Question about the sound barrier

[Angleochoas]

Has any aircraft that is capable of breaking the sound barrier, ever been fitted with equipment to test possible variable introduction?
IE; Amplification, dispersement, manipulation of result?

Aircraft can refer to any type of projectile, manned/unmanned.

 

[RainmanTime]

Has any aircraft that is capable of breaking the sound barrier, ever been fitted with equipment to test possible variable introduction?
IE; Amplification, dispersement, manipulation of result?

Perhaps if you clarify what you are asking, I could provide an answer. What do you mean by "variable introduction"? What do you mean by "manipulation of result"?

Can you be more specific as to what you are asking? Thanks,
RMT

 

[Darby]

Angelo,

Are you refering to EM induction experiments that use magnetohydromagnetics (MHD) to accelerate to > Mach 1 without a sonic boom?

If so, then yes. Experiments have been done. Ray is a lot better than I am in this field. It's what he does for a living. But you can Google "magnetohydrodynamics" and look at the articles.

The short answer is that in theory a plasma field can be used to propel an aircraft by surrounding it with the plasma. DOing this can seriously reduce or eliminate the sonic boom by basically layering the airflow so that the relative velocity of adjacent layers across the gradient never exceed Mach 1.

It's a big step from theory to applied science and then to design engineering. But the science appears to be solid at the theoretical level.

BTW: Though its not MHD, high by-pass turbofan jet engines use the same general physics to quiet the engine noise. The airflow through the engine is layered so that adjacent flows don't have supersonic relative velocities...it eliminates the high frequency "scream" that you hear in high performance jet fighters. You've probably heard modern commercial jet engines - they hum instead of scream.

 

[Darby]

Angelo,

Again, Ray will be much better at the details of this, but one really big issue with layering the airflow with the plasma involves the flying surfaces themselves. Sure, you might reduce the noise but will the puppy actually fly and if so, will the flight be stable? If you do any radical maneuvers the orientation of the EM field will lag behind the aircraft and it will also twist as the aircraft changes its orientation. How to mainitain controlled flight is one of those applied science-design engineering issues that go far beyond the theoretical science. Quietly going supersonic to only end up as a large hole on the surface of the Mojave Desert probably isn't very helpful. And "punching out" of the aircraft through the plasma if the pilot loses control won't be much fun either.

 

[Angleochoas]

Forgive my terminology etiquette Ray,

Darby gave some interesting reads there. Thanks for that.
Basically was bored and looking at visuals of aircraft attaining sound barrier speeds and wondered if any theoretical testing had been done in terms of the actual effect - breaking the sound barrier achieves (sonic boom); such as Darby noted.
Interesting stuff for sure.
One thing I'm curious about and it may sound like a dumb question, but even on a finite level, does the 'sonic boom' affect acceleration whatsoever? As well, there may be no practical use other than being a 'neat effect' but if an aircraft were to achieve the sound barrier - (create the 'sonic boom') could finely tuned acceleration/deceleration make a 'chain' of these shock waves?

 

[RainmanTime]

Basically was bored and looking at visuals of aircraft attaining sound barrier speeds and wondered if any theoretical testing had been done in terms of the actual effect - breaking the sound barrier achieves (sonic boom); such as Darby noted.

Your choice of words is always interesting to me. /ttiforum/images/graemlins/smile.gif There has been a great wealth of instrumented testing viz-a-viz the sonic boom effect. The plasma stuff that Darby discussed is way out there. It has been done on a very small scale (in fact, our thermal supersonic tunnel at Cal Poly Pomona was used in the 60s and 70s for some of that early testing), because it takes a lot of energy to sustain a plasma around a moving body unless you are re-entering the atmosphere from space! /ttiforum/images/graemlins/yum.gif

The more interesting work has been done (not surprisingly) by my company, Northop-Grumman:

http://www.dfrc.nasa.gov/Gallery/Photo/F-15B/HTML/EC03-0229-6.html

In fact, the other senior flight controls guy that I work with on my project is the guy who did all the flight controls for that modified F-5 project. The goal was mostly to see how the shaping of the aircraft could lessen the sonic boom effect, for environmental reasons.

One thing I'm curious about and it may sound like a dumb question, but even on a finite level, does the 'sonic boom' affect acceleration whatsoever?

Well, yes... but what it is really affecting is drag. The drag rise on a body as it approaches Mach 1 is extremely large. Hence, for a fixed amount of thrust this drag rise will have an impact on how quickly you can accelerate through the speed of sound(if at all). This is why the most efficient (least fuel burned) method to get beyond Mach 1 is to use gravity. To do this an aircraft gets up to 30,000-40,000 feet and then dives and accelerates beyond Mach 1.

