Transverse Ventilation Research Articles

Experimental study on thermal and smoke control using transverse ventilation in a sloping urban traffic link tunnel fire

A set of full-scale experiments was conducted to study thermal and smoke control strategies using transverse ventilation system in a sloping urban traffic link tunnel (UTLT). Results showed that it is not the case that the slower the smoke spread longitudinally, the better the smoke being controlled. For transverse ventilation, within the smoke extraction compartment, the faster the smoke spread to the exhaust vents the faster the smoke being extracted from the tunnel. More importantly, the operation of the exhaust and supply vents for transverse ventilation in real time should take the effect of tunnel slope into consideration. For tunnel with a slope going uphill from upstream to downstream, supplying air from the downstream is recommended while supplying air from the upstream or directly to the fire located smoke compartment should be avoided. Additionally, for a given total smoke exhaust volume flow rate, increasing the number of exhaust vents is an effective way of controlling the smoke layer interface height. For the kind of tunnel as studied at hand, open the exhaust vents in the fire located compartment and its downstream smoke compartment is recommended.

횡류식 도로터널의 급배기구 개도율 최적화 프로그램 개발 연구

도심지 터널에 주로 적용되는 횡류식 환기방식은 환기구간 거리가 길어질수록 환기성능이 저하되므로 균일한 풍량분배가 필요하다. 본 연구에서는 환기구간 거리가 길어져도 균일한 풍량분배를 통해 설계값의 환기성능을 확보할 수 있도록 급배기구의 개도율을 최적화하는 프로그램을 개발하였으며, TUNVEN DUCT 프로그램과의 비교를 통해 프로그램의 예측 성능을 검증하였다. 이를 위해 반횡류 급기 환기방식을 적용하였으며, 두 프로그램은 유사한 포트 크기 및 풍량 분배를 예측하고 있으며, 계산값의 변동범위는 각각 11.71% 와 1.36% 인 것으로 나타났다. 이 프로그램은 다양한 터널 연장 및 급배기 포트 설치 조건에 대한 신속한 분석이 가능하므로, 횡류식 및 반횡류 환기방식의 포트 최적화 설계에 상당히 유용할 것으로 판단된다. The transverse ventilation system, commonly applied to urban tunnel, is necessary to be distributed with airflow uniformly. In this study, we developed a program that can optimize the opening ratio of ports to ensure ventilation performance of design criteria through a uniform airflow distribution even though ventilation interval becomes longer. And program's prediction performance was verified by comparison with TUNVEN DUCT program. For comparison, Semi-transverse ventilation system was applied. Both programs predicted a similar port size and air flow distribution, and the variation range of the calculated values was 11.71% and 1.36%, respectively. This program is very useful for port optimization design of transverse and semi-transverse ventilation system, because it is possible to analyze various tunnel lengths and supply/exhaust port installation conditions.

Numerical studies on the smoke control by water mist screens with transverse ventilation in tunnel fires

Emergency ventilation systems are commonly used for smoke control during tunnel fires. For the transverse ventilation system, high efficiency for fire safety could be obtained by confining the smoke within certain zones. In this paper, a new system with simultaneous water mist screen and transverse ventilation system (WMSTV system) is proposed. In the WMSTV system, water mist screens are used to confine smoke from spreading widely, which assists the smoke exhausting process of the transverse ventilation system. Numerical method is used for investigation in this paper. The effects of natural and transverse ventilation systems without water mist are also investigated for comparison. Numerical results show that the WMSTV system can confine the fire and smoke effectively and the environment inside the confined zone would be suitable for occupants evacuation and firefighting. The system can be regarded as a feasible strategy for smoke control in tunnels.

