Jet Fan Research Articles

네트워크형 지하 도로터널 분기부에서의 환기효율 향상방안에 대한 실험적 연구

네트워크형 도로터널 내 분기부 구조물과 제트팬에 의한 분기 환기효율 분석하고자 실제 도로터널을 1/45로 축소하여 실험을 수행하였다. 차량이 주행할 때 발생하는 교통관성력을 적용하기 위해 블로워 팬를 사용하여 축소모형 터널내 기류를 형성하였고, 터널의 국부적인 위치에서 속도를 측정하여 분기 효율을 연구하였다. 구조물의 특징으로 발생되는 환기 저감을 개선하기 위해 제트팬을 설치하여 터널 내 환기 효율을 최적화하였다. The experiment was performed to analyze the intersectional ventilation efficiency by intersection structure and Jet Fan in network-form road tunnel. For this, the size of real road tunnel was reduced by 1/45. To apply traffic inertia force when driving, blower fan was used to form an airflow in model tunnel and the intersectional efficiency was also investigated by measuring the speed at local point of the tunnel. To improve the reduction of ventilation caused by the structure character, Jet Fan was installed to optimize ventilation efficiency in tunnel.

Smoke control in case of fire in a large car park: CFD simulations of full-scale configurations

Computational Fluid Dynamics (CFD) simulation results are presented of full-scale car park fire experiments with smoke and heat control (SHC) by forced mechanical horizontal ventilation. A well-controlled liquid pool fire heat release rate (HRR) is set as an input parameter. The effect of the SHC system on the smoke movement in fire conditions is examined. The following parameters are varied: fire HRR; smoke extraction flow rate; openings for incoming air (so that different flow patterns have been created); presence of beams. The impact of jet fans (induction type) is also addressed in a number of simulations. The trends observed in the full-scale experimental campaign are well captured and additional insight is provided for the interpretation of the results. The sensitivity of the CFD results to input parameters is highlighted. For a 4MW HRR fire, which is the order of magnitude for a car fire, the required ventilation velocity to limit smoke back-layering in a flat ceiling car park is around 1.1m/s. When beams are present, the average velocity must be higher, particularly for longitudinal beams. If smoke is trapped inside a recirculation region, increasing the smoke extraction rate does not help to remove the smoke.

Numerical Study on Effects of Induced Velocity on Central Extraction System in Large Tunnel Fire

Abstract The effects of different induced velocities on the central extraction system for a tunnel are investigated for a 100MW fire scenario. Computer modeling is used for the investigation with a numerical simulation method. The selection of five different induced velocities is evaluated and compared. The smoke control strategy in this study is downstream dampers in the vicinity of fire site opened with number of three and the upstream jet fans supplying airflow as the induced velocity. Distributions of smoke propagation, temperature and visibility in variation of induced velocities are analyzed. The results show that larger induced velocity is needed to restrict smoke to the region between the fire site and the damper openings for safe evacuation. Additionally, the gradients of upstream temperature decreases as the induced velocity increases. The results also suggest that the impacts of the induced velocity on the upstream visibility have a correlation with the back layering.

Numerical Simulation for Part Effect of Ventilation of Extra-Long Road Tunnel

Er Lang Shan tunnel is the most absolute altitude constructed highway tunnel in china, which is firstly used the semi-transverse ventilation system, is characteristic of extensive length, higher absolute altitude, multivariate climate, two-way traffic and complex wind stream. Based on FEM software CFDesign, the distributed losses, the conflux losses and the shoot of jet fans in the semi-transverse ventilation system of Er Lang Shan highway tunnel are studied by numerical simulation. Part resistance coefficients that numerical simulation of the semi-transverse Ventilation under various work condition needs are obtained.

Numerical Simulation on Fire Smoke Flow with Jet Fans in an Underground Garage

With the aim of evaluating capabilities of a ventilation system with jet fans to control fire smoke in an underground garage, we carried out a set of FDS simulation. According to the results, temperature and soot density of fire has reduced within an acceptable range. We believe that the ventilation system based on the jet fans has indeed controlled fire smoke effectively, thereby we have enough time for safety rescue.

터널 환기용 제트홴의 성능 향상을 위한 수치최적화

This paper presents an optimization procedure for performance improvement of a tunnel ventilation jet fan. Optimization techniques based on response surface approximation (RSA) are employed to improve the aerodynamic performance of a tunnel ventilation jet fan. For numerical analysis, three-dimensional Renolds- averaged Navier-Stokes (RANS) equations with shear stress transport turbulence model are discretized by using finite volume approximations and solved on hexahedral grids to evaluate the total efficiency at the operating condition as the objective function. Four geometric variables defining the meridional length and the thickness profile at the hub and shroud in the jet fan rotor are selected as design variables for the numerical optimization. The results of the numerical optimization show that the total efficiency of the optimized model is significantly improved in comparison with the base model.