As well, there may be no practical use other than being a 'neat effect' but if an aircraft were to achieve the sound barrier - (create the 'sonic boom') could finely tuned acceleration/deceleration make a 'chain' of these shock waves?

Well, I would not use the words "finely tuned". In theory it might be possible, but it would require very large accels and decels from sub-Mach 1 to well beyond Mach 1.2-1.5. Think of the shock wave (which causes the sonic boom) as a "bubble" (sort of) that begins to form around the aircraft at freestream true airspeeds just under Mach 1. The point of lowest pressure around the vehicle (usually on top of the wing) is where the flow first becomes sonic, and thus where the first signs of the shock wave show up. The further beyond Mach 1 that you fly, the stronger the shock wave around the aircraft becomes. This famous picture is easily past Mach 1.5 because the shock wave is so fully developed around the aircraft:

http://www.defenselink.mil/specials/images/sightofsound.jpg

Once you slow below Mach 1 enough that they disappear, the shock waves just become pressure waves and do not propagate very far. So you see it would take wild swings from below Mach 1 to beyond Mach 1.5 to try and create such an effect. And, of course, it is much easier to exceed Mach 1 the higher up you are in the atmosphere, since the air density goes down. So the higher you are in the atmopshere, the less likely that the shock wave will propagate all the way to the ground.

The Space Shuttle comes in so fast (it is well over Mach 2 until it gets below 20,000 feet) that it forms very strong shock waves which will propagate all the way to the ground, which is why we always hear the double sonic boom here in Los Angeles whenever the shuttle lands at Edwards AFB.

Did this answer some questions? Any more questions result from these answers?
RMT

 

[Angleochoas]

Could it ever be harnessed to be used ultimately as a catalyst?

 

[RainmanTime]

Could it ever be harnessed to be used ultimately as a catalyst?

I'm not really much of a chemist, which is what catalysis is all about. Shock waves are not really chemical reactions. They are strictly a mechanical phenomenon that occurs as a result of all the pressure waves emanating from a body (like the bow waves of a boat) stacking up against each other and forming a discontinuity of air density, pressure, and temperature.

Now, that being said, the temperature difference across a shock wave is great enough that this could be a trigger to a catalysis process... but I am unaware of why one would want to use a process that requires so much energy (to achieve supersonic flow) just to achieve a temperature gradient of that magnitude. Much easier ways to do that. /ttiforum/images/graemlins/smile.gif

RMT

 

[Angleochoas]

Understood. I was more referring to "catalyst" as the secondary definition (nothing to do directly with chemistry) - "something that causes activity between two or more forces without itself being affected.".

Meaning to be used hypethetically to further a reaction or desired result...
With what? Well I was thinking that there may be a variety of potential uses?
Some positive, some perhaps destructive...

When the "bubble" so to say is in the most direct concentrated area around the projectile, could a vaccuum type of environment be used to further condense the vibration? I realize this has alot to do with the positioning of said "bubble" - to the immediate rear/wholly encompassing/dissipated...
Instrumentaion can gauge when the effect is at a close proximity radius the strongest? Or just it all boils down to a complex formula for timing vs. velocity vs. mass? (air current, temperature, etc all variables as well right?).
That's why it would seem instrumentation would be more likely? As the natural environment variable is so undetermined for any potential theorectical test?

There just seems to be something about the production of something so spectacular in terms of technology vs. natural element\vibration...etc
high ordinance weaponary ...on the destructive side (as a variable) all the way to possible atmospheric 'jump gates' ?

Imagine if a fuel mixture could be thought of for the "jump" at said timings...

I'm sure you guys have probably done alot of this testing, and debunked what's plausible a long time ago, is fascinating stuff though ^^.

 

[RainmanTime]

I'm not sure what else I can add here, Angleo. I just don't understand what you are really asking me...

When the "bubble" so to say is in the most direct concentrated area around the projectile, could a vaccuum type of environment be used to further condense the vibration?

What vibration? I do not understand the question.

I realize this has alot to do with the positioning of said "bubble" - to the immediate rear/wholly encompassing/dissipated...
Instrumentaion can gauge when the effect is at a close proximity radius the strongest?

