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Budownictwo Podziemne i Bezpieczeństwo w Komunikacji Drogowej i Infrastrukturze Miejskiej

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New Technologies applied to the design and optimization of tunnel ventilation systems

Ing. Justo Suárez

Area Manager - ZITRON

Dot. Ing. Massimiliano Bringiotti

Managing Director - GEOTUNNEL

Ing. Ana Belén Amado

Responsible of CFD and Virtual simulation - ZITRON

ABSTRACT: Construction of new transport infrastructures is being a social demand during

the last decades; therefore many countries have decided to carry out important investments

on this field. Among these transport infrastructures, road and railway tunnels and Metro lines

are the most significant ones.

The amazing improvements and fast growing technology in mechanized tunnel excavation

with TBM (Tunnel Boring Machine) has made possible the excavation of tunnels with several

tens of kilometers.

Subsequently, the technology applied in the electro-mechanic installations to be installed

in these tunnels, such as the ventilation, should also be improved. This is a serious challenge

in front of us, in order to provide safe and efficient solutions to new and complex problems

related to the passenger’s safety in these very long transport tunnels.

This paper is a general approach to the new technologies that are being currently applied

for the design and optimization of tunnel ventilation systems.

KEYWORDS: Tunnel, Ventilation system, Computational Fluid Dynamics, Fire, Safety.


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1. INTRODUCTION

During last years the length of the transport tunnels (Road and railway) has increased

significantly.

Not so long time ago, any tunnel over 2 km length was considered as a “long tunnel”.

Nowadays, tunnels over 10, 20 even 40 kms are being constructed and some of them are

already in operation.

Technology for the construction of these “long tunnels” has also developed tremendously.

The use of TBM is now considered as the “standard” method of excavation, so there is almost

no limitation on the length of the tunnels to be excavated.

In parallel, the electro-mechanic installations for these new “very long” tunnels should be

improved and adequate rapidly to the new tunnel conditions (long tunnel distances, very high

volume of traffic and passengers simultaneously in the tunnel,…) otherwise we could arrive

to the following paradoxical situation: the length on the new tunnels to be constructed will be

restricted, not due to limitations on the tunnel construction technology, but because the

electro-mechanic installations will not able to satisfy minimum conditions of comfort and

safety for the passengers.

Among all the electro-mechanic installations in a tunnel (lighting, communication system,

video and surveillance system, fire detection and extinguish system,…), the ventilation is one

of the critical ones.

Ventilation system in a tunnel (road and railway) is directly related to the comfort and

safety of the passengers. Additionally, from an electrical point of view, ventilation is the

most energy demanding system. Therefore, the design of a safe and high efficient ventilation

system becomes a very important task to be studied carefully.

To achieve this goal, new technologies, such as CFD (Computational Fluid Dynamics),

3D scanners, should be applied to fan design. Also, to verify this optimised design, fan

manufacturers should offer the possibility of aerodynamic fan testing at real scale and full

power.

2. BASIC PRINCIPLES FOR FAN DESIGN

The main input data for the aerodynamic fan design are: duty point/s (Air Flow Vs

Pressure), efficiency and reversibility


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Based on the above data, fan designers should carry out the fan selection, which means to

select the most aerodynamically optimised and less power consuming fan that satisfies these

requirements.

This is a challenging work that involves the mechanical design of all different fan

elements. Among all of them, impeller and guide vanes are the most affecting ones to the fan

performance (Air flow and Pressure) and to the motor consumption (efficiency).

The aerodynamic profile of the impeller blades and guide vanes should be designed to

optimize the fan aerodynamic performance at minimum power consumption.

The objective is to achieve the highest lift force (FL) with the lowest drag force (FD).

Figure 1. Layout showing Drag and lift forces

When the blade angle of attack is adjusted to “move air”, a force (F) is affecting the

blade.

This force F can be divided into two main components, one in the same direction as the

air, called “drag force” (FD), and another with perpendicular direction, called “lift force”

(FL).

The shape of the upper part of the blade causes an increase in the air velocity locally and

therefore a reduction in static pressure, generating then lift force.