A Study on Large Power Jet Ventilation Technology in Long Tunnel Construction

One of difficulties in super long tunnels’ construction is the construction ventilation to meet the requirement of normal construction environment and assure the workers’ health. Using traditional tunnelling ventilation is very difficult to meet the need of super long tunnel construction. As the energy assumption is high and it is very expensive. This paper investigated the simulation of tunnel construction ventilation with large power jet fans during the construction of Jinping Auxiliary Tunnels by using the computational fluid code FLUENT, the layout of jet fans in the tunnels is optimized. It is found that the best layout of the jet fan is aroud the transverse channel under the direction of airflow and jet fan should not be too far away from the transverse channel. The CO mainly distributes in the upper part of the tunnel when the jet fan is installed at a higher position, this layout of the jet fan is beneficial to construction of tunnels.

제트홴의 이격거리에 따른 터널내 환기특성에 관한 수치적 연구

The jet fan is generally used to add thrust in the longitudinal ventilation system of road tunnel and the geometric conditions of jet fan such as the distance from tunnel wall have an effect on the performance of ventilation system. Numerical analyses on the flow in tunnel caused by operation of jet fan are presented to study the ventilation characteristics in tunnel. While the distance between jet fans in parallel installed in tunnel is changed 0.5 L/D to 3.0 L/D, the flowrate and mean velocity through tunnel are calculated for each cases. As the distance between jet fans increases, the flowrate through tunnel increases asymptotically and the momentum of tunnel flow is alike.

Impact of location of jet fan on airflow structure in tunnel fire

Airflow structure and its magnitude are important for smoke management in longitudinally ventilated tunnels. This paper presents a sensitivity study by Computational Fluid Dynamics technique, which considers different dimensions, orientations and the natures of fire source. Its impact on the airflow velocity and temperature distribution is investigated with various locations of fan group activated. A theoretical correlation between the distance of active fan group from the fire source and the upstream velocity is proposed individually for pool fire and solid fire. It reveals that the nature of the fire source imposes adverse effect on the upstream air velocity and the airstream pattern over the entire tunnel. The upstream velocity remains fairly constant when the active fan group is located 200 m or beyond from a vehicle fire that occupies a significant cross-sectional area of tunnel.

Reliability estimation of auxiliary ventilation systems in long tunnels during construction

Ventilation system should blow large quantity of airflow particularly in case of toxic or explosive gasses emission from the wall rocks and face, especially in long tunnels. In these cases, multiple jet fans are usually required, so that they could be grouped together as serial, parallel or combined arrangements through ventilation system or equally spaced along the tunnel. There is a serious requirement to have some reserved jet fans along with the main once, so that the operation of the ventilation system could be reliable. Operation of a ventilation system is usually evaluated by experiences and engineering judgments which follow empirical methods. The aim of this paper is to introduce an approach to evaluate reliability of ventilation system in the long tunnels. The method is based upon using the failure rate time to determine the probability of the failure of an active jet fan and also the repair rate time to determine the probability of repairing the out of work ones .In this approach, the active and standby jet fans are modelled as a stochastic process. Therefore, the probability of replacing each failed jet fan with a standby jet fan is estimated using Markov Chains theory .From this point of view a more realistic decision-making for the number of standby jet fans and also reducing the risk as well as uncertainties can be based upon the analysis of such a results.

Fluent Based Numerical Analysis of Eliminating Ultra-Limit Gas in Upper Corner by Using Rotary Jet Fan

For the problem of gas accumulation in upper corner of "U" type ventilation system mining face, a new approach to eliminating gas accumulation in upper corner of coal mining face by using high-speed rotating jet is proposed based on flow law of rotary jet and actual environment of coal mining face. The numerical simulation with Fluent software is carried out. The results show that when fan is mounted close to the wall, the high-speed rotating jet has good Coanda effect, little impact on air flow structure of coal mining face, and is significantly effective to deal with gas accumulation in upper corner. FLUENT based numerical simulation provides a theoretical basis for actual application of rotary jet fan in coal mining face.This template explains and demonstrates how to prepare your camera-ready paper for Trans Tech Publications. The best is to read these instructions and follow the outline of this text.

