Singularity of Prandtl-Glauert

The singularity of Prandtl-Glauert , by whom a sudden fall of the pressure of the Air occurs, is generally accepted as causes Nuage of Condensation appearing when a Aéronef passes the Mur of the sound, but that is still discussed. It is a mathematical example of singularity in Aérodynamique.

Physical explanation

A way of interpreting this phenomenon, related to the Compressibility of the air, is to trace a wave in NR . The wave in NR is a layout of the Pression of the air according to time, seen by an observer at rest. When the compression wave occurs, the pressure observed has a characteristic layout:

  • compression causes a fast increase of the pressure (the vertical bar of the NR );
  • the rarefaction of the air near the wings makes decrease the pressure (the diagonal bar);
  • the return to atmospheric pressure restores the pressure of origin (the last vertical bar).

One can interpret the rarefaction of the air like a “rebound” of the shock wave. The clouds of condensation which one observes are sometimes observed during launchings of shuttle S, after 25 to 33 seconds, when the aircraft exceeds the zone of maximum dynamic pressure.

The phenomenon of variation of pressure being too fast to be propagated effectively, one can regard the flow as Adiabatique, and it thus implies a variation of Température. In the humid air, the fall of temperature in the zone of rarefied air - on the level of the wings, at the time of the descent - can cool the air with the lower part of sound Dewpoint: the water which it contains form then liquid goutelettes, which give this cloudy aspect. At a reasonable distance, the pressure approaches the Atmospheric pressure, which limits the extent of the phenomenon.

See too

Related articles

External bonds

  • Wilk4: To pass the wall of the sound (and vapor cones around the jets): clouds of condensation of Prandtl-Glauert, gallery;

References

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