A Fundamental Study for Optimizing the Supply and Exhaust Port Opening Ratio in Road Tunnels with Transverse Ventilation System

A Fundamental Study for Optimizing the Supply and Exhaust Port Opening Ratio in Road Tunnels with Transverse Ventilation System

Performance evaluation of longitudinal and transverse ventilation for thermal and smoke control in a looped urban traffic link tunnel

The complex structure of the urban traffic link tunnel (UTLT) exacerbates fire accident risk and increases the difficulty of smoke control, especially for a UTLT with looped tunnel systems. The applicability of the traditional tunnel smoke control methods, e.g., transverse ventilation and longitudinal ventilation, needs further investigation for UTLTs. Experiments were conducted in a small-scale model to investigate the effectiveness of both two ventilation modes for a looped UTLT. In a longitudinally ventilated UTLT, the critical velocities, as the minimal air velocities for preventing smoke infiltrating into the regions upstream of the fire and entering the downstream tunnel branches that are adjacent to the smoke discharge route, should be guaranteed. Multiple operational modes of longitudinal ventilation could be feasible for achieving the desired performance of smoke control. For transverse ventilation, both the effects of the exhaust flow rate and the air supply rate are investigated. To confine the smoke in the tunnel branch where fire occurs, an effective exhaust flow rate could be twice the smoke production rate. Forced air supply could be unnecessary for a UTLT due to the abundance of natural air supply routes. Longitudinal ventilation leads to lower smoke flow temperatures than transverse ventilation does in UTLTs.

Effect of Transverse Aspect Ratio and Distinct Ventilation Techniques on Convective Heat Transfer from a Rectangular Enclosure: Experimental and Numerical Study

Our objective in this study was to investigate the convective heat transfer in a cavity with ventilation ports. The study has been divided into experimental and numerical sections and under the experimental study the enclosure considered with two exit ports at roof and one inlet opening with varying aspect ratio. Under the numerical study, the model validation is done at AR = 5, and then the study continued for one exit port each on the left side and right side. The enclosure is equipped with three discrete heat sources at the bottom wall and with an exhaust fan at the exit port. The ranges of parameters considered under experimental study as 1.25 ≤ AR ≤ 2.5, 3224 ≤ Re ≤ 6579, 8.5 × 106 ≤ Gr ≤ 1.03 × 108, and as a consequence Richardson number obtained in the range 0.21–9.58. Experimental results set out that the heat source surface Nusselt number decreases with an increase in aspect ratio however; at higher aspect ratio, the values of Nusselt number remain almost unchanged. The enclosure bulk fluid Nusselt number increases with an increase in aspect ratio. The study revealed that for a given aspect ratio with an increase in Re, the heat source Nu increases. The numerical study divulged that the ventilation port arrangement at the right side of enclosure exhibits the better thermal performance among all the three orientations considered and the results are supported with the streamline and temperature contours. The study of varying inlet port height disclosed that as the inlet port height is increased, the heater surface temperature drops and the enhanced heat transfer is achieved.

대심도 터널 화재 시 균일배기 환기방식에서의 최적배연 연구

This study represents the effective fire and smoke control in the case of fire in deep underground tunnels, even if the exhaust system can be calculated, the optimal smoke capacity can be determined by establishing technical standards for the transverse ventilation system focusing on the design as a basis for deriving the parameters for utilization. Numerical analyses were performed using the FDS program as a function of the unsteady flow in a deep underground tunnel fire. The analysis results were calculated within 250 m smoke using an inside wind velocity of 0m/s when the capacity of smoke was exhausted, 80 m 3 /s, whereas in case of an internal wind velocity of 3m/s, the

Performance validation of a hybrid ventilation strategy comprising longitudinal and point ventilation by a fire experiment using a model-scale tunnel

We examined the exhaust performance of a hybrid ventilation strategy for maintaining a safe evacuation environment for tunnel users in a tunnel fire. The hybrid ventilation strategy combines the longitudinal ventilation strategy with the point ventilation strategy which is a type of transverse ventilation strategy. The model tunnel developed by this study was scaled to 1/5 the size of a full-scale tunnel. The model-scale experiment was performed taking into consideration Froude's law of similarity. Measurement items were the distribution of temperature and concentration of smoke inside the tunnel, longitudinal wind velocity, mass flow of smoke in the point ventilation duct, and the heat release rate of the fire source. The following main conclusions were obtained. The smoke height was constant even when varying the extraction rate of smoke from the ceiling vent. The backlayering length and critical velocity of the smoke flow in the hybrid strategy could be predicted by the methodology developed by using the longitudinal strategy. The hybrid strategy maintained a safe evacuation environment on both sides of the tunnel fire.