If by "effect" you mean the shock wave... the formation of a shock wave is based on only two factors: Mach number of the flow around the body, and the shape of the body itself. So the only instrumentation you need to determine Mach number are pressure sensors. Typically, an air vehicle is modeled to scale and pressure taps are machined into the model at key points on the body where the aerodynamicists predict the pressures are lowest, or where the largest pressure gradients occur. Throw the model into a wind tunnel, hook the pressure taps up to transducers, fire up the wind tunnel and take the data. This is how we develop a picture of how the flow around the vehicle transitions from subsonic to supersonic.

Or just it all boils down to a complex formula for timing vs. velocity vs. mass? (air current, temperature, etc all variables as well right?).
That's why it would seem instrumentation would be more likely? As the natural environment variable is so undetermined for any potential theorectical test?

Again, I can't quite make out the specifics of what you are asking. But let's start with basics: The good old "ideal gas law" is the starting point for all knowledge of aerodynamics. It tells us how parameters relate to one another at a single point in a fluid mass:

Pressure = Density*Gas Constant*Temperature (P = rho*R*T)

R = a characteristic constant of the fluid itself.
Pressure, Density, and Temperature are the "state variables". So this equation allows us to relate parameters at a givne point in space. We can use Newton's laws of motion to derive dynamic equations that allow us to relate conditions at one point to conditions at another point. The most useful is the pressure-form of the good old energy equation:

P1 + (1/2)*rho*V1^2 + rho*g*h1 = P2 + (1/2)*rho*V2^2 + rho*g*h2

* The "rho*g*h" terms are what are called the hydrostatic terms, and they define the pressure energy in a fluid at any given depth (equivalent to potential energy in the energy equation).
* The P1 and P2 terms are called the static pressure (the pressure independent of velocity) at the respective point in the fluid. This is equivalent to "internal energy" of a body which is neglected in the classical form of the energy equation.
* The "(1/2)*rho*V^2" terms are called dynamic pressure. We can alternately express them in terms of Mach number as:

(1/2)*gamma*P1*Mach1^2 or (1/2)*gamma*P2*Mach2^2

Where "gamma" is a constant associated with the fluid, quite like "R". Dynamic pressure, BTW, is the pressure that is responsible for ALL aerodynamic forces (e.g. lift and drag). Lift and drag varies directly with dynamic pressure.

There just seems to be something about the production of something so spectacular in terms of technology vs. natural element\vibration...etc
high ordinance weaponary ...on the destructive side (as a variable) all the way to possible atmospheric 'jump gates' ?

Imagine if a fuel mixture could be thought of for the "jump" at said timings...

I don't have a clue what you mean by "jump gates". I am hoping that by giving you some of the basic equations used in aerodynamics above that we can have a conversation about things that are well-defined. Because every time you inject a phrase I don't understand (such as "jump gates") I am afraid I have no way to begin to answer your questions.... /ttiforum/images/graemlins/frown.gif

Did any of this help? And if you can explain some of the terms I questioned above better, perhaps we can move along and progress.

RMT

 

[Darby]

the formation of a shock wave is based on only two factors: Mach number of the flow around the body, and the shape of the body itself.

Angelo,

You can see a good example of ths in Ray's F-15 photo. It's easy to see the shock wave at the trailing edge of the aircraft because it's huge. But look just aft of the canope. You see a smaller expansion wave forming at the shoulder of the curved surface. It's both the shape of the surface and the Mach number that has caused it.

 

[Darby]

Angelo,

I understand that you're having some difficulty communicating specific and correct areo terminology to Ray. And Ray is having difficulty "interpreting" the meaning of your terms. If you've read something online that is the basis of your questions it might be helpful if you can direct him to the site(s) so he can see directly what you're asking about. That way he doesn't have to guess at your meaning.

 

[Darby]

Angelo,

Meaning to be used hypethetically to further a reaction or desired result...
With what? Well I was thinking that there may be a variety of potential uses?
Some positive, some perhaps destructive...

When the "bubble" so to say is in the most direct concentrated area around the projectile, could a vaccuum type of environment be used to further condense the vibration? I realize this has alot to do with the positioning of said "bubble" - to the immediate rear/wholly encompassing/dissipated...

Are you asking Ray if the shock wave can be somehow "tuned", maybe by use of variable geometry of the aircraft itself, so the wave can be used as some sort of high energy sonic weapon?

 

[Angleochoas]

Very insightful feedback thx. ^^

I guess to paraphrase for lack of better wording...;
Is there a way known to manipulate the formation of; or alter the shockwave itself?
IE; When the shockwave would hit the critical point of "sonic boom" to a more or less degree...alter/contain the pressure/force?
If the pressure could be "channeled" and used to strengthen an air current for example ...
could that flow be used for a special "boost" fuel mixture...?