Numerical Study on Impulse Ventilation for Smoke Control in an Underground Car Park

This study examines smoke control capacity of impulse ventilation system (IVS) in an underground car park. An analysis is made in relation to important parameters including jet fan number, jet fan velocity, extract rate and system robustness on fire position. The comparison with ductwork system is also performed to determine the different effect of smoke control between two systems. Fire Dynamic Simulator version 5.30 is applied to simulate 10 scenarios in a 80 m long, 40 m wide and 3.2 m height domain witha fire source simulating a car fire with an peak heat release rate of 4 MW. Results show that impulse ventilation system not noly prohibit fire smoke spreading but also maintain a good visibility providing clear access for fighters. However it may cause temperature rise on the downwind zone of fire source with a maximum value between 80-100 and fire plume e tilt. Smoke control capacity of impulse ventilation system is sensitive to jet fan numbers. Too high jet fan velocity may cause severe smoke recirculation. Increment in extract rate is conductive to relay jet flows. An impulse ventilation system can effectively control smoke movement and induce smoke to extract points under two typical different fire locations, which is of great practical importance. Impulse ventilation system seems superior to ductwork system in maintaining high visibility.

Time-dependent Multiscale Simulations of Fire Emergencies in Longitudinally Ventilated Tunnels

This paper applies a novel and fast multiscale approach to model ventilation flows and fires in tunnels. The complexity and high cost of full CFD models and the inaccuracies of simplistic zone or analytical models are avoided by efficiently combining mono-dimensional (1D) and CFD (3D) modelling techniques. The multiscale model couples a 3D-CFD solver with a simple 1D model allowing for a more rational use of the computational resources. The 1D network models tunnel regions where the flow is fully developed (far field), and detailed CFD is used where flow conditions require 3D resolution (near field). The multiscale method has been applied to model steady-state fires and tunnel ventilation systems, including jet fans, vertical shafts and portals, and it is applied here to study the transient flow interactions in a modern tunnel of 7 m diameter section and 1.2 km in length. Different ventilation scenarios are investigated to provide the timing to reach the critical velocity conditions at the seat of the fire and to remove the upstream back layering. The much lower computational cost proofs of great value, especially for parametric and sensitivity studies required in the design or assessment of real ventilation and fire safety systems. This is the first time that a comprehensive analysis of the transient fire and ventilation flow scenarios in a long tunnel is conducted

Time-dependent Multiscale Simulations of Fire Emergencies in Longitudinally Ventilated Tunnels

This paper applies a novel and fast multiscale approach to model ventilation flows and fires in tunnels. The complexity and high cost of full CFD models and the inaccuracies of simplistic zone or analytical models are avoided by efficiently combining mono-dimensional (1D) and CFD (3D) modelling techniques. The multiscale model couples a 3D-CFD solver with a simple 1D model allowing for a more rational use of the computational resources. The 1D network models tunnel regions where the flow is fully developed (far field), and detailed CFD is used where flow conditions require 3D resolution (near field). The multiscale method has been applied to model steady-state fires and tunnel ventilation systems, including jet fans, vertical shafts and portals, and it is applied here to study the transient flow interactions in a modern tunnel of 7 m diameter section and 1.2 km in length. Different ventilation scenarios are investigated to provide the timing to reach the critical velocity conditions at the seat of the fire and to remove the upstream back layering. The much lower computational cost proofs of great value, especially for parametric and sensitivity studies required in the design or assessment of real ventilation and fire safety systems. This is the first time that a comprehensive analysis of the transient fire and ventilation flow scenarios in a long tunnel is conducted

제트홴 소음기 형상이 성능에 미치는 영향

In this paper, a numerical study has been carried out to investigate the influence of silencer design variables on the performance of a jet fan. In order to achieve an optimum jet fan design and to explain the interactions between the different geometric configurations in the jet fan, three-dimensional computational fluid dynamics and the Design of Experiments method have been applied. Two geometric variables, i.e., cap size and silencer length, were employed to improve the performance of the jet fan. The objective functions of the jet fan are defined as the effective velocity and total efficiency at the operating condition. Based on the results of computational analyses, the flow characteristics were discussed. The effect of silencer with a specific roughness on the performance was also discussed.

