Forum: Technology

I've seen a little movie where a jet breaks the soundbarrier, it creates a hughe cloud, what's the cause of this cloud forming? It's weird, you can even see the cloud bending when it's formed in front of the jet's nose just before the jet's inside the cloud.
Here's an example of what I mean

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its when the water vapers evaporate once it crosses the sound barrier its hard to do the moisture in the air, attude, speed has to be right

I have no idea what the above post is trying to say. It simply an extreme example of the Doppler effect. The sound waves which travel at a fixed velocity (~345m/s) are compressed in front of the aircraft as it approaches the speed of sound. Thus, sound waves (think of it as air molecules) are compressed into a very small volume with high energy density. This is often called a shock wave and the high energy density waves will spread away from the source of the sound in a V-shape, just like a motorboat moving through water (in this case, the source -boat- moving faster than the waves in the water, results in a bow shock). Also, not appearant in this clip is the sonic boom, when the shock wave crosses the observer, there is a sudden pressure pulse that reaches the ear (like a lound bang).
Pat

Thanks Pat, that was very useful.
Also thanks to the other guest for trying to give me an answer.

Great explanation and a great pic Wink

of F-15i

In my best Homer Simpson: MMMMmmmm....shockwave... Smile

c'mon you guys!

It's the expansion of the water vapor coming outta the shockwave or at least a compressed region of air.

As the air expands, the water vapor becomes visible due to the drop in temperature. Air expands, air cools, vapor becomes visible. Heard of 'dew point'? Think that cloud base might be at the 'dew point' temperature?

later, making the chilli for the game......

Gums is close - what you are seeing is any humidity in the air coming out of solution as it enters the region of lower pressure behind the shock wave boundary. This low pressure area isn't very big and as soon as the pressure rises the vapor goes back into solution. The temperature drop Gums mentions also occurs when the pressure drops. It is closely associated with the "dew point" which is a function of humidity, pressure and temperature. This is why the "cloud" is more easily visible during high humidity conditions.

This effect is the same phenomenon that results in visible wingtip vortices and those strake vortices the Viper is so famous for. You don't have to be going supersonic for this to occur but, in the examples in this thread, the pressure drop across a shock wave produce the same effect. This (explanation) is what happens when you take too many Thermodynamics courses - your (my) head fills up with geeky facts... Embarassed

Gums, what game??? Wink

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Gums wrote:

c'mon you guys!

It's the expansion of the water vapor coming outta the shockwave or at least a compressed region of air.

As the air expands, the water vapor becomes visible due to the drop in temperature. Air expands, air cools, vapor becomes visible. Heard of 'dew point'? Think that cloud base might be at the 'dew point' temperature?

later, making the chilli for the game......

Same thing happens inside of an altitude chamber during rapid decompression. Been in one and saw that, neat phenomenon.

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JR

Fly Fast, Zipper Fast

Haha, I know I know - I razz my buddy here all the time by asking him "who's playing?" Wink

We watched the game at the local Hooters last night... Shocked

You guy's crack me up!

Forum: Technology

Cloud when breaking soundbarrier