Road Tunnel Ventilation Research Articles

Tunnel Ventilation Silencer Replacement Project

Silencers play a major role on road and rail tunnel ventilation projects throughout North America and the globe. They are instrumental in acheving the required dBA levels; specifically for emergency announcements. Vibro-Acoustics was called to replace silencers that began rusting internally. This caused metal pieces to break off during fan operation. Blade strikes were discovered by maintenance personel which promped an entire replacement task. This was a challenge in itself to remove the existing silencers and install new ones in their place as many space restrictions were present. The new silencers had to be fabricated in a way to meet the stringent acoustic requirements but also for ease of installation. They consisted of 84" inlet and 144" discharge lengths to acheive the noise requirements both at the track level and nearly street level. The silencers consisted of 3/16" plate casings and G235 18 gauge baffles as per the engineers specification. This presentation will show the steps taken to remove the old silencers, the challenges of installing the new silencers, and the testing process for ceritfiying the acoustic performance by a third party acoustical consulant located in NYC. Vibro-Acoustics was involved throughout the entire project which dates back to 2018.

Impact of Dual Fire Sources on Temperature Distribution and Smoke Ventilation in Road Tunnels with Shafts

Impact of Dual Fire Sources on Temperature Distribution and Smoke Ventilation in Road Tunnels with Shafts

Experimental study on the performance of synergistic ventilation system combining shaft with mechanical ventilation in extra-long road tunnels

Ventilation shafts are widely equipped in extra-long road tunnels. Due to the plug-holing phenomenon, it may be impossible to improve smoke extraction performance solely by increasing extraction velocity in a traditional ventilation shaft. Taking reference from practices in mine ventilation shafts, a novel mechanical board-coupled ventilation shaft (MBCS) was introduced. A total of 120 experiments in a 1:20 reduced-scale tunnel model were conducted to validate the effectiveness of the novel shaft. The effects of shaft height, board location, and extraction velocity were investigated, and the interaction dynamic mechanism of synergistic smoke extraction between fan-driven and shaft-driven was revealed. The results indicate that the novel MBCS can achieve better smoke extraction performance as the extraction velocity increases. Besides, compared to the traditional MBCS in our previous study, the smoke extraction efficiency of the novel MBCS improves by 19.8 %, the heat extraction performance improves by 75.7 %. Moreover, based on theoretical and dimensional analysis, a model to analyze the dynamic mechanism of synergistic smoke extraction was established, which may provide positive insights for smoke control and extraction design both in extra-long road tunnels and mine ventilation shafts.

Numerical Simulation of Airflow Distribution in the Tunnel of Cairo Metro Line 3 Using CFD

One of the problems facing the underground tunnels is lacking enough fresh air for passengers inside the subway. Also, because of the friction of the train with the railways, high heat is generated. So, the use of computational fluid dynamics to distribute the required fresh air flow at the lowest possible cost is critical for the tunnels. In this research, Computational Fluid Dynamics (CFD) is used to perform 3D modelling and simulation for the tunnel of Cairo Metro Line No. 3. The standard k-e turbulence model was used in the CFD analysis to simulate the ventilation airflow in a 1075m tunnel length. The simulation reveals that the tunnel airflow rate induced by the speed of the fan is more desirable. Also, the addition of a jet fan causes an eddy current that improving the efficiency of tunnel ventilation, thereby greatly reducing ventilation time, and increasing efficiency in cases where the diameter of the tunnel equals 15 m, the speed of the fan is 1480 r.p.m, and the air flow rate is 80- 120 m3/s. This led to improve fan speed efficiency and airflow distribution in the tunnel. Similar way of simulation is used for road tunnel ventilation.

