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Re: [Phys-l] standing waves in exhaust?



Those are often termed "shock diamonds"; there's quite a good explanation here: http://www.aerospaceweb.org/question/propulsion/q0224.shtml

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________________________________
From: David Strasburger-fac <David_Strasburger@nobles.edu>
To: phys-l@carnot.physics.buffalo.edu
Sent: Wed, April 7, 2010 1:39:15 PM
Subject: [Phys-l] standing waves in exhaust?

I saw a phenomenon Sunday night that I couldn't explain; I'd appreciate
ideas and thoughts from the list.

On Sunday evening the Red Sox played their home opener against the Yankees
in Fenway. The league, in its infinite wisdom, booked the game to be
televised nationally, so instead of being played at the traditional 1pm,
it was played at 8pm.

As a result, the flyover by a pair of figher jets from the Vermont Air
National Guard was all but invisible. As they passed overhead, the most
visible feature was a luminous pink/orange cone extending perhaps one
plane-length from the aft part of each jet. Inside each cone was clearly
visible a set of bright transverse lines (6 or 8, maybe?), evenly spaced
along the length of the cone.

Any suggestions as to what might cause this?

Is it as simple as:
jet ejects wicked hot air --> wicked hot air glows --> standing wave in
exhaust (created by?) means there exist local density highs in the plume
--> higher density glowing air looks brighter than lower density glowing
air

David Strasburger
Noble & Greenough School

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