If the angle of attack is increased in exceeds about 20º (depending the blade profile)

a severe flow separation occurs, and the drag force increases rapidly, this phenomenon is

known as “stalling”.

Another general rules to take in account in fan design are:


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• Number of impeller blades: More blades → More pressure

• Impeller diameter: Bigger impeller diameter → More air flow

• Hub diameter: Bigger hub diameter → Lower air flow and higher pressure

3. COMPUTATIONAL FAN AERODYNAMIC DESIG (NUMECA®)

The modern fan design is assisted by CFD (Computational Fluid Dynamics) technology.

One of the most powerful software on this filed is NUMECA®.

As a developing science, CFD (Computational Fluid Dynamics) has received extensive

attention throughout the international community since the advent of the digital computer.

CFD interests are mainly driven by the desire to model complex physical fluid phenomena,

which couldn't be easily or cost effectively, simulated with a physical experiment.

Computational techniques differ from analytical or theoretical solutions in the sense that

they only solve equations at a finite number of points rather than for the entire flow field.

Choosing these points, of the entire flow field, may become quite difficult, especially for

a complex geometry, and it may require hundreds of thousands or even million of points. In

general, a dense grid with many points will give a solution of great detail, but require more

computer resources and time to reach a solution. Since a compromise between computer

resources and solution quality is required, the current trend is often to use a dense grid in

areas where the solution may change rapidly such as in the boundary layer or near a shock

wave, but the use of a coarser grid with fewer computational points in areas where the

solution is expected to change more gradually.

The resolution of Computational Fluid Dynamics (CFD) problems involves three main

steps: spatial discretization of the flow domain, flow computation and results visualisation.

3.1. Example of application

CFD was used to obtain the performance characteristic curve of a new fan model

previously selected, with the following main features: fan diameter (Ø 2000 mm); hub

diameter (Ø 1200 mm); power (160 kW) and rotation speed (990 r.p.m - 50 Hz - 6 poles

motor)

To prepare the geometrical model used in the CFD simulations the fan is divided into 2

different parts: Rotor (Impeller) and Stator


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Rotor

This part includes the rotating part of the fan, that means,

rotor block has been used the following data: Fan d

(Ø1200 mm), quantity of blades (12) and tip clearance (

the blade profile in 3D format.

Figure 2. 3D impeller blade profile, showing pressure side and suction side

Stator

This block simulates the static part of the fan, downstream of the impeller.

the main element are the guide vanes. To generate the

following data: fan diameter (Ø 2000 mm), hub diameter (

vanes (11). Also the guide vane profile is generated in 3D forma

Figure 3. 3D guide vane profile. Left is pressure side and right is suction side.

ństwo w Komunikacji Drogowej i Infrastrukturze Miejskiej

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includes the rotating part of the fan, that means, the impeller. To generate the

been used the following data: Fan diameter (Ø 2000 mm), hub diameter

(12) and tip clearance (7 mm). The first step is to generate

Figure 2. 3D impeller blade profile, showing pressure side and suction side

This block simulates the static part of the fan, downstream of the impeller. In this block

the main element are the guide vanes. To generate the stator block, it was necessary the

fan diameter (Ø 2000 mm), hub diameter (Ø1200 mm) and quantity of guide

Also the guide vane profile is generated in 3D format.

Left is pressure side and right is suction side.


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3.1.1. Step 1: Spatial discretization of the Air Flow D

The quality of the grid is definitely important, since it strongly influences the solution

including whether or not a solution can be found at all. What determine the grid quality are

mainly two parameters: level of skewness (or orthogonality)

It is important to minimize the number of cells (finite elements)

skewness (cells with very low internal angles) because the calculation of fluxes can become

significantly erroneous under such conditions. By other hand, it is particularly important, in

regions of high gradients, such as boundary layers, free shear

expansion ratio (the ratio of adjacent cell side) within an absolute range of about 0 to 1.6.

To achieve a good grid quality in all Air Flow D

of the total domain (rotor and stator) into smaller blocks.

The mesh and the shape of some of these block

Figure 4. Spatial discretization of several blocks of Air Flow Domain on the rotor part

3.1.2. Step 2: Flow Model

To define the project flow model, it is necessary to choose:

model. The fluid model used in these simulations is

(heat conduction, dynamic viscosity, temperature,…). Also, it is chosen a turbulence model

that simulates the behaviour of complex flows.