Here's one picture I was looking at in reference:
http://en.wikipedia.org/wiki/File:Sonic_boom.svg

If that diagram has any relevance for the formation - then it would appear the pressure is being generated at this juncture (after the initial 'sonic boom'), to the/and off the rear of the projectile - could that not be something utitlized/altered/further compressed?

 

[RainmanTime]

Ahhh, now I am understanding your question(s) better:

I guess to paraphrase for lack of better wording...;
Is there a way known to manipulate the formation of; or alter the shockwave itself?
IE; When the shockwave would hit the critical point of "sonic boom" to a more or less degree...alter/contain the pressure/force?

The only way to manipulate the shock wave is with the geometry of the flying body itself. The most fundamental way to do this is seen in the distinct types of designs of various aerospace vehicles that fly supersonically, and it relates to the bluntness or sharpness of the leading edge that first encounters the shock wave. Supersonic aircraft generally want the shock wave "attached" to the body for various reasons, not the least of which is controllability of the whole airplane improves. To ensure the shock wave is attached, the leading edge of the wings are very pointy, unlike the well-rounded leading edges you see on a conventional subsonic transport jet.

The engine on the SR-71 (the J-58 engine) uses a central spike sticking out its inlet, and this spike can translate forward and backward. The pointy end of the spike ensures the shock wave remains attached, and the position of the spike with respect to the lip of the inlet creates a variable geometry condition (variable inlet capture area, as seen in the photo link above). This, in turn, controls the compression ratio of the air entering the engine's combustor to optimize the mass flow for the fuel flow demanded by the pilot with the throttle.

But on the other side of things, supersonic missiles that use a forward-looking guidance system (either IR or radar), will typically want to prevent the shock wave from becoming attached to the front of the missile. The reason to prevent its attachment has to do with the discontinuities that an attached shock can create for the radar receiver (or especially the IR detectors) that sit behind the radome/nosecone of the missile. These receivers work much better (their outputs are more close to linear) when they "stare" through the rounded, detached bow shock wave. One of the missiles I worked on early in my career (The Rolling Airframe Missile ) uses an IR seeker to home in on cruise missiles heading towards a Navy ship. It has a very well rounded seeker head at the front of the missile to ensure the shock wave does not become attached, and thus present an even view for the IR detector to look through.

If the pressure could be "channeled" and used to strengthen an air current for example ...
could that flow be used for a special "boost" fuel mixture...?

Well, not quite how I think you are meaning to use it, no. But what you are describing is sort of hinting at the very reason for an advanced technology in propulsion called the Supersonic Combustion Ramjet (or Scramjet). You can read all about the scramjet at the link. However, the scramjet is not so much using the shock wave for any purpose as much as it is seeking to keep the airflow completely supersonic through the entire engine to increase engine efficiency and reduce the problems with aerodynamic heating that come from a normal ramjet that decelerates the flow through the shock wave, and this creates great problems with heating at Mach numbers above Mach 3. The scramjet tries to address these problems by maintaining supersonic flow through the inlet and combustion chamber. However, as you can read in the article, this technology is in its infancy and many still question whether we will ever achieve the theoretical benefits it seems to promise.

If that diagram has any relevance for the formation - then it would appear the pressure is being generated at this juncture (after the initial 'sonic boom'), to the/and off the rear of the projectile - could that not be something utitlized/altered/further compressed?

Actually, no, the pressure is not being generated behind the projectile. That is merely the sonic wake trailing behind the vehicle (much as a wake trails behind a boat in the water). The highest pressure gradient exists right at the vehicle itself, where the shock wave forms because of the body disturbing the air as it flows through it. As to whether it could be utilized.... Well, not on the moving vehicle itself because the vehicle is always creating that wave you see in the picture, so it cannot get "behind" it to utilize the sonic pressure wave. Could it be used by the little guy on the ground? Well, yes, but it would not be terribly practical because it is nothing more than a VERY VERY brief pressure pulse that passes by his local area. It is nothing more than a sound wave, and even for very strong shocks, there is not very much useable energy within a single sonic boom sound wave. You would need to create a great many sonic booms, one after another, to be able to collect enough pressure energy to be useful in another application.

