Talk:Prandtl-Glauert singularity
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Question: should this article have a 'see also' link over to sound barrier or is that misleading since it is an effect that is not necessarily dependent on being near the speed of sound? (though it's often mistaken for 'breaking the sound barrier'. Thoughts? jwilkinson 00:20, 7 January 2007 (UTC)
I can't tell -- do these clouds follow the plane around while Mach >=1? Or is it a phenomenon that occurs just at the moment of Mach = 1? Chrisvls 22:59, 30 Sep 2004 (UTC)
- It occures at transonic speeds, not only at Mach-1. The cloud follows the aircraft; it is not stationary. Rsduhamel 00:52, 21 December 2005 (UTC)
- As far as I know, it should occur at speeds >= mach 1, as this should follow from the underlying principles. What would change with additional speed would be the angle of the cone, becoming more acute, and if (can we presume?) the strength of the shockwave is stronger at higher speed then so should be its diameter, and if the sweep of the wing is less than this angle then the cone should have an irregular shape in the wing area. The diameter of the cone will of course be dependent upon also the local relative humidity.
- An anecdote that may be of interest. Note that the shock wave can be reflected from an underlying surface. I did not personally see this, but a fellow naval airman described a low flying supersonic overwater demonstration. He said it appeared that the aircraft was "flying inside an ice cube". -- Leonard G. 02:35, 1 Oct 2004 (UTC)
I personally observed this effect around an F-4 Phantom II that was certainly not exceeding the speed of sound. It was at the Miramar Air Show sometime in the late 1970s. It was a cool very humid day and all of the military aircraft had visible clouds in the shock waves that were forming over the wings. It seemed that the pilots were making a point of doing fast flybys to produce these clouds. The Blue Angels announcer made a point of talking about the clouds and their cause. As an F-4 flew by, with the clouds showing over his wings, for about a half second at most, a huge doughnut-shaped cloud formed around the middle of the aircraft. I cursed myself for not having my 8mm movie camera rolling. I find it very hard to believe the plane had exceeded the speed of sound since there was no sonic boom. (Actually, as I remember back, this was more than 25 years ago and the aircraft may have been an F-14 but I'm pretty sure it was an F-4.) Rsduhamel 19:19, 29 Oct 2004 (UTC)
- You all already have a link to my page where I gather information about these photos. On there is a B-2 with the effect. B-2's are subsonic aircraft. --jwilkinson 21:16, 14 May 2006 (UTC)
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[edit] Clarification Request
The wording in this article makes it seem as though the vapor starts behind the shock, i.e. the first vertical rise of the N. Pressure, and temperature, increase across a shock wave. I am pretty sure that this phenomena is created at super-critical Mach numbers (M=~0.8 - 0.9) where the flow is in a compressible regime, but the craft is not traveling at supersonic speeds. As the flow accelerates around the bulging features it accelerates to Mach one, and then beyond as it expands supersonically over the diverging features. (Think Laval nozzle, or the flow over a supercritical airfoil.) Thus there is no N wave, there is notionally half an N wave, a region of supersonic expansion (M > 1) in some cone/wedge like regions which are terminated with a shock to decelerate the flow back to the free stream velocity. It is in this sonic region that the flow is expanding, thereby dropping the temperature and pressure causing the visible condensation. The shock that terminates the sonic region then increases the temperature causes the condensation to vaporize and disappear. Also see the last two subjects "Big Mistake " and "Prandtl-Glauert Singularity"
[edit] Pictures
I really think these pictures are interesting. Keep posting more. What kind of camera can catch the Prandtl-Glauert singularity? - Fat Tony
- any normal camera or camcorder will do, though the effect can be quite short so the photographer has to be on his/her toes. See some of the videos of this effect. There are also some photographers' details of how some of these shots were taken over at my site, Wilk4: Breaking the Sound Barrier jwilkinson 00:20, 7 January 2007 (UTC)
[edit] Reliable technical information and photographic sources for the stunning Prandtl-Glauert condensation clouds
Collection of "Sound Barrier" tutorials by Dr. Mark S. Cramer. Covers the sonic boom, the sound barrier, and the Prandtl-Glauert condensation clouds. An authoritative site. Site URL: http://FluidMech.net
"Prandtl-Glauert Condensation Clouds" tutorial by Dr. Mark S. Cramer. Part of the "Sound Barrier" collection of tutorials. The site is authoritative. Site URL: http://FluidMech.net
"Gallery of Fluid Mechanics - Condensation due to the Prandtl-Glauert Singularity" by Dr. Mark S. Cramer. One of the best authenticated and documented photo collections of Prandtl-Glauert condensation clouds (alternatively, Prandtl-Glauert Singularity or Prandtl-Glauert clouds). The site really is an authority on the subject. Site URL: http://GalleryOfFluidMechanics.com
ChamorroBible.org, Tenjos (Agosto) 17, 2004, "Manguaeyayon na Palabran Si Yuus - God's Precious Words, with the Photograph of the Day". One of the best authenticated and documented photo collections of Prandtl-Glauert condensation clouds (alternatively, Prandtl-Glauert Singularity clouds or Prandtl-Glauert clouds). Eight photographs are included in Part 1 of 2 (August 17, 2004). All public domain. Site URL: http://ChamorroBible.org (generally referenced as "ChamorroBible.org" or the "Chamorro Bible" WWW site).
