Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

I was just starting a barbecue fire by blowing on the smouldering coals when I realised I had no idea what the sound was actually caused by. I can make the sound by blowing at almost any flame I can think of, and I guess it is perhaps related to the increased oxygen consumption and a turbulent flow. Why does a disturbed flame make a sound?

share|improve this question
add comment

1 Answer 1

up vote 2 down vote accepted

The roar is indeed due to turbulence.

When a solid (or liquid) burns it isn't the solid that burns. The heat causes the solid to vaporise or emit vapour and it's the vapour that burns. When you have a steady flame the vapour burns smoothly. However, when you blow on it you make the vapour flow, and therefore the flame, turbulent. Under these circumstances the vapour burns as, in effect, a series of tiny explosions and this causes the roar.

I couldn't find a basic article on this subject (for once Wikipedia let me down), but if you Google for "flame turbulence sound" you'll find lots of scientific papers on the subject.

share|improve this answer
    
Rereading my answer this morning I realise I didn't mention that the turbulence mixes unburnt vapour with air, hence the "series of tiny explosions". –  John Rennie May 19 '12 at 6:21
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.