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Blowing Out a Candle Behind a Cylinder

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What kind of experiment is this?

Experimental procedure and explanation:

  • When a candle is placed behind a round PET bottle, and you blow on the bottle from the front, the flame of the candle is blown out.
  • From this, we know that when a flow is applied to a cylinder, the flow wraps around to the back of the cylinder.
  • However, it is important that the flow is a “jet” flow. A jet is a flow from a pipe or a hole. When a flow is such a type of narrowed flow (jet), the flow easily wraps around a round object, along the surface of the object. This is known as the Coanda effect. In contrast, when ordinary wind or other such flows are applied to an entire space (i.e., uniform flow), not much of the flow can wrap around to the back.
  • Even when you blow on the cylinder from a position that is slightly off center, the flow bends along the cylinder, and the flame of the candle is blown out.
[Keywords] Coanda effect
[Related items] Candle Behind a Flat Plate
[Reference] “The Wonders of Flow,” Japan Society of Mechanical Engineering, Kodansha Blue Backs, pp.128-133 and 140-143
Last update: 1.21.2015