Incorporation of Green Infrastructure on Road Tunnel Ventilation Stacks: Potential Ambient Air Quality Improvement

Vehicular tunnels are an important part of transportation infrastructure, though there are concerns about air quality due to the concentrated release of polluted air at roadway portals and tunnel ventilation stacks. Urban green infrastructure offers opportunities as a nature-based solution to mitigate urban particulate matter pollution. Green walls have advantages over other types of urban green infrastructure, since they can be potentially applied to large vertical surfaces available within cities and since they can be retrofitted onto already built structures. However, uptake of green wall technology has been limited on infrastructure projects, let alone the integration of green walls and roadway portals and tunnel ventilation stacks, which represents the first of its type worldwide. Therefore, this study aims to describe the integration of green wall technologies and a tunnel ventilation facility, and models the potential ambient air quality improvement the green wall plants have through PM2.5 dry deposition. It was found that the project would increase ambient PM2.5 to a concentration of 13.6 ug/m3, and that the green walls would have the capacity to remove significant amounts of PM2.5, from not only the ambient air pollutant increase as a result of the ventilation outlets, but also the background and surrounding surface road contributions. Differences in the rate of pollutant removed per stack by the green walls were attributed mostly to the varying ratios of plants installed. The findings indicate the air quality benefits of green wall integration on major infrastructure projects, which will assist in the overall sustainability appraisal of large infrastructure projects which need to balance the needs of population growth with environmental and human health.

The results of physical modeling of fires for road tunnels

The paper gives the results of a fire development study using physical models of inclined vehicular traffic tunnels scaled 1:60. The tunnel inclination varied within 0-10% with a 2% increment. The fire strength initiated and developed in a natural tunnel varied within 5-15 MW with a 5 MW increment. The length of the natural tunnel was 360 m, width: 8 m, height: 6 m, cross-sectional area: 48 m2, and the tunnel width and height ratio: 1.33. The model of the natural tunnel of the given geometry was made of a 2-mm-thick stainless steel sheet with an appropriate scale. The sizes of the tunnel model are: length: 6 m, width: 0.16 m, height: 0.12 m, and cross-sectional area: 0.0192 m2. By doing experiments on this model, we studied the nature of propagation of gases (smoke) emitted during the fire initiation and development, specified the impact of the gradient factor on the rate of variability of the critical velocity and backlayering distance. The said characteristics were studied according to the air temperature variability in the tunnel model. The air temperature was measured with K-type thermocouples equipped with open and closed detectors. Maximum measuring temperature was 800°C. The thermocouples were installed in the ceiling of the tunnel model along the entire length, with 5 and 10 cm increments. The fire was modeled with natural gas. Ventilation air was supplied into the model by an axial fan from one portal of the model. The velocity of the ventilation air was measured with an anemometer, and the air discharge was calculated at every moment according to the velocity. The required strength of the modeled fire was provided by natural gas, and the measurement was done with a volumetric and mass regulatory meter. Simultaneous data collection, processing, analysis and digital transmission of data from the K-type thermocouples, anemometers and natural gas flow meters were provided with DT-85 Datataker. The obtained results can be used to develop road tunnel ventilation projects that take into account the impact of fires on ventilation.

Field measurements of vehicle pollutant emissions in road tunnels at different altitudes

Many previous studies have focused on air quality in road tunnels, which is a major concern for ventilation design. However, few researchers have investigated the air quality in tunnels in high-altitude areas. The ambient environment in high-altitude areas featuring low oxygen content and ambient pressure can influence the vehicle pollutant emissions inside the tunnels. As a result, field measurements were carried out considering environmental parameters and gaseous pollutant concentrations in four road tunnels at different altitudes to determine exact vehicle emissions. Results show that ambient pressure is closely related to the altitude and that the oxygen content will decrease when the altitude increases due to the lower air density. The air velocity induced by the vehicle fleet is only affected by the traffic parameters and not influenced by the air density. The CO and NO emission factors in test tunnels at different altitudes were calculated according to pollutant mass balance models. We can conclude that an environment featuring low oxygen content and ambient pressure in high-altitude areas contributes to incomplete combustion of the engines and performance degradation of the catalytic converter, which leads to higher toxic pollutant emissions inside the tunnels. In this study, the CO and NO emission factors were 0.701 and 0.403 g km−1 vehicle-1 respectively at an altitude of 500 m, which then increased to 1.567 and 0.886 g km−1 vehicle-1, respectively, at an altitude of 3850 m. The NO altitude coefficient is introduced, similar to the CO altitude coefficient in the guidelines, to reflect the influence of altitude on the NO emission factor, and we can determine that the impact of altitude on the CO emission factor is greater. We hope our work will provide a reference for road tunnel ventilation design in high-altitude areas.

