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Candle Behind a Flat Plate

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Watch the video on YouTube.

What kind of experiment is this?

Experimental procedure and explanation:

  • When you place a candle behind a flat plate and blow from the front of the plate, the flame of the candle is not blown out.
  • This is because the flow is blocked by the plate and does not wrap around to the back. This phenomenon in which the flow separates from the object in this manner is referred to as “separation.” Around many objects, the flow is separated, but a separated flow does not form easily when the object has a streamlined form. (Reference: Dolphin Jump).
  • When the plate is relatively small, as shown in the figure on the right, a weak flow that circulates behind the plate can be generated. Such flow is referred to as a “separation vortex.” From the video of the experiment, you can see that when the person blows on the plate, the flame of the candle placed behind the plate bends forward. This is due to a separation vortex. If you blow vigorously on the plate, you can even blow out the flame of the candle due to this separation vortex.
[Keywords] separation vortex, ring vortex
[Related items] Blowing Out a Candle Behind a Cylinder
[Reference] “The Wonders of Flow,” Japan Society of Mechanical Engineering, Kodansha Blue Backs, pp.136-139
“Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natume Publishing, pp.68-69


Last Update:1.21.2015