Question
You say there is no increase in energy? That wants explanation. I am limited in the extent of my mathematical prowess, but believe I understand the inviscid nature of "air" below the defined value of ~260 knots. First, an increase in pressure produces an immediate increase in temperature, (Boyle?), and pressure waves are present attached to any A/C travelling through air faster than 260 knots, well below Mach 1 (IAS). Consider that in the case of the Hornet flying over San Francisco Bay, it is manouvering in ground effect, which impacts the compressibility of the ambient air to begin with. Thirty feet above its position, the Pressure drop might well have been invisible. My simple understanding is this: As a mass transits an air mass, it compresses it, the air having less time to maintain its density (low) before establishing a high pressure Flow about the airframe. As the air re-enters the "hole" caused by the A/C in the air behind it, it accelerates and produces an immense release of the energy it was forced to contain during the brief transit of the A/C. This "Thunderclap" is one of two separate events precipitated by the energy of the passing A/C. "Shock" by definition means an abrupt change in "stasis" and is accompanied by all manner of fascinating phenomena, begging varying degrees of explanation, from simple to complex. This isn't a defense of my interpretation, merely my description of my understanding of a sonic event from my perspective. If you like, I will certainly admit that Pressure Differential caused that neat picture.
At my age, I'm stuck in the way I learn. I don't use Wiki, I think it diminishes the quality of an exchange. Besides, I have seen glaring errors in it, and stubbornly hold to my method of writing my interpretation, and then subjecting myself to the challenges of others, having to defend or acquiesce as necessary. Further, I don't hesitate to challenge data presented by others; I've had to eat humble pie more times than I care to count. This may be one of those times.
BRGDS, Airfoil