The Prandtl-Glauert Singularity - Amazing Jet Plane Shock Collar

By Gerard @presurfer
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It's an amazing site - a cone of vapor appearing around an aircraft which is travelling at transonic speed. Known as the Prandtl–Glauert Singularity this astonishing effect simultaneously widens the eyes and drops the jaw. Yet how does it occur?
(thanks Robert-John)The Presurfer