I've had time to think about this, and below I give my latest thoughts. I had hoped one of the real experts would have definitive data to answer these points, and I still hope someone will check this out for you.
Shock Waves
Shock waves are a thin surface in the airflow where there is a sudden fall in true airspeed and a sudden rise in static pressure behind the shockwave. These two effects lead to a sudden rise in air temperature and density also rises as the effect of the increased pressure overcomes the effect of increased temperature.
In an adiabatic change, as this is, total energy in the airflow remains constant, but now, post Bernoulli, some of the energy is thermal, so it is no longer true that static pressure energy plus dynamic pressure energy equals total energy. The thermal energy – the high temperature air – is lost downstream. Lost energy means drag, and this is wave drag, always present when shockwaves form.
Shockwaves can be normal to the airflow - at 90º to the flow - or oblique. Normal shockwaves bring the airspeed down to subsonic values, which is a big jump, so the pressure and temperature rises are large, as is the energy loss. The higher the freestream speed ahead of the normal shockwave, the greater the effects, so minimum energy is lost in a normal shockwave that forms in airflow just at or just above M1.0.
Oblique shockwaves at angles of less than about 70º to the flow only bring the flow down to a lower value that is still supersonic. For any given freestream speed oblique shockwaves are less intense than normal shockwaves, pressure and temperature rises are smaller and less thermal energy is lost.
Expansion waves are diffuse areas where supersonic flow is accelerated. Through an expansion wave airspeed and pressure fall, and so do density and temperature.
Ambient static pressure is constant, unless the aircraft is climbing or descending. This is not the same as static pressure in the airflow, which goes up through a shockwave and down through an expansion wave.
Q. What happens to total energy? A. Remains constant all the time.
Q. Static pressure? A. Up through a shockwave, down through an expansion wave.
Q. Air Temperature? A. Up through a shockwave, down through an expansion wave.
Q. Total head pressure? A. Down through a shockwave, up through an expansion wave. Note that total head pressure is not total energy because of the missing thermal energy.
Q. Least energy loss? A. Shockwave at just over M1.0 freestream. Has to be a normal shockwave as you can’t get oblique shockwaves at this Mach number.
This makes the answer B, as the higher temperature energy in the normal shock means a lower pressure energy if the total is to remain the same.
Any comment, experts all?
Dick W