Decapitations

[TheSlash]

Everyone knows there's no suchh thing as the suction effect.

It must be my imagination everytime a train goes by then

 

[Gizmogle]

Ok, but do you do it? some people just take it a little bit over the top

I do Yes. I do agree though, some people do take it over the top lol

 

[AlexS]

It must be my imagination everytime a train goes by then

Wembley Central's fast line platforms are closed off off peak for fun too!

 

[Nick W]

It must be my imagination everytime a train goes by then

I feel a wind almost parallel and slightly away from the train that blows things down the platform. Don't go too close in case you fall over and roll off though.

Dunno where the suction effect came from.

 

[TheSlash]

The suction effect is after the train passes. The longer the train, the higher the speed and the more confined the space, the more the effect.
Try standing in Micheldever tunnel with a fully loaded Freightliner going through at 75mph.

 

[Nick W]

The suction effect is after the train passes. The longer the train, the higher the speed and the more confined the space, the more the effect.
Try standing in Micheldever tunnel with a fully loaded Freightliner going through at 75mph.

You're right, there is a suction effect in tunnels. Perhaps that's what started the suction effect on platforms myth.

 

[Zamracene749]

Suction effect is very real.

The train moves air along with it at a much higher speed than the surrounding air. Any moving fluid/object will present a lower pressure than the the static fluid around it. Check bernoullis theorum, look up vacuum ejectors or simple aircraft wing physics.
Hence a high speed train is quite capable of drawing nearby bodies towards it, as well as behind it.

HTH

 

[Tom]

Nick - if the suction effect on platforms doesn't exist, how come on St Deny's yesterday a few pieces of paper I had flew on the track after a Voyager flew past at 75mph?

 

[RJ]

Wembley Central's fast line platforms are closed off off peak for fun too!

Do you know whether the slow line platforms are closed off peak as well? I can just imagine how deafening 6K51 (Willesden Brent - Crewe) will be when coming out of Wembley Yard through there

 

[ChrisCooper]

Suction effect is definitly real, not just with trains but with any large moving object. It's strength does tend to be over-exagerated though, the ability to send lightweight bits of paper blowing around and the ability to suck a person off a platform are totally different, afterall their is a fair difference in weight. The shockwave from the front of the train passing is infact a lot stronger, but this will push anything away from the train not towards it and even then it's unlikely to be strong enough to push someone over. The effects also vary depending on the aerodynamics of the particular object, so something with a slab rear will have stronger suction than a streamlined rear (a good example is how powerful the effect from a double decker bus can be even at very low speeds by train standards). Even between similar designed trains the effects can be noticably different, a HST has less shockwave and suction than a Meridien, showing that over 30 years ago they got the aerodynamics spot on. I suppose this is likely down to a change from railway engineering (brick aerodynamics) to aeronautical engineering (highly efficient aerodynamics) to automotive (style first, engineering second).

 

[CosherB]

It's the flat back of the train that makes it worse. Imagine an 87 with a rake of mk111s as used to run on WCML. Flat fronted loco at speed will push a wave of high pressure air in front of it causing a pressure wave to anyone standing near it on the platform. Following this will be some random turbulent air behind the pressure wave and as the coaches pass. Behind the last coach is a low pressure area because the 100mph or faster airflow along the coach sides and roof cannot turn the sharp corner at the back of the last coach.

This airflow breaks away turbulently as it attempts to rush in to fill the low pressure area immediately behind the train. Trains with more streamlined rear ends (HSTs, Pendos etc) will no exhibit this effect as badly as those with a flat back (traditional coaches, freight waggons, etc).

The result as detected by someone on the platform as such a train passes at speed is first of all the pressure wave that tends to blow you away from the train, then general disturbed air, and finally the 'suction effect' as the back of the train passes - but it's not strong.

It's for the same reason that flat-backed cars (estates - which need rear wipers) and vans get filthy rear ends in wet weather whereas saloons don't. The low pressure area behind the vehicle sucks dirty road spray up from the road surface in and in from the sides.

CS

 

[westcoaster]

Do you know whether the slow line platforms are closed off peak as well? I can just imagine how deafening 6K51 (Willesden Brent - Crewe) will be when coming out of Wembley Yard through there

i should imagion there open all the time, mind you i have never seen anyone down there during the day, the down fast line platform is closed permantley apart from sundays when county stop there for what ever reason, the metro/ underground station is permantly staffed because its counted as an under ground station like new st.

iirc i believe the above train joins the main line at sudbury junction, so should be going some by wembley c

 

[RJ]

i should imagion there open all the time

Hellfire :razz:

Somebody decided to put 20313 and 37038 on 6K51 on the bloody up slow out of Wembley Yard last week, they were doing about 20mph until North Wembley then opened up big time after crossing over onto the down slow. One wonders why the signallers do stuff like that...

 

[87015]

wonders why the signallers do stuff like that...

"Playing Trains" is what its usually called!

 

[RJ]

Well some preperation is going into "playing trains" the next time the Dungy flask runs :razz: