It’s happened to all of us – you’re walking around campus, not a care in the world, and a random, strong gust of wind tousles your hair. Annoying, right? In this episode of AskNBN, Jakob Lazzaro investigates why.
Jakob Lazzaro: I’m standing in front of the Chase Bank building by the intersection of Davis, Orrington and Sherman. As you can hear, it’s pretty windy. There are a lot of places in urban environments like this – where you’ll be walking down the street and suddenly get hit in the face by a huge blast of wind. It can be pretty unpleasant.
[Aces High – Kevin MacLeod]
Jakob: I’m Jakob Lazzaro, and welcome to AskNBN. There are many places like this around Northwestern – the plaza in front of Pick-Stagier Concert Hall, Church Street in front of the Evanston public library, and the intersection of Davis, Orrington and Sherman by the Chase Bank building, to name a few. That random gust messing up your hair? You can blame those buildings. I spoke with Karen Chou, assistant chair and professor of Civil and Environmental Engineering at Northwestern, to find out more.
Karen Chou: When I was a student, so in my days, we called that the Monroe effect, which is named after Marilyn Monroe. A few years ago, there was a statue of Marilyn Monroe on Michigan Avenue, across the street from the Wrigley building. That was what the Monroe effect was, basically the wind was so great in certain parts of the Loop area that dresses basically get blown up.
Jakob: According to Chou, tall buildings interrupt the flow of wind across a landscape, creating turbulence. That turbulence forces the air around the building, including down to the street level.
Karen: If you look at water – if you put a pebble in the river, the water can go around that pebble at high speeds because you have the same volume of water. In order to move, they have to speed up because you have less area for them to travel.
Jakob: All structures affect winds this way, but Chou says a building’s shape and height are the two big factors.
Karen: If you have what we call a mushroom building, a round building, you tend to have less impact than a square building. But it will still be also at the corner of the building that you will feel the effect. Otherwise, you can feel the impact of a tall building – it doesn’t matter what shape it is compared to a short building.
Jakob: Chou says that lots of skyscrapers close together can create wind tunnels, or street canyons, because the air is forced into the only empty space – the street.
Karen: You try to spread out around a building, but then there’s the next building and you also have the wind from that trying to travel through. So now you have two of them trying to speed up in the same place. If you have a bunch of them, you can really feel the impact. So, when you go downtown, in the Loop area, you’ll definitely feel the impact on a windy day.
Jakob: So, the next time the wind steals your hat, take a look at the buildings around you.
Karen: A rock in the middle of the river – a channel. The minute you put a rock in, you create this turbulence effect around the rock, so if you happen to be by the rock, you will feel the water pushing you.
[Aces High – Kevin MacLeod]
Jakob: If you’ve got a question on life at Northwestern you want answered, send us an email – ask@northbynorthwestern.com. AskNBN and all other NBN podcasts are available on iTunes and in the Google Play store – just search North by Northwestern or AskNBN and hit subscribe to get a notification whenever we post a new episode. Our music is Aces High by Kevin MacLeod, and for NBN Audio, I’m Jakob Lazzaro.
[Aces High – Kevin MacLeod]