Chris Graham, Carlos Mesa and Mark Gilbey presented at the ISAVFT 2015 - Symposium on Aerodynamics, Ventilation and Fire in Tunnels, held in Seattle, US on September 15-17, 2015.

1. Interaction between station openings
and environmental control systems
Chris Graham, Carlos Mesa, Mark Gilbey
WSP | Parsons Brinckerhoff in the UK

2. Context
• Review of recent work on a UK rail project
• Subsurface stations increasingly attractive due to
external pressures
• Reduce or make better use of land take
• Potential for commercial over site development
• Constrained by tunnel alignment
• Concerns over public amenity
• Strong preference for natural ventilation of large spaces
• Natural lighting provided through large openings

3. Station geometry
• Commuter rail service, shallow C&C construction
• Long rolling stock
• Train frequency demands multiple platforms
• Restriction on land take due to inner city location
• Desire for over site development improved land usage
• Visual effect of station for local stakeholders
• Provision of retail space

4. Problems faced
• Exposed location – potential for strong wind interactions
• Weather protection of openings
• Large irregularly shaped and dispersed openings
• Interactions with civil structure
• Isolation of tunnel piston airflow

5. Problems faced
• Exposed location – potential for strong wind interactions
• Weather protection of openings
• Large irregularly shaped and dispersed openings
• Interactions with civil structure
• Isolation of tunnel piston airflow

6. • Traditional louvres
– limit light
– resist natural ventilation
– Difficult to mount horizontally
– Adversely affected by wind if mounted vertically
• Clerestory vents
– Glazing encourages natural lighting
– Potential architectural feature
– Utilises wind to aid natural ventilation
• Consideration of predominant wind direction
• Considerations of challenging wind directions
Weather protection of openings

7. Weather protection of
openings
• Wind conditions
• 2m/s to 12m/s
• 4 cardinal directions to look
at effects under adverse
wind conditions
• Assumed uniform wind
profile, elevated vents

8. Problems faced
• Exposed location – potential for strong wind interactions
• Weather protection of openings
• Large irregularly shaped and dispersed openings
• Interactions with civil structure
• Isolation of tunnel piston airflow

9. Large irregularly shaped
and dispersed openings
• Clerestory vents not practical for large
openings
• Egregious support steelwork
• Construction costs
• Maintenance burden
• Large openings typically require
significant propping
• Unobstructed wind might recirculate
smoke
• Beams might be used to control wind
forces
• High aspect ration, hence transverse
wind is not likely to be an issue
• Only studied longitudinal wind
direction
• Adopted 12 m/s wind speed as a
challenging case
• Given low level, atmospheric boundary
layer profile used

10. Large irregularly shaped
and dispersed openings
• Large beam spacings predicted
negative flow (i.e. into station)
• Smaller beam spacings aid natural
ventilation and encourage flow out of
station.
• Improvements are predicted at beam
spacing of greater 30m
• No disbenifit was predicted for smaller
spacings

11. Large irregularly shaped
and dispersed openings
• Station environment might be isolated from
wind forces via active means
• Jet fans
• Air curtains
• Jet fans could be used to resist wind forces
• Modelled jet fans operating in the opposite
direction to wind
• Results showed a viable concept
• Difficulties arise:
• Control system
• Noise
• Maintenance
• Cost

12. Problems faced
• Exposed location – potential for strong wind interactions
• Weather protection of openings
• Large irregularly shaped and dispersed openings
• Interactions with civil structure
• Isolation of tunnel piston airflow

13. Isolation of tunnel piston
airflow
• Prevent recirculation of warm
tunnel air into adjacent bores
• Limit temperature pollution on
platforms from warm tunnel air
• Introduce ambient air into station
and outbound tunnel via openings
• Given high piston flows staggered
openings were beneficial
• High velocity air overshoots
openings immediately after
portal
• Staggered openings limits
recirculation between tunnels
• Further benefits realised by
providing dividing wall between
portals

14. Z=16mZ=3mY=30m CASE 1 CASE 2

15. Z=16mZ=3mY=30m CASE 3 + dividing wallCASE 3

16. Conclusions
• Care should be given to the configuration and size of large openings
• Passive means can be used to
– Provide wind force resilience
– Provide weather protection
– Maintain natural lighting and ventilation
• Structural elements may be complimentary to natural ventilation
• Jet fans could be used but concerns around practicality
• Location of openings at tunnel portals should consider both
– Momentum forces (piston effect)
– Buoyant forces
– Mixing between adjacent tunnels

17. Questions?