Transient Analyses and Energy Balance of Air Flow in Road Tunnels

Król, Aleksander; Król, Małgorzata

doi:10.3390/en11071759

Cited by 19 publications

(7 citation statements)

References 37 publications

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“…Another important conclusion is the need of carefully choosing of the turbulence model to be used. The k-ε and k-ω turbulence models, which are commonly regarded as industry standards [40][41][42][43][44], may fail when used for fire modeling in a confined space. This is due to expected anisotropy of flows, high velocity gradients and the essential role of buoyancy forces.…”

Section: Discussionmentioning

confidence: 99%

A Study on the Reliability of Modeling of Thermocouple Response and Sprinkler Activation during Compartment Fires

et al. 2022

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Real and numerical fire experiments involve temperature measurements with thermocouples, and thus some considerations on numerical modeling of this process are presented and a new approach to thermocouple modeling is introduced. Using ANSYS Fluent software a well-recognized analytical thermocouple model was implemented in each cell of the computational domain, which allows for determination of thermocouple responses as a continuous field. Similarly, sprinklers are key elements of fire-protection systems. Sprinklers activation is one of the breakthrough moments during the course of a compartment fire. Therefore, assumptions on sprinkler activation time are of crucial importance when designing a fire safety system. Just as for thermocouple modeling, virtual sprinklers based on a commonly admitted response time index (RTI) model were placed in all cells. The proposed approach provides data on sprinklers activation or thermocouple response for the whole domain instead of retrieving data point by point only for predefined locations. In this study, experimental data available in the literature were used for the validation of the proposed approach. In addition, the results were compared with those obtained with the commonly used Fire Dynamic Simulator (FDS) software. The outcomes might be of a significant importance for practitioners, who deal with fire experiments and fire protection. Furthermore, some issues on accurate modeling of fire gases flow are discussed extensively. It was found that commonly applied k-ε and k-ω turbulence models might fail in the case of modeling of fire plumes in confined spaces.

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Section: Discussionmentioning

confidence: 99%

A Study on the Reliability of Modeling of Thermocouple Response and Sprinkler Activation during Compartment Fires

et al. 2022

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“…Term k corresponds to the kinetic turbulence energy, ε is dissipation rate of turbulence energy and ω is specific dissipation rate of turbulence energy (ω = ε/k). Both of them are nowadays somewhat like industry standards, for instance Chen et al and Zhao et al used k-ε model [14,28], meanwhile Król and Król used k-ω model [29,30]. However using them one must be aware of their drawbacks and limitations.…”

Section: Selecting Of the Turbulence Modelmentioning

confidence: 99%

“…The latter approach assumes that from engineering point of view just averaged values are important. Thus the instantaneous fluid velocity (u) is regarded as a sum of the average velocity ( ) and fluctuating velocity (u′): [29,30]. However using them one must be aware of their drawbacks and limitations.…”

Section: Selecting Of the Turbulence Modelmentioning

confidence: 99%

Some Tips on Numerical Modeling of Airflow and Fires in Road Tunnels

Król

2021

Energies

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The efficiency of tunnels systems is often evaluated using numerical simulations. This concerns both to normal and emergency mode of tunnel systems operation. Therefore the safety level of tunnel users may depend on the quality of numerical models being built. The most often studied areas cover the researches on natural and forced airflows in the normal mode and on fire development and smoke spreading in the emergency mode as well as modeling of fan operation. Thus, many software packages implementing Computational Fluid Dynamics (CFD) are applied here. Despite the available software is recognized as reliable, the problem arises because the built numerical models should be validated at least partially with experimental data. There is a shortage of experimental data from real tunnels due to high costs and many organizational or formal difficulties. Some researchers use data from scaled experiments, but this leads to problems connected with scaling. The paper presents the application of two widely used software packages—Fire Dynamics Simulator (FDS) and ANSYS Fluent to reproduce some scenarios of the operation of a tunnel ventilation system for normal and emergency mode. Most of results were compared with data obtained by own full scale measurements or data available in literature. Some practical issues concerning the application of FDS and ANSYS Fluent were discussed as well.

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“…This solver has been widely used in fire research analyses and is recognized by some of the smoke control standards [26]. Some validation examples for ANSYS Fluent were given in [27][28][29][30][31]. The principal assumptions for numerical calculations and the choice of physical sub-models are summarized in Table 1.…”

Section: Case Study-numerical Modelmentioning

confidence: 99%

3D Mapping of the Sprinkler Activation Time

et al. 2020

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Sprinkler activation is one of the key events defining the course of a compartment fire. The time when activation occurs is commonly used in the determination of the design fire scenario, which is the cornerstone of the design of building fire safety features. A well-known model of sprinkler activation (response time index (RTI) model) was introduced into the numerical scheme of the ANSYS Fluent computational fluid dynamics (CFD) package. The novel way in which the model is used is the calculation of the time for sprinkler activation within each discrete cell of the domain. The proposed novel approach was used in a case-study to assess the effects of comfort mode natural ventilation on a sprinkler’s activation pattern. It was found that hinged vents in the comfort mode had a significant effect on sprinkler activation, both in terms of delaying it as well as limiting the total number of cells in which the sprinkler would have activated. In some scenarios with a hinged vent, no activation was observed in the central point of the vent, possibly indicating problems with the autonomous triggering of the fire mode of such a device. It was also found that the RTI and C (related to the conductive transport of sprinkler fitting) parameter values had a moderate influence on sprinkler activation time—only for high-temperature sprinklers (≥ 141 °C). This study shows the applicability of the 3D activation time mapping for research focused on the fire safety of sprinkler-protected compartments and for the performance-based approach to sprinkler system design. Even though the RTI model is the industry standard for the determination of sprinkler response, the model implementation in ANSYS Fluent was not validated. This means that sources of uncertainty, mainly connected with the determination of flow velocity and temperature are not known, and the model should be used with caution. An in-depth validation is planned for subsequent studies.

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Transient Analyses and Energy Balance of Air Flow in Road Tunnels

Cited by 19 publications

References 37 publications

A Study on the Reliability of Modeling of Thermocouple Response and Sprinkler Activation during Compartment Fires

A Study on the Reliability of Modeling of Thermocouple Response and Sprinkler Activation during Compartment Fires

Some Tips on Numerical Modeling of Airflow and Fires in Road Tunnels

3D Mapping of the Sprinkler Activation Time

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