An integrated approach for the analysis and modeling of road tunnel ventilation. Part II: Numerical model and its calibration

The present work represents the second and final part of a twofold study aiming at the definition and validation of an integrated methodology for the analysis and modeling of road tunnel ventilation systems. A numerical approach is presented, based on the Finite Volume integration of the 1D mechanical and thermal energy conservation equations on a network of ducts, representing the ventilation system of the 11.6 km long Mont Blanc Tunnel. The set of distributed and concentrated loss coefficients, representing dissipation of mechanical energy by friction in each part of the ventilation system, is calibrated against a rich experimental dataset, collected throughout a dedicated set of in situ tests and presented in the first part of the work. The calibration of the model is carried out by means of genetic optimization algorithms. Predictions of the flow field using the calibrated parameters are in remarkable agreement with the experimental data, with an overall RMS error of ± 0.27 m/s, i.e. of the same order of the accuracy of the measurement probes. Further validation against a selection of field data recorded by the tunnel monitoring and control system is brought forward, highlighting the robustness and potential general applicability of the proposed approach.

An integrated approach for the analysis and modeling of road tunnel ventilation. Part I: Continuous measurement of the longitudinal airflow profile

The knowledge of the flow field inside road tunnels under normal operation, let alone fire conditions, is only approximate and partial. The reason is that while the full three-dimensional, unsteady problem is out of reach of numerical methods, on the other hand accurate measurement of the airflow in road and railway tunnels constitutes an extremely demanding task. The present work, structured as a twofold study, takes up the challenge and proposes an original integrated experimental and numerical approach for the analysis and modeling of flow inside a road tunnel and its ventilation systems, aiming at defining a methodology for the creation of “digital twins” of the system itself, on which advanced ventilation and smoke control strategies can be tested and fine-tuned. In this first part, an innovative experimental facility for the continuous acquisition of the longitudinal velocity profile along the whole length of a road tunnel has been designed and built. The facility consists of a survey rake with five bidirectional vane anemometers, which is mounted on a small electric vehicle that can travel through the tunnel at constant speed. This paper reports the design procedure of the measurement facility, with particular focus on the conception and realization of the vehicle carrying the survey rake. Results of the first experimental campaign carried out under the 11611 meters long Mont Blanc road tunnel are presented to corroborate the validity of the approach adopted and the accuracy of the measurement chain.

Analysis of calculation of fresh-air demand for road tunnel ventilation design in China

At present, road tunnel ventilation system design in China is calculated with reference to the 2014 China Guidelines. However, with the continuous renewal of vehicle and more stringent emission laws, calculation results based on parameters in the 2014 China Guidelines are significantly different from the actual situation, which will cause a great waste of ventilation system. According to investigating the domestic and foreign tunnel ventilation design standards, a calculation example was used to analysis the impact of emission generation formula, base emission rates and time factors on ventilation system design. The results show that 2017 Shanghai Code and 2019 PIARC Ventilation Report consider the impact of NO2 and non-emission particles on fresh-air demand in tunnel, while 2014 China Guidelines do not. For base emission rates, three standards take 2000, 2010 and 2018 respectively as the base years. The 2014 China Guidelines provides the base emission rates in a fixed value, while the other two criteria provide more precise values. For time factor, three standards stipulate the annual average attenuation is 2%, 6% and 5% respectively. Compared with 2014 China Guidelines, the required fresh-air flow rate of an example tunnel calculated by the 2017 Shanghai Code and 2019 PIARC Ventilation Report was reduced by 24.5% and 21.7% respectively. The research results clarify the similarities and differences between three road tunnel ventilation design standards, and quantitatively present the gaps in calculation of fresh-air demand caused by different factors, which provide a reference for the ventilation design of tunnel in China.