Analysis of Influencing Factors on Flashover in the Long-narrow Confined Space

The traditional theory of flashover is not available for the application of flashover in a long-narrow confined space, especially about the critical condition of flashover occurrence. In this paper, according to the measurement of reduced-scale fire tests, the smoke layer's temperature, thickness, gas concentration and heat release rate of fire source were studied. Furthermore, the effects of fire source, opening and ventilation to the occurrence of flashover were further discussed. It is shown that the critical line of flashover for the different fuels is between 600°C and 700°C, and critical condition is different for different fuels and different openings; for the different transverse ventilation, the smoke evacuation has the best effect only when the exhaust port neat the fire is opened.

내화패널이 부착된 프리캐스트 PSC 풍도슬래브의 정적/동적하중에 관한 실험연구

In the longway tunnel and underground traffic road, the structure of transverse ventilation system is constructed by the airpit slab. In this study, the full scale specimens of the PSC airpit slab that attached fire resistance panel are performed the static and dynamic loading tests for evaluation of bending capacity. The first of all, it confirmed the evaluations about the fundamental efficiency of the fire resistance panel and PSC slab by the 3-point bending test and pull-off test. The tests are performed for evaluation of the bending resistance under ultimate static load and the bonded capacity under dynamic fatigue load. A fatigue test is performed for an investigation of the effect on wind pressure that is developed by transit of traffic. The damage or debonding on surface between fire resistance panel and PSC slab was not developed in dynamic fatigue load test, also the behavior of the specimens is very stable and the debonding of the fire resistance panel attached at the bottom surface of PSC slab was not developed in static load test, too. Therefore, the crack or debonding of the fire resistance panel will be not developed by external loads during the construction or completion of the precast fire resistance system.

Slope flows governed by diffusion effects in seas, lakes, and reservoirs

The hydrodynamics of slope flows governed by heat and salt diffusion near a rigid sloping impermeable boundary in stratified water bodies is studied. The physics of this phenomenon consists in that, because of the impermeability of the shore slope, the fluxes of heat and salt normal to the slope surface must be zero. Since the background stratification does not meet this condition, diffusion boundary layers appear along the shore slope. It is shown that, depending on the ratio between diffusion coefficients of heat and salt and the parameters of stratification by temperature and salinity, of convection the slope flows can be either ascending or descending. Moreover, under some conditions, a finger-type regime can form in boundary layers, though the background stratification is stable. The appearing slope flows, though they are local, initiate global transverse ventilation of water in the entire water body.

Upgrade of a transverse ventilation system in a bi-directional tunnel

The Karavanke tunnel forms an important link between Slovenia and Austria. The almost 8 km long tunnel is operated with bi-directional traffic and does not have dedicated escape routes. Moreover, the ventilation in case of fire does not satisfy requirements of the EU Directive 2004/54/EC that specifies the minimum requirements for tunnels in the trans-European road network. The paper present results of the research conducted regarding the possibility of upgrade the existing system in order to reach the required level of safety at lower costs possible. It is shown that with simple but novel adaptations of the ventilation system, a sizeable increase in the overall level of safety can be achieved. The methodology applied is a combination of a simple pipe model for tunnel ventilation and for detailed fluid dynamics analysis the CFD model is used. The existing ventilation system that in fire ventilation extracts smoke from a single duct is replaced with the smoke extraction from both ducts applying four axial fans. The analysis is focused on air/smoke flow through the vents and ducts and on pressure drops calculated over the length of the ventilation duct and its influence on the total flow. The change of the flow condition also has influence on ventilation fan operation point that is investigated in the paper as well.

A study on long tunnel smoke extraction strategies by numerical simulation

The performance of different smoke extraction strategies for a long vehicle tunnel was investigated for a 100 MW fire scenario. Computer modeling was used for the investigation with a numerical simulation method. The selection of single-point extraction (SPE) opening strategy versus multi-point extraction (MPE) opening strategy was analyzed. In the single-point extraction (SPE) opening strategy, the smoke spread was found to be contained between the fire site and the point of smoke extraction. This result was obtained when the tunnel air velocity reached the critical velocity for preventing back-layering of smoke. For multi-point extraction (MPE) strategies with more than one opening, the smoke spread to all the extraction openings. Moreover for MPE strategy, air velocities were found to be slower near the middle openings and could be less than the critical velocity. Distributions of smoke spread, CO, visibility and temperature were analyzed. It was found that visibility of smoke and temperature were the key factors for safe evacuation of the personnel in tunnel. The SPE system was found to be more effective than the MPE system for partial transverse ventilation systems.