3.1.3. Step 3: Flow equation resolution and boundary conditions

The process to obtain the complete fan performance curve involves also several

equations that have to be solved for different values of flow rate, so i

many calculations as fan performance points (Flow Vs


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Air Flow Domain

The quality of the grid is definitely important, since it strongly influences the solution

hether or not a solution can be found at all. What determine the grid quality are

evel of skewness (or orthogonality) and expansion ratio.

number of cells (finite elements) containing a high level of

skewness (cells with very low internal angles) because the calculation of fluxes can become

significantly erroneous under such conditions. By other hand, it is particularly important, in

regions of high gradients, such as boundary layers, free shear-layers and shocks, to keep the

expansion ratio (the ratio of adjacent cell side) within an absolute range of about 0 to 1.6.

Air Flow Domains, it was necessary divide each part

aller blocks.

blocks are shown in the following figures.

Figure 4. Spatial discretization of several blocks of Air Flow Domain on the rotor part

el, it is necessary to choose: fluid model and turbulence

used in these simulations is air with the specific physical properties

(heat conduction, dynamic viscosity, temperature,…). Also, it is chosen a turbulence model

boundary conditions

the complete fan performance curve involves also several flow

have to be solved for different values of flow rate, so it is necessary to run as

as fan performance points (Flow Vs Pressure).


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Also boundary conditions have to be set, such as: inlet mass flow corresponding to the

flow rate that will be calculated, outlet static pressure corresponding to atmos

pressure and rotational speed corresponding to motor speed.

3.1.4. Step 4- Results: Predictive Fan Characteristic Curve

results.

Once the CFD simulation is carried out, the predictive fan

Figure 5. Final results for fan simulation and predictive fan performance curve

Although the aim of this computer simulation is to obtain the predictive fan characteristic

curve, it is also very interesting to analyse other

the flow solutions by means of CFD allows to obtain, such as 2D and 3D images of pressure

and velocity distributions, vector fields, flow lines or turbulence inside of the flow domain.

Figure 6. Static pressure distribution


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Also boundary conditions have to be set, such as: inlet mass flow corresponding to the

flow rate that will be calculated, outlet static pressure corresponding to atmospheric static

pressure and rotational speed corresponding to motor speed.

Predictive Fan Characteristic Curve, post-processing and graphic

predictive fan performance curve is obtained.

fan simulation and predictive fan performance curve

computer simulation is to obtain the predictive fan characteristic

other graphic results that the post processing of

obtain, such as 2D and 3D images of pressure

velocity distributions, vector fields, flow lines or turbulence inside of the flow domain.

Figure 7. Air flow lines along the fan


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4. BLADE VERIFICATION WITH A 3D SCANNER

To achieve a good performance and high efficiency values on a fan, the impeller blades

should be well design and optimised. To make effective this

should be verified, checking that their shape is

shape. A 3D scanner should be applied to achieve this goal.

This verification has two steps: 3D scanning of the blades

to verify that the real (scanned) blades and the theoretical blades

Figure 8. Step 1- 3D blade scanning

Figure 9. Step 2 - Blade comparison (real scanned Vs theoretical)

5. FACTORY TESTS

5.1. Aerodynamic fan test

The objective of this tests is to verify that the manufactured fan achieves the predictive

performance curve (Flow Vs Pressure) obtained previously by means of NUMECA software.

During this test it is also verified fan efficiency, power consumption, noise leve

vibration values.


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ITH A 3D SCANNER

achieve a good performance and high efficiency values on a fan, the impeller blades

To make effective this virtual design, the real blades

that their shape is inside tolerance with the designed blade

achieve this goal.

3D scanning of the blades and shape comparison software

the real (scanned) blades and the theoretical blades are identical.

Blade comparison (real scanned Vs theoretical)

objective of this tests is to verify that the manufactured fan achieves the predictive

performance curve (Flow Vs Pressure) obtained previously by means of NUMECA software.

During this test it is also verified fan efficiency, power consumption, noise level and


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These tests are carried out according to international recognised standards, such as

AMCA (Air Movement and Control Association).