Risk-based life cycle cost analysis using a two-level multi-objective genetic algorithm

ABSTRACT The aim of this study has been to develop a two-level multi-objective genetic algorithm (MOGA) to optimize risk-based LCC analysis to find the optimal maintenance replacement time for road tunnel ventilation fans. Level 1 uses a MOGA based on a financial risk model to provide different risk percentages, while level 2 uses a MOGA based on an LCC model to estimate the optimal fan replacement time. Our method is compared with the approach of using a risk-based LCC model. The results are promising, showing that the risk-based LCC offers the possibility of significantly reducing the maintenance costs of the ventilation system by optimising the replacement schedule by considering the risk costs. The risk-based LCC can be used with repairable components, making it applicable, useful and implementable within Swedish Transport Administration (Trafikverket). In this study, MOGA operators have selected the cost of maintenance and risk data through the previous levels using different ways to provide different possible solutions. A drawback of the MOGA based on a risk-based LCC model with regard to its estimation is that a late replacement period over 20-year period might increase the maintenance cost. Therefore, the MOGA does not provide a good solution for a risk-based LCC.

Road Tunnel Axial Fan Performance In Situ Test: Taking Qinling Zhongnan Mountain Highway Tunnel as an Example

Axial fans play a pivotal role in the road tunnel ventilation system. Qualified performance of the axial fan is important for both safety and air quality maintenance reasons. Axial fans performance in situ test of Qinling Zhongnan Mountain highway tunnel, the second longest road tunnel in the world, is presented in this research. Performance test items and the qualification criterion, as well as a general framework for the road tunnel axial fan assessment, are recommended. Log-Tchebycheff method is suggested to confirm the location for the measuring lines and points. The precision of the log-Tchebycheff method in air flow rate measuring is verified by comparing with the biharmonic spline interpolation fitting result. The research shows that the log-Tchebycheff method has high precision and good efficiency in the air flow rate measurement of the road tunnel air duct. What is more, the biharmonic spline interpolation fitting method can be applied to obtain a more accurate result. The number of interpolation points of the biharmonic spline interpolation fitting method should be bigger than 2000 to provide quality results.

Change the road tunnel ventilation equipment and its system consideration

Change the road tunnel ventilation equipment and its system consideration

Optical density of testing aerosol and fire smoke in a road tunnel with longitudinal ventilation: comparison by FDS6

Specific testing aerosol is used for road tunnel ventilation tests to represent steady-state movement of fire smoke downstream of the fire and to avoid the damage of the tunnel. This study investigates the spread of aerosol in 240 m long section of a road tunnel by computer simulation using the well-known FDS simulation system and compares it with the fire smoke spread. Conditions under which optical density for both cases is similar are determined, mainly the mass flux of aerosol needed to represent the smoke produced by fire and the distance at which steady-state flow of smoke is formed. The influence of the fire HRR and air flow velocity on the determined aerosol mass flux is studied as well. The determined value of mass flux increases with increasing flow velocity and decreases with increasing fire HRR. The results indicate that the aerosol can be used to represent the optical density of steady-state fire smoke spread downstream of the fire in tunnel ventilation tests.