Experimental simulations of fire-induced smoke control in tunnels using an “air–helium reduced scale model”: Principle, limitations, results and future

When a fire occurs in a long tunnel, smoke control is crucial for obvious reasons of safety. Ventilation and extraction systems have to be designed with accuracy in order to control the longitudinal motion of the fire-induced smoke and to extract it efficiently in a zone close to the fire source. This paper presents experimental investigations carried out on a small scale tunnel model (scale reduction is 1:20) to study the fire-induced smoke control by longitudinal and transverse ventilation systems. The experimental model is non-thermal and a buoyant release (a mixing of air and helium) is used to represent the fire smoke plume. The main objective of this model is to represent, as well as make possible, the duality between inertial forces (due to ventilation) and buoyant forces. Radiation and heat losses at the walls are not taken into account in this model. At first, the principle of the simulation is widely described. Then, some results are presented for both longitudinal and transverse smoke control by a mechanical ventilation. Finally, perspectives for future investigations are proposed.

Application of CFD Method for Risk Assessment In Road Tunnels

The definition of the deterministic approach in safety analyses arises from the need to understand the conditions that emerge during a fire accident in a road tunnel. The key factor of the tunnel operations during a fire is ventilation, which during the initial phases of the fire has a strong impact on the evacuation of people and later on the access of the intervention units to the tunnel. The paper presents the use of the CFD (Computational Fluid Dynamics) model in tunnel safety assessment process. The set-up of the initial and boundary conditions and the requirement for grid density found from validation tests of an FDS (Fire Dynamics Simulator) are used to prepare three kinds of fire scenarios—20 MW, 50 MW and 100 MW, with different ventilation conditions: natural, semi-transverse, transverse and longitudinal ventilation. The observed variables, soot density and temperature, are presented in minutes time steps through the entire tunnel length. Comparing the obtained data in a table allows the analyses of the ventilation conditions for different heat releases from fires. The second step is to add additional criteria of human behaviour inside the tunnel (evacuation) and human endurance to the elevated gas concentrations and temperature. What comes out is a fully deterministic risk matrix that is based on the calculated data where the risk is ranged on five levels, from the least to a very dangerous level. The deterministic risk matrix represents the alternative to a probabilistic safety assessment methodology, wherein the fire risk is represented in detail and the CFD model results are physically correct.

Methodology of using CFD-based risk assessment in road tunnels

The definition of the deterministic approach in the safety analyses comes from the need to understand the conditions that come out during the fire accident in a road tunnel. The key factor of the tunnel operations during the fire is the ventilation, which during the initial fazes of the fire, impact strongly on the evacuation of people and latter on the access of the intervention units in the tunnel. The paper presents the use of the computational fluid dynamics model in the tunnel safety assessment process. The model is validated by comparing data with experimental and quantifying the differences. The set-up of the initial and boundary conditions and the requirement for grid density found during the validation tests is used to prepare three kind of fire scenarios 20 MW, 50 MW, and 100 MW, with different ventilation conditions; natural, semi transverse, full transverse, and longitudinal ventilation. The observed variables, soot density and temperature, are presented in minutes time steps trough the entire tunnel length. Comparing the obtained data in a table, allows the analyses of the ventilation conditions for different heat releases from fires. The second step is to add additional criteria of human behaviour inside the tunnel (evacuation) and human resistance to the elevated gas concentrations and temperature. What comes out is a fully deterministic risk matrix that is based on the calculated data where the risk is ranged on five levels, from the lowest to a very danger level. The deterministic risk matrix represents the alternative to a probabilistic safety assessment methodology, where the fire risk is represented in detail as well as the computational fluid dynamics model results are physically correct. .

A study on the carbonation of the lining of vehicular tunnel based on ventilation system

This study was performed to analyze the carbonation of the tunnel linings concentrating on the 7 public service-in road tunnels in Korea and to commpare the trend of carbonation as to ventilation systems. The progress of carbonation in study was more conspicuous at the end of tunnels than the beginning of it. Likewise, it was remarkable in the tunnels of semi-transverse ventilation and transverse ventilation system rather than natural ventilation system, because traffic and other contaminants are more in such ventilation systems. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.