Modelling and simulation of a jet fan for controlled air flow in large enclosures

Jet fans are applied for control of air flow and support of pollutant dispersal in large enclosures. In The Netherlands, application is well known for car parks as part of the fire safety design. In the design phase often the Computational Fluid Dynamics (CFD)-technique is used to verify the fire safety level afforded by the application of jet fans. However, very little is known on the modelling requirements of jet fans in CFD. This includes paucity on experimental data that can be applied for validation of the jet fan model. In this study results are presented as measurements for a specific type of jet fan in a large enclosure and of validation of modelling characteristics of the jet fan in CFD. Both free and near-wall positioning have been investigated and a modelling proposal is made. For the modelling of the jet fan, point-of-departure is a low complexity, as the model generally will have to be included in large computational domains. Applicability of the developed approach and assessment of efficiency of jet fan positioning in large enclosures is shown through a case study.

제트홴에 의해 형성되는 터널내 유동의 실험 및 수치적 해석

To analyze the three-dimensional flow in tunnel caused by operation of jet fan, both experimental and computational studies have been conducted. The experimental analysis of tunnel flow induced by jet fan is conducted on a real-scale apparatus with jet fan and tunnel, and air velocity at the monitoring points is measured for variation of fan`s RPM. The three-dimensional numerical analysis including tunnel and jet fan is carried out for the same geometric configuration as the experimental analysis. The experimental and computational results are compared to examine the applicability of the numerical method.

Analysis of the ventilation systems in the Dartford tunnels using a multi-scale modelling approach

The capabilities of the ventilation systems in the two road tunnels at Dartford (UK) are analysed using a multi-scale modelling approach. Both tunnels have complex semi-transverse ventilation systems with jet fans to control longitudinal flow. The construction and ventilation systems in the tunnels are described and the current emergency ventilation strategies are presented. The analysis includes a coupling of a 1D network model with 3D components, representing the operational jet fans, built using computational fluid dynamics. The jet fans were experimentally characterized on-site and the findings were compared to the model predictions. The predicted ventilation flows for each of the emergency ventilation strategies are presented and discussed. In cold-flow conditions, ventilation velocities significantly above 3 m/s can be generated throughout the tunnels. However, it is observed that 1/3 of the flow generated in the East tunnel is diverted from the tunnel up the extract shafts. The model was used to simulate various reduced fan combinations and thus the level of redundancy in each of the systems has been estimated. It is found that an acceptable level of ventilation may be produced in the West tunnel, even if several pairs of jet fans are disabled. In the East tunnel there is less redundancy, but an acceptable level of ventilation control can be maintained with one or two jet fans disabled.

Computational study of effects of jet fans on the ventilation of a highway curved tunnel

A computational study was carried out to investigate the aerodynamic behavior of jet fans in a curved road tunnel and its effects on the tunnel ventilation system. It has been found that the variations of the static and dynamic pressure in a curved tunnel are non-monotonic. After the issue of the jets, the pressure initially increases gradually, but this is followed by a sudden drop and then a recovery. This is attributed to the interaction between the jets and the curved walls of the tunnel. A sudden increase in pressure is resulted as the jet reaches the convex wall, whereas that the concave wall is approached causes a pressure reduction. The flow becomes asymmetrical downstream of the jets. The development of the jets depends on the separation of the fans and the distance between the fans and the tunnel walls. Increasing the space between the fans or moving them away from the tunnel ceiling makes the jets spreading more quickly across the cross-section. However, it takes a longer distance for the jets to develop when the fans are close to each other or to the tunnel wall. The distance required for pressure to be fully recovered is approximately 90–120 m in this study. The biggest pressure-rising coefficient is obtained when the fans are arranged according to the distance of 2.4 m between the fans, the fans offset of 0.5 m from the centre line towards the convex wall, and the ratio of the distance between fans and the ceiling to the diameter of fans of 1.77.

Fluid dynamic performances of traditional and alternative jet fans in tunnel longitudinal ventilation systems

This paper presents the results of a numerical investigation carried out on an alternative jet fan, known in literature like Banana Jet®, and it compares its fluid dynamic performances to traditional axial ventilation systems. The alternative jet fan is equipped with inlet/outlet sections inclined at a fixed pitch angle ( α) toward the tunnel floor. This approach establishes an alternative solution that is able to provide a safety level equivalent to the traditional solution, in different scenarios. Both systems are installed in an one-way tunnel and two different scenarios (without vehicles and with traffic jam) are considered, in event of fire. The fire was simulated setting heat flux on Heavy Good Vehicle (HGV) surface and comprehensive of radiative heat flux. Computational Fluid-Dynamic (CFD) are applied to simulate the ventilation in the unidirectional tunnel through k– ε model, including temperature fields. The results show, for both scenarios, the existence of an optimal pitch angle which offers advantages in comparison with the traditional system ( α = 0°) in terms of plant and running costs. In the next paper, the influence of the radiative heat flux for the optimal pitch angle will be explicitly considered.