IIRC the definition of HE is that the detonation front propagates faster than sound *in the unshocked material*. What happens in the air depends on how far away you are.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Issac Newton
You missed the point. They use air-breathing engines so there are super-sonic shock-fronts in the combustion path.
-- Bill Sloman, Sydney
No there aren't. A jet turbine is designed to specifically avoid that. The speed of sound goes up with both heat an pressure - it never goes supersonic in the engine.
You missed the point because:
You're wrong, asshole:
"... airflow in a scramjet is supersonic throughout the entire engine."
Where are these scramjets used, Bill?
Sorry - I meant Fred.
David is incorrect. Only temperature. Pressure has nothing to do with it until you reach non-ideal gas behaviour (trans-sonic conditions).
The speed of sound is directly connected to the speed of individual molecules. The temperature is a measure of the average kinetic energy of those molecules bouncing off a boundary. Kinetic energy is proportional to m*v^2; so v changes as sqrt(temp) (times a multiplier that depends on the molecular mass and geometry).
For sea-level air, the speed of sound in m/s is almost exactly
20*sqrt(k) - where k is in degrees Kelvin.Bill, this is completely wrong. Any expulsion away from the direction of travel imparts momentum.
As the space shuttle main engine approaches orbital velocity, its exhaust is still travelling forwards at a significant multiplier. A rocket is most efficient when the exhaust is stationary, because it carries no waste kinetic energy (except you obviously can't launch like that!)
Given the relatively fixed temperature limits of nozzle materials, a rocket engine for low-speed flight needs an exhaust gas with a high molecular mass and a low speed of sound (like the semi-burnt rubber of the solid fuel boosters). For high-speed flight, you want a low molecular mass and consequent high exhaust velocity - like H2O. Exactly why the shuttle has solid fuel boosters for low-speed climb and H/LOX engines for orbital insertion.
Clifford Heath.
A followup to this. The peak temperature in the shuttle main engine is around 6000F, or 3588K. The speed of sound in steam at 100C is about
477.5m/s. Therefore the flow velocity in the nozzle constriction (0.26m diameter) of the shuttle main engine (which is the local speed of sound) is about 477.7*sqrt(3588/373) or 1481m/s, around (air) Mach 4.33. This is calculated according to the ideal gas law. Non-ideal behaviour increases the speed of sound. Of course, there's always expansion after the throat too. So at full power, the exhaust can in theory surpass minimum orbital velocity of 6900m/s (after expansion to 4.6 times the nozzle throat velocity).In any case, the question is moot. It doesn't have to surpass the shuttle's velocity to impart momentum.
So, only in research. Not in practical applications.
Proven engineering developmental models is beyond research. Applications are limited to ultra high speed, and thus ultra high altitudes. The technology is ready, the drawback is absence of commercial market.
So, only in research. Not in practical applications.
So, not in practical applications. Even the SR-71 (Mach 3) did not use the Scramjet. Do you know why?
On Sun, 16 Aug 2015 10:32:37 -0500, John S Gave us:
Scramjets and ramjets only work after the airflow rate is above 500 mph already.
So, they'll see use in hypersonic applications..
They have no moving parts inside. So there is nothing for supersonic effects to do damage to.
On Sun, 16 Aug 2015 12:41:18 -0500, John S Gave us: snip
Consumption rate. And it does not function under 500 mph.
And that tech then was RAMjets, not scramjets.
There's a big difference between the speed of sound in -40C air and in
4000 C jet exhaust, so the hot exhaust can be subsonic (at 4000 C) while propelling the plane supersonic (at -40C). (According to an old NASA paper I found, with afterburners on, jet exhaust gets up to almost 3800 Reaumur (4750 C).)The SR-71 engine was mostly subsonic, which was part of the point of having the spikes coming out of the middle of the intakes--they slowed and so compressed the intake air.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
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It has to leave the engine going backwards faster than the plane is going f orwards (by conservation of momentum). If the plane is travelling forward f aster than the speed of sound, the the exhaust gases have to leave the engi ne traveling at super-sonic speed relative to the engine.
There's a supersonic shock in there somewhere.
Do me a favour and learn to do joined up logic. You contradicted yourself w ithout noticing that you'd done it.
-- Bill Sloman, Sydney
There was no mention of scramjets at all just un-contained fuel air and the idot introduction of jet turbines which are irrelevant to the discussion as are scram jets
The engine is traveling supersonically (at standard temperature and pressure) NOT the air - the air while going through the engine also never goes super sonic due to increases in the speed of sound due to increased temperature and pressure.
No there is not and that is by conservation of momentum. Stationary air with mass is accelerated to causes thrust which causes a reaction equal and opposite. It doesn't matter what speed the engine is already moving at
Really? Lets see about the must be faster exhaust thingy shall we. A rocket can travel at 25,000 miles per hour are you going to say that the rocket exhaust must be faster than that?
The subject was un contained fuel air explosions. You just through in a red herring to make yourself sound important and you were also wrong.
v = 331 m/s + (0.6 m/s/C)*T (where T is temperature in degrees Celcius)
Seems unlikely to be true.
The speed of sound doesn't change much with temperature, and less with pressure.
-- Bill Sloman, Sydney
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