Experimental Investigation on Smoke Propagation in a Transversely Ventilated Tunnel

In order to determine the key features of the fire safety design in transversely ventilated tunnels, the smoke propagation characteristics are examined as a function of fire size, fire location, and airflow rates of supply and exhaust. A 12-m long scale model of the Memorial tunnel, with a scale down ratio of cross section 1/20, is used. Fire sizes and ventilation rates in real tunnels are then deduced from the Froude similarity. In general, it is found that the smoke propagating distance increases with the fire size and decreases with the exhaust ventilation rate. When the fire location is off-centered, the propagating distance becomes substantially larger than that of the centered fire with the same size. A hazardous situation generated from an imbalance between the supply rate and the exhaust rate is also observed. The results suggest that the smoke propagating distance and/or the smoke filling may serve as good criteria for determining the transverse ventilation rate.

The design of tunnel ventilation system for a long vehicular tunnel

Longitudinal, semi-transverse and transverse ventilation systems are the traditional approaches employed in the design of vehicular tunnel ventilation system. The Memorial Tunnel Fire Ventilation Test Program which carried out full-scale tests on fire heat release rate up to 100 MW for various ventilation schemes had demonstrated that longitudinal tunnel ventilation system is an effective means of controlling smoke during fire emergency. Consequently, many of the short vehicular tunnels have been designed with longitudinal tunnel ventilation system using a series of jet fans to bring pollutants out of the portal and to create an air velocity greater than critical velocity to prevent the backlayering of smoke during fire. However, the major constraints of longitudinal ventilation system are the excessive air volume and air velocity, and that it cannot ventilate long uni-directional vehicular tunnel due to the building up of pollutant concentration levels in the direction of travel unless air exchange points are provided. Long vehicular tunnel coupled with long slip roads presents special challenges in tunnel ventilation system design. During normal traffic operation, the vehicular emissions have to be removed to ensure that the air quality in the tunnel is kept within acceptable limits. The pollutants discharged from the ventilation buildings to the atmosphere have an air quality impact on surrounding development which has to be carefully assessed. The ventilation system also has to be designed to prevent the building up of temperature beyond tolerable limit during traffic congestion where vehicles may pile up bumper to bumper for several kilometres. When there is a fire emergency, smoke control to enable safe evacuation has to be addressed for the main tunnel, long in-ramps and long out-ramps. This paper describes the design of the ventilation system for the Kallang/Paya Lebar Expressway which is a major expressway in Singapore linking the East Coast Parkway in the south and the Tampines Expressway in the north. It is a complex project made up of tunnels, slip roads, viaducts, open expressways and ventilation buildings. It has a total length of 12 km of which approximately 8.7 km is in tunnel. The Expressway tunnel is linked to 8 entry and 9 exit slip roads and will be one of the longest dual three-lane road tunnels in Southeast Asia when completed in 2007. This paper addresses the major elements in the design of the tunnel ventilation system for the Expressway tunnel including: (a) Evaluation of different types of ventilation systems. (b) Air quality impact on the environment. (c) Ventilation system design for normal and congested traffic operation. (d) Ventilation system design for fire emergency operation. (e) Special considerations for long in-ramps and long out-ramps. Subway Environmental Simulation program has been used in the analysis of the ventilation system. As some the concepts employed in the design are unique, Computational Fluid Dynamics (CFD) techniques have been employed to validate the design. The results of the CFD analysis are presented in this paper. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

横流換気トンネルにおける圧力分布特性の実験的検証(トンネル換気)

The aim of this investigation is to evaluate of transverse ventilation system for road tunnels. Developed tunnel simulator had a main duct and 390 air-nozzles for air supply and exhaust. In order to control flow rate of the main duct, the small nozzles were consisting of brass tubes and stainless steels with small orifice. The pressure distribution of the main tunnel can be evaluated by using this simulator. Measured pressure distributions of longitudinal and full transverse ventilation were good agreement with predicted value obtained from the momentum theory. However, in the case of semi-transverse ventilation, the experimental results differ from the theoretical one. In order to modify the accuracy of prediction, the current equation requires some revision by experiment data. Various transverse ventilation systems are available under the present experimental system.