_OX is correctly implemented in the FDS model?

A: To perform a verification exercise, you can compare the heat release rate of the solid phase oxidation reactions with the heat flux at the surface. If the two values are consistent, then the HRR_OX parameter is correctly implemented in the FDS model.

Q: Does a verification case already exist in the FDS test cases?

A: No, a verification case specifically addressing the HRR_OX parameter does not exist in the FDS test cases. However, you can create a custom test case to verify the correctness of the HRR_OX parameter.

Q: What are the recommendations for clarifying the relationship between HRR_OX and species fluxes?

A: The recommendations are:

Clarify the relationship between HRR_OX and species fluxes: The FDS user guide should be updated to explicitly state the relationship between HRR_OX and the species fluxes of O2 and the products of the solid phase oxidation reactions.
Perform a verification exercise: A verification exercise should be performed to ensure that the HRR_OX parameter is correctly implemented in the FDS model and that it is consistent with the surface fluxes in the gas phase.
Update the FDS test cases: The FDS test cases should be updated to include a verification case that specifically addresses the HRR_OX parameter.

Q: What is the future work for clarifying the relationship between HRR_OX and species fluxes?

A: The future work is to implement the recommendations above and ensure that the FDS model is correctly validated and verified. This will involve updating the FDS user guide, performing a verification exercise, and updating the FDS test cases.

Q: What are the references for further reading on the FDS model and the HRR_OX parameter?

A: The references are:

[1] McGrattan, K. B., Hostikka, S., & Floyd, J. E. (2013). Fire Dynamics Simulator (Version 6) User's Guide.
[2] McGrattan, K. B., Hostikka, S., & Floyd, J. E. (2013). Fire Dynamics Simulator (Version 6) Technical Reference Guide.