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Old 8th Jul 2008, 01:31   #1 (permalink)
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Allison 250-C20

A question for all the techs & mechs....

I am trying to get my head around the toroidal vortex in the can of the jetty engine.

My understanding of a toroidal vortex basically a 'donut' spinning in on itself
(Vortex Ring State being a good example of a toroidal vortex).

So my question is how does the air actually flow within the can, to form this 'cooling buffer' (from what I have read large % of air is actually used for cooling).

I am assuming that toroidal vortex spins outwards with the flame, then back up behind the lining. is this correct?

any tips for novices greatly appreciated
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Old 9th Jul 2008, 04:03   #2 (permalink)
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Tool benders

Hey Gadget, did you also post this on the engineering pages?
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Old 9th Jul 2008, 11:34   #3 (permalink)
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Basically (very basically) the toroidal vortex is the air that is not used of for combustion - it is designed to swirl around the outer edge of the combustion chamber to keep the flame path away from the combustion liner.

If the toroidal vortex flow is disturbed (blocked or damaged guide vanes etc) then the flame path can touch the combustion liner and eventually burn through.

I seem to remember the Rolls Royce Engine book has some decent diagrams of the airflow in the combustion zone.
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Old 9th Jul 2008, 14:58   #4 (permalink)
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The allison 250 uses more of a swirl (similar to the airflow produced by a propeller) than a toroidal vortex. Actually it uses two of them in opposite directions

If you click on this link and scroll down to the third set of pictures you will see an Allison 250 combustion liner with a very basic explanation of the swirl.
The combustion chamber

Then inner ring of baffles (pressed flat flaps in the right hand picture) blow air in a counter clockwise (as you look at it) direction and the outer ring blows in a clockwise direction. This swirling primary air causes good mixing with the fuel for burning, it also shapes the flame and with the help of the secondary airflow, keeps it central in the chamber. 25% of airflow is used in the primary area (the holes on top in the left hand picture) 72% passes through the holes around the outside of the liner for cooling and to keep the flame away from the walls of the liner and the final 3% passes along the outside
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Old 9th Jul 2008, 23:03   #5 (permalink)
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And if you look at the sixth set of pictures, Fig 3-13 (b) it will show you how the toroidal vortex is formed.
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Old 9th Jul 2008, 23:55   #6 (permalink)
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opposing airflow

many thanks for the link & info

from the diags there it appears i had assumed the complete opposite direction of flow for the toroidal vortex...(& we all know what ass.u.me does)

image credits to Mr Roger Marmion

so i was thinking that the flame at center of can to keep at most distance from can lining, airflow of flame would create too strong a force for the toroidal vortex to flow in opposite direction. Just as the high & low pressure systems will rotate in opposite directions allowing more fluid motion, my assumption that if strongest flow of (flame) air being pushed through the turbine that (logically) the inner part of torodial vortex would spin with the flame not against it as indicated at (b), very intriguing that it goes against the flow of the flame.

either way a pain to animate.
many thanks to those who posted,
send me a PM if you'd like a peek at what I've done so far

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Old 10th Jul 2008, 00:15   #7 (permalink)
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Against the flow of the flame?????
Looks pretty much like the pattern of the nozzle to me.

Remember that its mostly pressure at this position not velocity.
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