Tuesday, September 20, 2005


Prandtl-Glauert Singularity

"Spanky" sent me some good pictures of aircraft "just below", or "breaking" the "Sound Barrier". Though the condensation cloud forms quite often when an aircraft goes faster than the speed of sound, the "cloud" can also occur at sub-sonic speeds in level flight. This is due in both cases to the Prandtl-Glauert Singularity. Near Mach 1, the Prandtl-Glauert singularity has amplified all pressure perturbations. As a result, the regions of expansion ( low pressure ) above the wings and cockpit correspond to much lower pressures than we would expect in an incompressible flow. As in other condensation problems, the lowered bulk pressure results in a lowering of the temperature causing condensation of the ambient water vapor.

Condensation caused by the Prandtl-Glauert Singularity can be seen in steady level flight usually at low altitude under humid conditions. This contrasts with the situations associated with lift and vortex generated condensation where large accelerations (due to maneuvers) are required.

On humid, very warm mornings, this can also be witnessed, to a degree, from the propellers on our floatplanes as they take off, due to the speed of the propeller tips during the take-off phase when the aircraft is under full power and RPM. Condensation is formed at the end of the blades, and is then sucked into the slipstream, and can make quite a visual spectacle.

Anyhow, check out the pictures, they are quite intriguing.

Nice photo of the B1-B "Lancer"........ Posted by Picasa

F-14 "Tomcat"....... Posted by Picasa

A Navy "Blue Angels" F-18 "Hornet"......... Posted by Picasa

F-18s........Cool! Just like the the "Starship Enterprise", going through the "Space/Time Continuum".......... Posted by Picasa

F-18 "Super Hornet"....... Posted by Picasa

Another F-18...... Posted by Picasa

So, there you have the photos Spanky sent me. Then, I did a little research to show you the condensation cloud can occur before becoming supersonic. Check this out!

B-2 "Spirit" Stealth Bomber........... Posted by Picasa

The B-2 is a sub-sonic aircraft, so this shows that the condensation cloud is not an indication of breaking the sound barrier, although a large percentage of the time a cloud "can" occur when becoming supersonic.

Check out my "Video Of The Day" tomorrow, and see the Prandtl-Glauert Singularity for yourself!

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