Natural Ventilation of a Small-Scale Road Tunnel by Wind Catchers: A CFD Simulation Study

Providing efficient ventilation in road tunnels is essential to prevent severe air pollution exposure for both drivers and pedestrians in such enclosed spaces with heavy vehicle emissions. Longitudinal ventilation methods like commercial jet fans have been widely applied and confirmed to be effective for introducing external fresh air into road tunnels that are shorter than 3 km. However, operating tunnel jet fans is energy consuming. Therefore, for small-scale (~100 m–1 km) road tunnels, mechanical ventilation methods might be highly energetically expensive and unaffordable. Many studies have found that the use of wind catchers could improve buildings’ natural ventilation, but their effect on improving natural ventilation in small-scale road tunnels has, hitherto, rarely been studied. This paper, therefore, aims to quantify the influence of style and arrangement of one-sided flat-roof wind catchers on ventilation performance in a road tunnel. The concept of intake fraction (IF) is applied for ventilation and pollutant exposure assessment in the overall tunnel and for pedestrian regions. Computational fluid dynamics (CFD) methodology with a standard k-epsilon turbulence model is used to perform a three-dimensional (3D) turbulent flow simulation, and CFD results have been validated by wind-tunnel experiments for building cross ventilation. Results show that the introduction of wind catchers would significantly enhance wind speed at pedestrian level, but a negative velocity reduction effect and a near-catcher recirculation zone can also be found. A special downstream vortex extending along the downstream tunnel is found, helping remove the accumulated pollutants away from the low-level pedestrian sides. Both wind catcher style and arrangement would significantly influence the ventilation performance in the tunnel. Compared to long-catcher designs, short-catchers would be more effective for providing fresh air to pedestrian sides due to a weaker upstream velocity reduction effect and smaller near-catcher recirculation zone. In long-catcher cases, IF increases to 1.13 ppm when the wind catcher is positioned 240 m away from the tunnel entrance, which is almost twice that in short-catcher cases. For the effects of catcher arrangements, single, short-catcher, span-wise, shifting would not help dilute pollutants effectively. Generally, a design involving a double short-catcher in a parallel arrangement is the most recommended, with the smallest IF, i.e., 61% of that in the tunnel without wind catchers (0.36 ppm).

Analysis on ventilation pressure of fire area in longitudinal ventilation of underground tunnel

In order to solve the problem of ventilation pressure loss in the fire area under the fire condition, the wind pressure loss model of the fire area is established based on the thermodynamic equilibrium relation. The semi-empirical calculation formula is obtained by using the model experiment and CFD simulation. The validity of the formula is verified. The results show that the ventilation pressure loss in the fire zone is proportional to the convective heat release rate at the critical velocity, which is inversely proportional to the upstream ventilation velocity and the tunnel cross-sectional area. The proposed formula is consistent with the law of the tunnel fire test fitting formula that results are close, in contrast, the advantage lies in a clear theoretical basis and ventilation velocity values. The resistance of road tunnel ventilation system is calculated accurately and reliably, and then an effective emergency ventilation operation program is developed. It is necessary to consider the fire zone ventilation pressure loss. The proposed ventilation pressure loss formula can be used for design calculation after thorough verification.

Optimization-based control of ventilation in a road tunnel complex

This paper introduces a novel approach for controlling the operational ventilation in complex road tunnels. Basically, the control structure is feed-forward with an adaptive logic. The feed-forward part includes the static optimization which uses the mathematical model of airflow dynamics. The adaptive logic is based on the recursive least squares with exponential forgetting, which compensates deviations between the mathematical model and real measured data, and thus provides a feedback. During the standard operation of road tunnels, requirements to maintain indoor air quality (IAQ) and protect the surrounding area of a tunnel from pollution, are necessary. Moreover, reducing electricity costs is desirable, as the ventilation in road tunnels forms a significant part of electricity costs. The control scheme has been validated through the long-term evaluation of operation in the Blanka tunnel complex in Prague, Czech Republic, which is the largest city tunnel in Central Europe. The experimental validation of the proposed control scheme is the main contribution of the paper.

