Three mechanisms that cause gusts at subway stations
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At subway stations, strong winds may blow on the premises, and in London Underground, strollers carrying children may be caught in the wind and fall into the track . This wind was created from pressure differences and multiple mechanisms.
Why Are Metro Stations So Windy?-The Atlantic
https://www.theatlantic.com/science/archive/2019/05/why-are-metro-stations-so-windy/590686/
Julie Bogen, a reporter on the news site The Atlantic, encounters a flurry when using the subway in Washington, DC. We asked Professor Kenny Brewer of the University of Brown's engineering department why such a thing happened, and got an answer that 'The gust of the subway is created by the pressure difference and the three mechanisms related to this.'
◆ 1: Piston effect
One of the mechanisms presented by Professor Brewer is the ' piston effect '. This refers to the change in air pressure that occurs when an object moves in a narrow place such as a tunnel.
As the train travels at high speed in the subway tunnel, the air in front of the train is compressed and the air pressure rises, and conversely, the pressure in the back is reduced and the air pressure decreases. Therefore, when the train passes through the tunnel and enters the home, the air pushed by the train is discharged to the home and the air in the home flows into the tunnel. There are multiple homes in an actual subway yard, and trains moving in different directions move into and out of one space, which causes 'incredibly complex pressure changes'.
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◆ 2: Bernoulli's theorem
Another mechanism suggested by Brewer is 'The Bernoulli's Theorem .' 'The Bernoulli's Theorem' is an equation representing the conservation law of energy related to fluid, and according to this theorem, the law is derived that 'if the pressure is high, the speed of the wind will be slow, and if the pressure is low, the speed will be faster' You A closed underground space is prone to changes in air pressure between large spaces and small spaces, which makes the air flow irregularly, so it is easy to create a place where the wind flow is local. 'It has become an environment.
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◆ 3: Thermodynamics
'Thermodynamics' is the third mechanism that generates the pressure difference in the subway. This is a phenomenon that can be seen not only in the subway but anywhere on the earth, but warm air expands and the specific gravity gets lighter, and as a result it rises. Conversely, cold air descends because of its high specific gravity. Due to the temperature difference between the underground and the ground and the air conditioning in the subway, cold air may flow into the subway and air may flow out of the subway, which may be the cause of pressure change and air flow. Professor Brewer explains.
by Henning Klokkerasen
Borgen asked the Washington Metropolitan Area Transportation Bureau for further investigation, but he did not get back it, 'Commuters still challenge the subway today, my hairstyle is ruined, someone The skirt will come back, 'he concluded.
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