Figure 10. Layout of Aerodynamic test bench accredited by AMCA.

Any deviation or possible problem would be detected during this test and corrected before

fan delivery.

5.2. High temperature fan test

Fans used in emergency tunnel ventilation systems should be able to operate in high

temperature conditions, in case of fire.

To certify that the fans are able to operate properly under high temperature conditions is

required to carry out a test.

These high temperature tests have to be carried out in accredited laboratories, according

to European standard EN 12101-3. The following minimum condition should be observed

during test performance:

• The fan should be able to operate at the high temperature (up to 400 ºC) during a period

of 120 minutes.

• Heat up ramp from ambient temperature to test temperature must be achieved in short

time, that is within 5 and 10 minutes.

• After 15 minutes running the high temperature test, the fan has to afford being switched

off (during 2 minutes) and restarted again.

• The average value of the fan air flow during the high temperature period must be in the

range of the nominal values (not beyond of 10% difference).


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Figure 11. Photo and scheme of high temperature test bench for tunnel axial fans

6. OPTIMIZATION OF COMPLETE VENTILATION SYS

Simulation of tunnel ventilation systems is challenging both

physics involved and the large domain sizes required for tunnels that may run for several

kilometres. Even so, comparison with physical testing results shows that computational fluid

dynamics (CFD) can accurately simulate flow patter

length. Continual improvements in CFD software and high performance computing hardware

have made it possible to optimise the design of

systems.

One of the most powerful and commonly used CFD for tunnel ventilation is FLUENT

Given the size and complexity of tunnel geometry, it is difficult

and test scale models to evaluate potential ventilation system designs. Simulation makes it

possible to evaluate the performance of alternative configurations and to

system should be operated under normal and emergency conditions

a lower cost.

Figure 12. Graphical result of FLUENT® simulation in a tunnel ventilatio


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. Photo and scheme of high temperature test bench for tunnel axial fans

LETE VENTILATION SYSTEM USING CFD (FLUENT®)

Simulation of tunnel ventilation systems is challenging both because of the complex

physics involved and the large domain sizes required for tunnels that may run for several

kilometres. Even so, comparison with physical testing results shows that computational fluid

dynamics (CFD) can accurately simulate flow patterns and pressure drop in tunnels of any

length. Continual improvements in CFD software and high performance computing hardware

optimise the design of increasingly challenging tunnel ventilation

commonly used CFD for tunnel ventilation is FLUENT®.

unnel geometry, it is difficult and expensive to build

ventilation system designs. Simulation makes it

performance of alternative configurations and to determine how the

emergency conditions — all in less time and at

simulation in a tunnel ventilation system


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Fire simulations using CFD software are useful for optimization and validation of tunnel

ventilation systems. A fire growth model is defined within the tunnel in a location

strategically chosen to account for worst-case conditions. The designed tunnel ventilation

system is activated with a chosen time delay from the moment that fire starts. The simulation

predicts the performance of the ventilation system in order to control the smoke towards the

fumes exhaust areas and prevent the back-layering effect.

The passenger evacuation areas in the tunnel should be kept smoke-free during the

assumed evacuation time. Other key simulation outcomes are velocity distribution and

temperature maps along the tunnel.

In CFD simulation, meshing is a very important issue, particularly in our case of tunnels

that can extend several kilometres. There are critical areas, such as the fire location and the

areas upstream/downstream of fans, where the mesh must be fine to accurately capture the

physics. In other areas, cells can be larger to reduce the total cell number and reduce the

computational and processing time.

Accurate simulation of a tunnel ventilation system today typically requires about

1 million cells per kilometre of tunnel. High-performance computing and recent advances in

parallel algorithms have enabled quasi-linear scalability of fluid dynamics calculations.

Continual development in both hardware and ANSYS FLUENT software have contributed,

and will continue to contribute, in solving more complex and higher fidelity tunnel

ventilation systems. High-performing hardware allows the clustering of processing units in a

cost-effective way, while more efficient computational methods permit prediction of more

complex physical phenomena in longer tunnels. The final result is an accurate simulation of

complex tunnel ventilation systems in less computational time.