Natural ventilation of urban shallowly-buried road tunnels with roof openings

China has constructed a number of urban shallowly-buried road tunnels with roof openings, and their air quality has attracted favourable comments. However, no satisfactory theoretical model has been constructed for this type of tunnel and experimental data is lacking. Moreover, its design conflicts with existing building codes. It has been assumed that the pressure fluctuation produced by vehicle motion causes a respiratory phenomenon at the roof opening, with alternating inward and outward air exchange. However, some researchers have challenged this assumption. We conducted 12 groups of experiments using a 1/36-scale road-tunnel testing platform. We analysed three vehicle speeds and four roof-opening layouts. Supplemented by flow-field display technology, we tested the distribution of air velocities and the flow-field characteristics. Our major conclusions are as follows: (1) At a constant vehicle flow, the airflow at the roof opening was always from outside to inside, and no respiration phenomenon was observed. (2) The maximum inlet velocity was at openings near the tunnel entrance, and the velocity gradually decreased as the openings were placed deeper into the tunnel. The inlet velocity exhibited a concave curve along the tunnel length. (3) The number of roof openings had no significant impact on the inlet velocity, and it is inappropriate to treat the tunnel flow field as a conduit flow. (4) At a constant vehicle flow rate, roof openings provided a significant volume of ventilation, and the ventilation ability was different at different locations.

Influence of the vortex design method in the performance characteristics of reversible axial rotors

This paper presents a methodology for the aerodynamic design of reversible axial-flow rotors of jet fans, usually used for ventilation of road tunnels. Due to the low hub-to-tip ratio, typical of this kind of rotors, a particular type of non-free vortex is adopted to solve the radial equilibrium equation, in order to reduce the twist in the blades when compared to the free-vortex case. Values of the deviation and incidence angles, lift and profile drag coefficients, were interpolated from the literature data, for elliptical profiles with maximum aspect ratio of 8%. In order to reliably use these data in the computational routine, written in FORTRAN, for obtaining the main geometric and operational characteristics, a technique of scattered data interpolation was utilized. Radial basis functions (RBF) of type thin plate spline (TPS) were thus used for this purpose. This function showed to be efficient for the iterative procedure in the aerodynamic design of the rotor blades. Two reversible axial-flow rotors, formed by elliptical profiles, were finally obtained with the proposed methodology. The first profile resulted from the free-vortex condition and the second one from the non-free vortex condition. Both rotors have the same dimensions and the same number of blades, but differ in the stagger angle of each profile forming the blades. Through the use of the commercial code FLUENT, the main aerodynamic performance characteristics of these two rotors were determined, for a specific rotation, within a wide range of operation conditions. The non-free vortex rotor showed a higher maximum efficiency when compared to the free-vortex one, which was located in the region of stability of the rotor. On the contrary, the free-vortex rotor maximum efficiency was located in the region of instability of the rotor.

Model-based airflow controller design for fire ventilation in road tunnels

This paper describes a new approach to design the proportional-integral-derivative (PID) controller of the longitudinal airflow velocity in road tunnels for fire situations. Our work shows clearly that the use of a proper model provides valid data for model-based tuning of tunnel controllers, which is demonstrated by real tunnel tests. The design uses the simplified mathematical model of airflow dynamics based on Bernoulli and continuity equations, which describe the airflow dynamics in one dimension. Optimizing controller parameters on site is very time consuming and this problem increases in the case of complex tunnels with several entrance and exit ramps, which typically have occurrences of traffic congestion. Our approach is based on the design of the controller through simulations, which use the mathematical model of airflow velocity in the tunnel. This approach spares a lot of work and time with the controller tuning within tunnel tests. Moreover, it can discover potential problems, which can occur during real instances of fire in the tunnel. The additional advantage of this approach is a possibility to simulate a scenario of errors and failures of some devices, which are important for reliable control of longitudinal airflow velocity. Although this approach is focused primarily on complex road tunnels, due to their complexity and significant time savings with the controller tuning, it can be also used for simpler tunnels with no ramps (usually highway tunnels) where the design of the airflow controller is not as complex compared to the case of road tunnels. This paper also includes a case study of the airflow controller design for the Blanka tunnel complex in Prague, Czech Republic, which is the largest city tunnel in Central Europe.