Ok, this might not be so much GA, but I’m sure one of you guys will be able to enlighten me.
Why do jets with afterburners have a visible pulse in the afterburner flame? I was under the (probably mistaking) belief that combustion in jet engines was a continuous process, with different parts of the engine at different stages of the cycle.
Here are examples of that I’m asking about
…belief that combustion in jet engines …
Your belief is correct as far as it concerns the “in” bit in your sentence. But the images show what’s happening out side the jet engine where the supersonic exhaust is slowed down to a stationary atmospheric state. As usual, Wikipedia already knows all about it: http://en.wikipedia.org/wiki/Shock_diamond
As said in the post above.
You can see the areas of pressure changes in the air/gas flow due to the flame, something that you can’t see in the air intake. Engines in a supersonic aircraft can’t breath air at supersonic speed so the airspeed must be reduced to subsonic, this is done inside the air intake. Search for a photo of the Dassault Mirage, at the intakes you will see something that looks like a triangular piece pointing forward (we used to call them mice). Their purpose is to created a shock wave at the entrance to the air intake. Every shock wave causes a drop in speed, hence an increase in pressure, usually there will be more than one shock wave created inside the air intake so by the time the airflow reaches the engine’s compressor the air flow is subsonic. So, not being very scientifically correct this is what you see in the photos that you provided but at the back side of the engine.
Hope that this helps.
Thanks guys! Really appreciated, and easy to understand 
With the SR-71 it’s just the amount of awesomeness that determines what comes out of the pipe.
I would settle for something quite boring really… don’t mind if the exhaust doesn’ t have any pretty patterns because nobody is going to be seeing it for very long