I hope this helped answer your questions.
RMT

 

[Angleochoas]

Thanks much, it's very interesting you noted the SR-71 (blackbird);
when I was extremely young I had the chance to view it quite closely at an air show in Toronto. I was quite sad the day it was officially retired - nostalgia and the like...the design was so ahead of it's time.
I found the image of the sonic boom so enthralling, it painted alot of questions and you've answered them as usual very concisely and with insight - thx much /ttiforum/images/graemlins/smile.gif
I would suppose sometimes a great way to digest sciences is to start with something that holds the imagination captivated ^^

 

[Angleochoas]

What kind of air pressure does this sonic boom produce? as well is there any reaction that produces a gas?
If so, can it be chain jumped?
(IE sonic boom = sonic blast)
Idea being for harnessing a creation of power in whatever context.
(It also makes me wonder what we've done in terms of taking air pressure PSI to the limits...)

 

[RainmanTime]

Angleo,

What kind of air pressure does this sonic boom produce?

Another good question, and the answer is: It depends.

What it depends upon is the strength of the shock wave, and that is determined by the Mach number of the flow around the body creating the shock wave. The reason this is a very good question is because this question is answered in total by the National Advisory Committee on Aeronautics (the precursor of NASA) NACA Report #1135. The name of this report is "Equations, Tables, and Charts for Compressible Flow." It is one of the fundamentals of aerodynamics and gas dynamics, and I can guarantee you that all aerospace engineers have a copy of this thin, 69 page booklet in their libraries.

The first 19 pages of this report provides the governing equations for shock waves and expansion waves in supersonic flow, and the remaining pages provide tabulated charts for computing the gas dynamic properties across shock waves and expansion waves. One of the things that is most unusual (and unexpected to those who are uninitiated) is that the computations involved in supersonic flow are actually a great deal simpler than similar computations for subsonic flows.

To answer you question, if you know what the Mach number is for any given flow you can use the tables in NACA 1135 to determine the pressure, temperature, and density changes as you move across the shock wave (from in front of it to behind it). But in general the following is true:

1) TOTAL Pressure drops from in front of the shock (station 1) to behind the shock (station 2). Since total pressure is a measure of the total energy in the flow, what this tells us is that a shock wave is a normal, entropic phenomenon (energy is lost due to the conversion that it represents). However...
2) Static pressure increases from station 1 to station 2, as you cross the shock. For example, for a relatively weak shock (Mach=1.05) the ratio of the static pressure behind the shock to that in front is 1.120. As the Mach number increases this ratio also increases. So for Mach 3.0 the pressure ratio (p2/p1) rises to 10.33!
3) Temperature increases from station 1 to station 2 (i.e. the ratio T2/T1 is greater than one and increases in value as the Mach number increases).
4) Air density increases from station 1 to station 2 (i.e. rho2/rho1>1.0 and increases with Mach number)

as well is there any reaction that produces a gas?

Not in plain old (non-reactive) air, no. But if you accelerated some fairly volatile compound which only needs compression to create a reaction (i.e. ignition) at some body at supersonic speeds, then you could create a reaction. But it is not really practical, at least not in earth's atmosphere.

If so, can it be chain jumped?
(IE sonic boom = sonic blast)

Not in the earth's atmosphere, no. The nitrogen content of our air makes it very stable, and very boring when it comes to trying to sustain a reaction. This is why you need a fuel to make a fuel-air bomb!

Idea being for harnessing a creation of power in whatever context.

The turbofan engine is the best device to do just this, and as you reach Mach numbers greater than 3.0 then the best thing is to get rid of the compressor/fan altogether and simply use a ramjet.

(It also makes me wonder what we've done in terms of taking air pressure PSI to the limits...)

It depends upon what you mean by "limits". The last of NASA's scramjet test vehicles that were flown over the Pacific Test Range a couple years ago would give you an idea of the kinds of pressures we have made an air vehicle experience. That final scramjet test got the test vehicle to a Mach number of around 9.0 at an altitude of 40,000 feet. So let's use my handy NACA-1135 report and our knowledge of the atmosphere to figure out what the static pressure was on the downstream side of the shock wave for that vehicle:

1) On a standard day in the atmosphere at 40,000 feet the atmospheric pressure is about 2.73 PSI (as compared to sea level atmospheric pressure which is 14.69 PSI).
2) Using my NACA-1135 table for a Mach number of 9.0 I find that the pressure ratio p2/p1 for a normal shock wave is 94.33.
3) So the pressure on the vehicle downstream of the shock wave was on the order of 257.4 PSI.

Now for an aerospace vehicle that is a bit high for an external pressure on the skin of a vehicle, but if this were being flown at the same Mach number at sea level the pressure would be about 1385 PSI. But these values pale in comparison to some of the high air pressure closed systems used in some pneumatic applications, which can get as high as 5000 PSI.

RMT