What is the velocity of Hypersonic and what is it’s significance?
I don’t think there is a strict definition. In aviation, “supersonic” is usually used for speeds faster than sound but still attainable with conventional jet engines. Hypersonic is anything that requires rocket engines or more exotic jet engines, above Mach 4 or 5 I think.
A hypersonic airliner would be able to do a NY to Tokyo flight in about an hour. More significantly, a hypersonic aircraft may be able to reach orbital speed (about Mach 24), requiring only a small rocket engine to push it all the way to orbit. This would be more efficient than conventional rockets because jet engines use oxygen in the air, instead of oxygen (or oxydizer) stored in big tanks. The hope is that we’ll be able to build a completely reusable spacecraft this way, dramatically reducing launch cost.
I deal in low-speed fluid flows myself, but I believe hypersonic flows are those in which dissociation of the gas becomes a factor. It’s not really a hard-and-fast speed (or Mach number) - it depends on lots of things. Something like a re-entering space shuttle deals with Mach numbers of something like 11 in the upper atmosphere, which is well into the hypersonic regime.
The basic idea is that a body moving supersonically will create a shock (an abrupt discontinuity in fluid velocity, pressure, and temperature) in front of it. The strength of the shock will decrease with distance from the object (winding up as a “sonic boom” far off), but near the body it can be quite strong. Pressures and temperatures increase drastically behind the shock - going up from what they are out in the freestream.
If the speed (OK, Mach number) of the moving body is sufficiently high, the pressures and temperatures behind the shock can be enough to cause gas chemistry to be a factor - dissociations and reactions will actually change the composition of the gas. Different gases means different fluid properties, and these changes in cannot be ignored if one wants to accurately predict the behavior of flow. For this reason, the regime in which they become important gets its own special name - “hypersonic”.
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Subsonic flow – Mach numbers below 0.8
Transonic flow – Mach numbers from 0.8 to 1.20
Supersonic flow – Mach numbers from 1.20 to 5.00
Hypersonic flow – mach numbers above 5.00
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http://www.farnborough-aircraft.com/Theory_of_Flight/High-Speed_Flight.asp
The site also has some good diagrams and explanations.
It’s also a rollercoaster at Paramount’s Kings Dominion, that launches riders 0-80 in 1.8 seconds, up a 90 degree hill, down 90 degrees on the other side, and then around, over a bunny hop and back to the station. It’s “Hypersonic XLC.” Its significance is that it is the first air launched roller coaster, and it has the fastest acceleration of any thrill ride in existance. As far as the term ‘hypersonic’ goes…that’s been explained!
Jman
I read in an old National Geographic that Hypersonic designates the velocity a ramjet airplane must fly to achieve full supersonic airflow WITHIN the ramjet engine.
At this airflow velocity, the only fuel that can combust is hydrogen or a hydrogen/methane mix.
Bibliophage is right, hypersonic is just flow faster than mach 5(from my compressible fluid flow textbook). What you are thinking of, enolancooper, is called a scramjet(Supersonic Combustion RAMJET). Mmy understanding is that they are designed to operate at hypersonic speeds, but the definition of hypersonic isn’t based on the threshhold at which combustion occurs at supersonic speeds.
After dusting off my old Aerodynamics text, I’d concur with the Mach 5 convention for “hypersonic”. (I don’t use this section much, being a helicopter guy). The explanation for this number has to do with the notion of certain linearizing approximations that don’t work well above Mach 5.
Side note- ever notice that low speed airplanes have sort of a blunt-nose look to them? That’s because at speeds under, say 200 knots the effects of compressibility just aren’t important. Take a look at supersonic airplanes (F-104 is the best example). You get needle-nosed airplanes that look fast even when they’re just sitting still. The reason is to deal with the transonic/supersonic flow. Then, take a look at the Space Shuttle (which has to deal with, what, Mach 15 or 20?) and you’re back to a blunt-nose look again. Why? Heating at those hypersonic speeds would just melt a sharp nose, it has to be blunt to survive. As for drag, who cares, the trouble is in getting the thing to slow down!
Just an observation.
uh…just to kinda sum up all the other posts in this thread: the definition of hypersonic is: REALLY DAMN FAST!
So Hypersonic is Mach 5+. Thanks.
PS…
“Hypersonic XLC.” isn’t the fastest acceleration of any thrill ride. In Australia they have a huge L shaped tower…
::The Tower of Terror::
600 tonnes of steel
2.2 megawatts of power
160 kph
4.5Gs
38 storeys
The ride is propelled by electro-magnetic forces.
The whole ride is over in about 12sec.
PSS…
Doesn’t the SR-71 use SCRAMJETS? That’s the purpose of it’s coned shaped intakes, provides about 71% of it’s power.
PerfectDark
I stand corrected, apparently there is a strict definition for hypersonic (>Mach 5).
The SR-71 does not use a scramjet engine. In a scramjet engine, the flow of air through the engine remains supersonic. In conventional engines, the air is slowed down to subsonic speeds by the inlet before it is mixed with fuel and burnt.
Nobody has flown a scramjet-powered aircraft yet. The NASA Hyper-X program will be the first to do so, albeit with an unmanned expendable test vehicle. This will happen later this year, if all goes well.