Shock Wave Formation in Transonic Flight
Why Aviation Stack Exchange recommends it
Aviation Stack Exchange answerers link it as a real-world picture of transonic flow and a normal shock when explaining critical Mach number.
Recommended by 1 people across 1 different months, 2017 to 2020.
What it is
A 45-second clip filmed from a passenger seat showing a shock wave forming above the wing of a Boeing 737 in cruise. The description explains that the aircraft is near Mach 0.8, so airflow over part of the wing is supersonic, and the shock is visible through optical distortion and a shadow on the wing.
What people said
Recommends Peter Schilling · 2017-12 · Aviation Stack Exchange · on “Is there any aircraft that cruises in the transonic regime?”
If we define the critical Mach number [LINK] as "the lowest Mach number at which the airflow over some point of the aircraft reaches the speed of sound, but does not exceed it," then yes, many aircraft cruise above this speed. Any modern jet airliner has some supersonic flow over parts of the wing and fuselage at cruise, placing it squarely in the transonic range. This video [this video] and its description provide a great visualization and explanation of the associated phenomena. It should be noted, however, that there is not necessarily a large increase in drag upon reaching the critical Mach number. More useful in the transonic range is the drag-divergence Mach number [LINK] , which is always
Cites Fiddlesticks · 2020-02 · Aviation Stack Exchange · on “Cruise Mach Number less or more than Critical Mach Number”
@GdD critical mach is the lowest airspeed at which the airflow reaches Mach 1 over **some** part of the airframe. That does not necessarily mean departure from controlled flight. In this video [LINK] you can clearly see the normal shock wave dancing back and forth across the wing as an A320 exceeds critical mach in cruise flight. And on a 737 [this video] . And on a 757 [LINK] .
Cites Darjan · 2020-04 · Aviation Stack Exchange · on “Cruise Mach Number less or more than Critical Mach Number”
The critical Mach number $M_{crit}$ is defined as the lowest Mach number at which the airflow over some point over the airfoil reaches supersonic speed, that is, Mach 1. Usually, flying greater than $M_{crit}$ will produce a normal shockwave perpendicular to the flow, at the point of minimum pressure on the airfoil. I must note that if flying slightly above $M_{crit}$ , there is a possibility of the isentropic recompression of the fluid, which means that no shockwave will be formed and thus no losses in form of the entropy will occur. This is especially the case with supercritical airfoils flying slightly above $M_{crit}$ . Critical Mach number for a typical transonic airliner is not equal t