7. CASE STUDY: VENTILATION SYSTEM FOR GUADARRAMA TUNNELS (2X28

KM)

Guadarrama tunnels are the most important infrastructure on the high speed railway line

between Madrid and the north-west region of Spain. They are the fifth longest tunnels in the

world and entered into service on 23rd December 2007.

They consist in two parallel tubes, one for each direction in which the high speed train

runs, with a length of 28.4 kms and a section of 52 m2.

The most innovative characteristic of Guadarrama tunnels is the fact that the excavation

was made with 4 TBMs starting simultaneously from the tunnel portals and breaking through


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at approx. 15 kms inside the mountain, that means there is not any intermediate shaft or

access galleries. This is something unique for this kind of very long tunnels. From one side,

the excavation costs and time of construction is reduced significantly, but on the other hand,

the design and installation of an effective ventilation system becomes a very difficult and

challenging task.

The tunnels are interconnected by means of emergency passageways every 250 m and

a 500 m long emergency area, located at an equidistant point from both tunnel port

case of tunnel evacuation, this emergency area can hold up to 1200 people

Originally, the emergency ventilation system was designed considering two main

ventilation plants located at both tunnel ends, with closing doors at the tunnel entrances, i

order to pressurise one of the tunnels, in case of emergency (i.e. a fire event) in the other

parallel tunnel.

However, after a detailed risk analysis of this original ventilation design, it was decided

to reject it, due to the problems associated with a

of the doors and the catastrophic effects in case of crashing the high speed train at over 250

km/h.

Subsequently, it was decided to carry out a complete re

ventilation system.

The idea was to replace the tunnel doors by a pneumatic closure system using jets of air.

The key point for a successfully re-design of the emergency ventilation system was the

use of CFD (Computational Fluid Dynamics).

Using this innovative technology, it was possi

in order to achieve the most effective design for the tunnel ventilation system.

The civil construction of all structural elements involved in the tunnel ventilation system,

have been carried out following strictly the results of the CFD simulations.

Figure 13. CFD meshing model Vs real photo of the subsequent


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hat means there is not any intermediate shaft or

access galleries. This is something unique for this kind of very long tunnels. From one side,

the excavation costs and time of construction is reduced significantly, but on the other hand,

tallation of an effective ventilation system becomes a very difficult and

The tunnels are interconnected by means of emergency passageways every 250 m and

a 500 m long emergency area, located at an equidistant point from both tunnel portals. In

case of tunnel evacuation, this emergency area can hold up to 1200 people

Originally, the emergency ventilation system was designed considering two main

ventilation plants located at both tunnel ends, with closing doors at the tunnel entrances, in

order to pressurise one of the tunnels, in case of emergency (i.e. a fire event) in the other

However, after a detailed risk analysis of this original ventilation design, it was decided

to reject it, due to the problems associated with a possible failure in the opening and closing

of the doors and the catastrophic effects in case of crashing the high speed train at over 250

Subsequently, it was decided to carry out a complete re-design of the emergency

as to replace the tunnel doors by a pneumatic closure system using jets of air.

design of the emergency ventilation system was the

Using this innovative technology, it was possible to perform several computer simulations

in order to achieve the most effective design for the tunnel ventilation system.

The civil construction of all structural elements involved in the tunnel ventilation system,

ly the results of the CFD simulations.

the subsequent ventilation constructions


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It should be especially remarked the optimization in the air flow injection angle of the

Saccardo nozzle located at the top of the false tunnels constructed on the four tunnel portals.

Figure 14. CFD meshing model Vs real photo of Saccardo nozzles located above tunnel portals.

LITERATURE

[1] European standard EN 12101-3 “Smoke an heat control system

for powered smoke and heat smoke ventilators”.

[2] “Fire and Smoke control in road tunnels”. PIARC committee in road tunnels (C5)


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It should be especially remarked the optimization in the air flow injection angle of the

f the false tunnels constructed on the four tunnel portals.

real photo of Saccardo nozzles located above tunnel portals.

3 “Smoke an heat control system – Part 3: Specification

for powered smoke and heat smoke ventilators”.

“Fire and Smoke control in road tunnels”. PIARC committee in road tunnels (C5)

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