ChamorroBible.org, Tenjos (Agosto) 18, 2004, "Manguaeyayon na Palabran Si Yuus - God's Precious Words, with The Photograph of the Day". One of the best authenticated and documented photo collections of Prandtl-Glauert condensation clouds (alternatively, Prandtl-Glauert Singularity or Prandtl-Glauert clouds). Eight additional photos in Part 2 of 2 (August 18, 2004). Included in this collection is a remarkable NASA photo of a Prandtl-Glauert cloud around the Apollo 11 Saturn V rocket at launchtime. All public domain. Site URL: http://ChamorroBible.org (generally referenced as "ChamorroBible.org" or the "Chamorro Bible" WWW site).
--TheStudent 21:48, Dec 6, 2004 (UTC)
[edit] expand request
If anyone could give an expansive discussion on this effect and it role in fluid dynamics - compressible fluids and newtonian fluids, etc; with some weighting in the mathematics, that would be wonderful. If not, des someone have a reference they could put out. Something heavier on the math/fluid dynmaics than what is currently there. Thanks much. Ya'll are the best! 128.62.97.227 20:35, 1 September 2005 (UTC)
- see the links to Mark Cramer's explanations. jwilkinson 00:20, 7 January 2007 (UTC)
[edit] Merge
I tagged this for merger with Prandtl-Glauert method, which doesn't contain enough information to indicate whether it should really be a separate topic. From what I can tell, the "method" is simply one way of deriving the equation of the singularity. If I'm wrong here, then that article certainly needs expansion. --Dhartung | Talk 07:19, 15 June 2007 (UTC)
- I don't know much about the topic, but from what I ascertained I agree. RideABicycle | Talk | 23:28, 5 August 2007 (UTC)
[edit] Prandtl-Glauert singularity
The phenomenon is not necessarily airspeed related; it occurs when there is a change in air pressure. According to Bernoulli's principle, the airflow across the top of the wing is faster than that across the bottom because the wings are cambered, and the airflow over the top has further to travel in the same amount of time. This creates a high pressure beneath the wing, and low pressure on top. The two pressure areas attempt to swap, which is what creates wingtip vortices. Increasing the airflow (with airspeed, for example) will increase the difference between the high and low pressure areas, which creates lift. As the Prandtl-Glauert Singularity suggests, the drop in air pressure can drop the air temperature below the dew point, which causes visible moisture.
While Prandtl-Glauert Singularity seems to be specific to airspeed related visible moisture, there there is another way to create this effect -- an effect fighter pilots refer to as "vapes." It usually occurs in humid air during high-G maneuvering. We've all seen this airshows before; it forms on the wings and leading edge extensions of aircraft like the F-16 and F-18.
[edit] Big mistake
Gentlemen, I think there is a big mistake here. What you call the Prandtl-Glauert singularity,is not what is really happening to the airplane. Prandtl and Glauert did not work together. There is a rule that have their names, but they work on it separatedly. It is based on potential flow, small disturbances, and it is used to correct the perfect flow around a body due to compressibility. But, instead of that, Prandtl worked with Theodor Meyer 8one of his students) to modelize shock and expansion waves. What we are viewing in this photographs is that. expansion flow, with Mach waves (sound waves). The aircraft is flying subsonic, but it has a Mach number greater that the critical one. Then there is supersonic flow over the airplane. For those parts were an expansion (cockpit, tail before the local shock)occurs the humidity of the air is condensed. You can find an introduction on this subject in "Foundations of aerodynamics" Kuethe-Chow. Hope this helps. [Carlos Gayer]190.48.115.60 06:35, 6 October 2007 (UTC)
- Thank you, I believe that the "Prandtl-Glauert-singularity-clowd" is more like an urban myth. So far nobody could explain, where the singularity is. Neither a shock wave nor a steady pressure drop into a condensation condition describes a singularity. There must be an error here. Is there anybody with a good aerodynmics textbook who can explain? 88.217.24.161 (talk) 19:44, 18 December 2007 (UTC)
[edit] U.S. Flag Picture
In a science article like this, in a politically neutral encyclopedia, the U.S. flag shouldn't be on the foreground starring the picture. Please change or modify the picture. Thank you very much. --158.42.244.159 (talk) 18:58, 13 May 2008 (UTC)
