I think maybe I remember reading something about aircraft, that when they accelerate through a Mach number of 1 there is a sudden changing of various parameters and stresses and whatnot (this part seems clear and well documented), and again when going through Mach 2, and Mach 3, and so forth, with special things happening in the immediate vicinity of integer values of the Mach number. It’s these special behaviors around integers 2 and above that I am asking about.
I ask because I am simulating air flows through holes, and it’s special right around Mach 1, but not obviously so right around Mach 2. So maybe I imagined that bit about 2 and above? On the other hand, I’m having some difficulty getting the simulations to go above Mach 2.17, so maybe this is the problem after all? But then people tell me simulation is more difficult when supersonic.
So, is Mach 2 special? And higher integers? Or did I make that part up in my head?
It is my understanding that there are actual physical properties like drag and vibrations from air passing over wings that cause issues when approaching mach 1. I don’t think those issues exist as a barrier for mach 2 or 3. Mach 2 or 3 are just 2x or 3x mach 1.
Transonic flight is indeed where interesting things happen:
Once you are fully supersonic, nothing much more interesting happens. Looking at plots of drag versus Mach number, drag, temperature and pressure all continue increasing, but there don’t appear to be any distinct transition speeds where discontinuous changes occur.
The next region is hypersonic from Mach 5 to 10. Entropy and thermodynamics play a large role in airflow in this region but there is not a discontinuity as the speed increases like there is at Mach 1.
Mach 1 is a violent region for subsonic aircraft. I believe it was Chuck Yeager who determined that some of the controls actually reversed in transonic flight.
Ha! I saw that movie. The last imaginary vestiges of the British empire. As Yeager said about the movie it was fun but if anybody reversed the controls while going transonic, they’d be dead.
The problems with going through the sound barrier don’t all just happen at the speed of sound.
What happens at the point of hitting the speed of sound is the sonic boom.
But various effects occur in the speeds NEAR the speed of sound, because some of the air around the plane hits its speed of sound…
speed at which the plane stalls.
speed at which control surface greatly loses its control .
speed at which the wing flexes so much as a response to a control surface that the controls effect is reversed…
4 interaction of shock waves between wing and tail causing various effects like 1 -3 but at the tail.
wing flutter causing instability.
They are all different speeds if the plane has the problem at all …and a different speed for each design.
But they are all near the speed of sound and there aren’t similarly linked speeds for any problems of higher speeds.
I have already found new and interesting phenomena for my air flow simulations through a hole. There are Mach diamonds, and shock fronts with apparent discontinuities at various orders, and huge adiabatic temperature changes. Whatever else, this work has been fun and interesting.
The sonic boom happens continually, for as long as you’re going at any speed greater than sound, just like the wake of a boat happens continually (they’re very similar phenomena, just with different kinds of waves).
Yes, you start having a continuous sonic boom, from the vehicle’s point of view, but it’s momentary from the point of view of somebody on the ground. This is one of the “shock fronts with apparent discontinuities” I referred to.